Create an animated torus knot with wireframe overlay in Three.js

Solution:
import * as THREE from 'three';

function createTorusKnot(containerId = 'canvas-container') {
  const container = document.getElementById(containerId);
  if (!container) throw new Error('Container not found');

  const scene = new THREE.Scene();
  scene.background = new THREE.Color('#fab1a0');

  const camera = new THREE.PerspectiveCamera(75, container.clientWidth / container.clientHeight, 0.1, 1000);
  camera.position.z = 5;

  const renderer = new THREE.WebGLRenderer({ antialias: true });
  renderer.setSize(container.clientWidth, container.clientHeight);
  container.appendChild(renderer.domElement);

  const geometry = new THREE.TorusKnotGeometry(1, 0.3, 100, 16);
  const material = new THREE.MeshStandardMaterial({ color: '#74b9ff', roughness: 0.4, metalness: 0.3 });
  const torus = new THREE.Mesh(geometry, material);
  scene.add(torus);

  const wireGeo = new THREE.WireframeGeometry(geometry);
  const wireMat = new THREE.LineBasicMaterial({ color: '#fd79a8' });
  const wireframe = new THREE.LineSegments(wireGeo, wireMat);
  torus.add(wireframe);

  scene.add(new THREE.AmbientLight(0x404040));
  const pointLight = new THREE.PointLight(0xffffff, 1, 100);
  pointLight.position.set(2, 3, 4);
  scene.add(pointLight);

  function animate() {
    requestAnimationFrame(animate);
    torus.rotation.x += 0.015;
    torus.rotation.y += 0.015 * 0.7;
    renderer.render(scene, camera);
  }
  animate();

  return { scene, torus, renderer };
}

// Usage: createTorusKnot();


Raycast from mouse to detect 3D object clicks in Three.js

Solution:
import * as THREE from 'three';

function setupRaycasting(scene, camera, renderer, onIntersect) {
  const raycaster = new THREE.Raycaster();
  const mouse = new THREE.Vector2();

  renderer.domElement.addEventListener('click', (event) => {
    const rect = renderer.domElement.getBoundingClientRect();
    mouse.x = ((event.clientX - rect.left) / rect.width) * 2 - 1;
    mouse.y = -((event.clientY - rect.top) / rect.height) * 2 + 1;

    raycaster.setFromCamera(mouse, camera);
    const intersects = raycaster.intersectObjects(scene.children, true);

    if (intersects.length > 0) {
      const hit = intersects[0];
      console.log('Clicked:', hit.object.name || hit.object.uuid);
      if (typeof onIntersect === 'function') onIntersect(hit);
    }
  });
}

// Usage example:
// const mesh = new THREE.Mesh(geometry, material);
// mesh.name = 'clickable-box';
// scene.add(mesh);
// setupRaycasting(scene, camera, renderer, (hit) => {
//   hit.object.material.color.setHex(Math.random() * 0xffffff);
// });


Build a responsive CSS grid layout with auto-fit columns

Solution:
/* Responsive grid layout */
.grid-container {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(400px, 1fr));
  gap: 1.5rem;
  padding: 2rem;
  max-width: 1200px;
  margin: 0 auto;
}

.grid-item {
  background: #fd79a8;
  border-radius: 12px;
  padding: 1.5rem;
  box-shadow: 0 4px 6px rgba(0,0,0,0.1);
  transition: transform 0.2s ease, box-shadow 0.2s ease;
}

.grid-item:hover {
  transform: translateY(-4px);
  box-shadow: 0 12px 24px rgba(0,0,0,0.15);
}

@media (max-width: 600px) {
  .grid-container {
    grid-template-columns: 1fr;
    padding: 1rem;
  }
}


Create a sticky navigation bar that changes style on scroll

Solution:
/* Sticky nav styles */
.nav-bar {
  position: sticky;
  top: 0;
  z-index: 1000;
  background: transparent;
  padding: 1rem 2rem;
  transition: background 0.3s ease, box-shadow 0.3s ease;
}

.nav-bar.scrolled {
  background: rgba(255, 255, 255, 0.95);
  backdrop-filter: blur(10px);
  box-shadow: 0 2px 10px rgba(0,0,0,0.1);
}

/* JavaScript */
function initStickyNav(navSelector = '.nav-bar') {
  const nav = document.querySelector(navSelector);
  if (!nav) throw new Error('Nav element not found');

  function onScroll() {
    if (window.scrollY > 50) {
      nav.classList.add('scrolled');
    } else {
      nav.classList.remove('scrolled');
    }
  }

  window.addEventListener('scroll', onScroll, { passive: true });
  onScroll(); // Initialize state
  return nav;
}

// Usage: initStickyNav();


Implement debounced search input with fetch API

Solution:
async function debouncedSearch(inputSelector, endpoint, renderFn, delay = 300) {
  const input = document.querySelector(inputSelector);
  if (!input) throw new Error('Input element not found');

  let timeoutId = null;
  let controller = null;

  input.addEventListener('input', (e) => {
    const query = e.target.value.trim();
    clearTimeout(timeoutId);
    if (controller) controller.abort();

    if (!query) {
      renderFn([]);
      return;
    }

    timeoutId = setTimeout(async () => {
      controller = new AbortController();
      try {
        const res = await fetch(`${endpoint}?q=${encodeURIComponent(query)}`, {
          signal: controller.signal
        });
        if (!res.ok) throw new Error(`HTTP ${res.status}`);
        const data = await res.json();
        renderFn(data);
      } catch (err) {
        if (err.name !== 'AbortError') {
          console.error('Search failed:', err);
          renderFn([], err);
        }
      }
    }, delay);
  });
}

// Usage:
// debouncedSearch('#search', '/api/search', (results, err) => {
//   if (err) return showError(err);
//   updateDOM(results);
// });


Create a CSS-only modal with backdrop blur and focus trap

Solution:
/* Modal styles */
.modal-overlay {
  position: fixed;
  inset: 0;
  background: rgba(0, 0, 0, 0.5);
  backdrop-filter: blur(4px);
  display: flex;
  align-items: center;
  justify-content: center;
  opacity: 0;
  visibility: hidden;
  transition: opacity 0.3s ease, visibility 0.3s ease;
}

.modal-overlay.active {
  opacity: 1;
  visibility: visible;
}

.modal-content {
  background: white;
  border-radius: 16px;
  padding: 2rem;
  max-width: 500px;
  width: 90%;
  transform: scale(0.9);
  transition: transform 0.3s ease;
  box-shadow: 0 20px 60px rgba(0,0,0,0.3);
}

.modal-overlay.active .modal-content {
  transform: scale(1);
}

/* JavaScript for focus trap and keyboard */
function initModal(triggerSelector, modalSelector) {
  const trigger = document.querySelector(triggerSelector);
  const modal = document.querySelector(modalSelector);
  if (!trigger || !modal) throw new Error('Modal elements not found');

  const content = modal.querySelector('.modal-content');
  const focusables = content.querySelectorAll('button, [href], input, select, textarea, [tabindex]:not([tabindex="-1"])');

  function open() {
    modal.classList.add('active');
    (focusables[0] || content).focus();
    document.addEventListener('keydown', onKey);
  }

  function close() {
    modal.classList.remove('active');
    document.removeEventListener('keydown', onKey);
    trigger.focus();
  }

  function onKey(e) {
    if (e.key === 'Escape') close();
    if (e.key === 'Tab' && focusables.length > 0) {
      const first = focusables[0];
      const last = focusables[focusables.length - 1];
      if (e.shiftKey && document.activeElement === first) {
        e.preventDefault();
        last.focus();
      } else if (!e.shiftKey && document.activeElement === last) {
        e.preventDefault();
        first.focus();
      }
    }
  }

  trigger.addEventListener('click', open);
  modal.addEventListener('click', (e) => { if (e.target === modal) close(); });

  return { open, close };
}

// Usage: initModal('#open-modal', '#my-modal');


Build a custom dropdown select with keyboard navigation

Solution:
function createCustomSelect(selectElement) {
  if (!(selectElement instanceof HTMLSelectElement)) {
    throw new TypeError('Expected HTMLSelectElement');
  }

  const wrapper = document.createElement('div');
  wrapper.className = 'custom-select';
  wrapper.style.position = 'relative';
  wrapper.style.width = selectElement.offsetWidth + 'px';

  const trigger = document.createElement('button');
  trigger.type = 'button';
  trigger.className = 'select-trigger';
  trigger.textContent = selectElement.options[selectElement.selectedIndex]?.text || 'Select...';
  trigger.setAttribute('aria-haspopup', 'listbox');

  const list = document.createElement('ul');
  list.className = 'select-options';
  list.setAttribute('role', 'listbox');
  list.style.cssText = 'position:absolute;top:100%;left:0;right:0;max-height:200px;overflow:auto;list-style:none;margin:0;padding:0;border:1px solid #ccc;background:#fff;z-index:100;display:none;';

  Array.from(selectElement.options).forEach((opt, i) => {
    const li = document.createElement('li');
    li.textContent = opt.text;
    li.setAttribute('role', 'option');
    li.setAttribute('aria-selected', String(opt.selected));
    li.dataset.value = opt.value;
    li.style.padding = '0.5rem 1rem';
    li.style.cursor = 'pointer';
    li.addEventListener('click', () => {
      selectElement.value = opt.value;
      trigger.textContent = opt.text;
      close();
      selectElement.dispatchEvent(new Event('change'));
    });
    list.appendChild(li);
  });

  wrapper.appendChild(trigger);
  wrapper.appendChild(list);
  selectElement.style.display = 'none';
  selectElement.parentNode.insertBefore(wrapper, selectElement);

  let activeIndex = -1;
  function open() {
    list.style.display = 'block';
    trigger.setAttribute('aria-expanded', 'true');
    activeIndex = Array.from(selectElement.options).findIndex(o => o.selected);
  }
  function close() {
    list.style.display = 'none';
    trigger.setAttribute('aria-expanded', 'false');
  }

  trigger.addEventListener('click', () => {
    list.style.display === 'block' ? close() : open();
  });

  document.addEventListener('click', (e) => {
    if (!wrapper.contains(e.target)) close();
  });

  trigger.addEventListener('keydown', (e) => {
    const items = list.querySelectorAll('li');
    if (e.key === 'ArrowDown') { open(); activeIndex = Math.min(activeIndex + 1, items.length - 1); items[activeIndex]?.focus(); e.preventDefault(); }
    if (e.key === 'ArrowUp') { open(); activeIndex = Math.max(activeIndex - 1, 0); items[activeIndex]?.focus(); e.preventDefault(); }
    if (e.key === 'Enter' || e.key === ' ') { if (list.style.display === 'block' && items[activeIndex]) items[activeIndex].click(); else open(); e.preventDefault(); }
    if (e.key === 'Escape') close();
  });

  return wrapper;
}

// Usage: createCustomSelect(document.getElementById('my-select'));


Implement smooth scroll-to-section with intersection observer highlighting

Solution:
function initScrollSpy(navSelector, sectionSelector, options = {}) {
  const navLinks = document.querySelectorAll(`${navSelector} a[href^="#"]`);
  const sections = document.querySelectorAll(sectionSelector);
  if (!navLinks.length || !sections.length) {
    console.warn('Scroll spy: no nav links or sections found');
    return;
  }

  const offset = options.offset || 80;

  // Smooth scroll on click
  navLinks.forEach(link => {
    link.addEventListener('click', (e) => {
      e.preventDefault();
      const targetId = link.getAttribute('href').slice(1);
      const target = document.getElementById(targetId);
      if (target) {
        window.scrollTo({ top: target.offsetTop - offset, behavior: 'smooth' });
      }
    });
  });

  // Intersection observer for active state
  const observer = new IntersectionObserver((entries) => {
    entries.forEach(entry => {
      if (entry.isIntersecting) {
        navLinks.forEach(l => l.classList.remove('active'));
        const active = document.querySelector(`${navSelector} a[href="#${entry.target.id}"]`);
        if (active) active.classList.add('active');
      }
    });
  }, { rootMargin: `-${offset}px 0px -60% 0px` });

  sections.forEach(section => observer.observe(section));
  return observer;
}

// Usage: initScrollSpy('.side-nav', 'section[data-section]');


Create a draggable range slider with real-time value display

Solution:
function createRangeSlider(container, options = {}) {
  const { min = 0, max = 100, step = 1, value = 50, onChange } = options;
  container = typeof container === 'string' ? document.querySelector(container) : container;
  if (!container) throw new Error('Slider container not found');

  const wrapper = document.createElement('div');
  wrapper.className = 'range-slider';
  wrapper.style.cssText = 'display:flex;align-items:center;gap:1rem;font-family:sans-serif;';

  const input = document.createElement('input');
  input.type = 'range';
  input.min = min;
  input.max = max;
  input.step = step;
  input.value = value;
  input.style.flex = '1';

  const valueDisplay = document.createElement('span');
  valueDisplay.className = 'slider-value';
  valueDisplay.textContent = value;
  valueDisplay.style.minWidth = '3ch';
  valueDisplay.style.textAlign = 'right';
  valueDisplay.style.fontVariantNumeric = 'tabular-nums';

  input.addEventListener('input', (e) => {
    valueDisplay.textContent = e.target.value;
    if (typeof onChange === 'function') onChange(Number(e.target.value));
  });

  wrapper.appendChild(input);
  wrapper.appendChild(valueDisplay);
  container.appendChild(wrapper);

  return { input, valueDisplay, getValue: () => Number(input.value) };
}

// Usage:
// createRangeSlider('#slider-box', {
//   min: 0, max: 255, value: 128,
//   onChange: (v) => { document.body.style.background = `rgb(${v},${v},${v})`; }
// });


Build a color picker canvas with eyedropper and palette export

Solution:
function createColorPicker(canvasId, exportBtnId) {
  const canvas = document.getElementById(canvasId);
  const exportBtn = document.getElementById(exportBtnId);
  if (!canvas || !exportBtn) throw new Error('Color picker elements not found');

  const ctx = canvas.getContext('2d', { willReadFrequently: true });
  let isDragging = false;
  const palette = new Set();

  // Draw a hue-saturation gradient
  function drawGradient() {
    const w = canvas.width;
    const h = canvas.height;
    for (let x = 0; x < w; x++) {
      const hue = (x / w) * 360;
      const grad = ctx.createLinearGradient(0, 0, 0, h);
      grad.addColorStop(0, `hsl(${hue}, 100%, 50%)`);
      grad.addColorStop(1, `hsl(${hue}, 100%, 0%)`);
      ctx.fillStyle = grad;
      ctx.fillRect(x, 0, 1, h);
    }
  }
  drawGradient();

  function pickColor(x, y) {
    const pixel = ctx.getImageData(x, y, 1, 1).data;
    const hex = '#' + [pixel[0], pixel[1], pixel[2]].map(c => c.toString(16).padStart(2, '0')).join('');
    return hex;
  }

  function handleMove(e) {
    const rect = canvas.getBoundingClientRect();
    const x = Math.min(Math.max(e.clientX - rect.left, 0), canvas.width - 1);
    const y = Math.min(Math.max(e.clientY - rect.top, 0), canvas.height - 1);
    const color = pickColor(x, y);
    canvas.style.cursor = 'crosshair';
    if (isDragging) {
      palette.add(color);
      canvas.dispatchEvent(new CustomEvent('colorpicked', { detail: { color, x, y } }));
    }
    return color;
  }

  canvas.addEventListener('mousedown', (e) => { isDragging = true; handleMove(e); });
  canvas.addEventListener('mousemove', handleMove);
  canvas.addEventListener('mouseup', () => { isDragging = false; });
  canvas.addEventListener('mouseleave', () => { isDragging = false; });

  exportBtn.addEventListener('click', () => {
    const colors = Array.from(palette);
    const blob = new Blob([JSON.stringify(colors, null, 2)], { type: 'application/json' });
    const url = URL.createObjectURL(blob);
    const a = document.createElement('a');
    a.href = url;
    a.download = 'palette.json';
    a.click();
    URL.revokeObjectURL(url);
  });

  return { canvas, palette, pickColor };
}

// Usage: createColorPicker('picker-canvas', 'export-btn');


Create a live code preview playground with iframe sandbox

Solution:
function createCodePlayground(containerSelector) {
  const container = document.querySelector(containerSelector);
  if (!container) throw new Error('Playground container not found');

  container.innerHTML = `

        <button data-lang="html">HTML</button>
        <button data-lang="css">CSS</button>
        <button data-lang="js">JS</button>
        <button data-action="run" style="margin-left:auto;">Run</button>

      <textarea class="editor" style="flex:1;resize:none;border:none;padding:1rem;background:#1e1e1e;color:#d4d4d4;font-size:14px;" spellcheck="false"></textarea>

  `;

  const editor = container.querySelector('.editor');
  const preview = container.querySelector('.preview');
  const files = { html: '
Hello World
', css: 'h1 { color: #0984e3; }', js: 'console.log("ready");' };
  let currentLang = 'html';

  editor.value = files.html;

  container.querySelectorAll('button[data-lang]').forEach(btn => {
    btn.addEventListener('click', () => {
      files[currentLang] = editor.value;
      currentLang = btn.dataset.lang;
      editor.value = files[currentLang];
    });
  });

  container.querySelector('button[data-action="run"]').addEventListener('click', () => {
    files[currentLang] = editor.value;
    const doc = `
      <!DOCTYPE html>

      ${files.html}

    `;
    preview.srcdoc = doc;
  });

  return { editor, preview, getFiles: () => ({ ...files }) };
}

// Usage: createCodePlayground('#playground');


Build a resizable split-pane layout with drag handle

Solution:
function createSplitPane(containerSelector, options = {}) {
  const container = document.querySelector(containerSelector);
  if (!container) throw new Error('Split pane container not found');

  const { direction = 'horizontal', initialRatio = 0.5, minSize = 100 } = options;
  const isHorizontal = direction === 'horizontal';

  container.style.display = 'flex';
  container.style.flexDirection = isHorizontal ? 'row' : 'column';
  container.style.height = '100%';
  container.style.overflow = 'hidden';

  const pane1 = document.createElement('div');
  pane1.className = 'pane pane-1';
  pane1.style.flex = `0 0 calc(${initialRatio * 100}% - 4px)`;
  pane1.style.overflow = 'auto';
  pane1.style.minWidth = isHorizontal ? minSize + 'px' : 'auto';
  pane1.style.minHeight = !isHorizontal ? minSize + 'px' : 'auto';

  const handle = document.createElement('div');
  handle.className = 'split-handle';
  handle.style.flex = '0 0 8px';
  handle.style.background = '#e0e0e0';
  handle.style.cursor = isHorizontal ? 'col-resize' : 'row-resize';
  handle.style.userSelect = 'none';

  const pane2 = document.createElement('div');
  pane2.className = 'pane pane-2';
  pane2.style.flex = '1 1 auto';
  pane2.style.overflow = 'auto';
  pane2.style.minWidth = isHorizontal ? minSize + 'px' : 'auto';
  pane2.style.minHeight = !isHorizontal ? minSize + 'px' : 'auto';

  container.appendChild(pane1);
  container.appendChild(handle);
  container.appendChild(pane2);

  let isDragging = false;
  const sizeProp = isHorizontal ? 'clientWidth' : 'clientHeight';

  handle.addEventListener('mousedown', (e) => {
    isDragging = true;
    document.body.style.cursor = isHorizontal ? 'col-resize' : 'row-resize';
  });

  document.addEventListener('mousemove', (e) => {
    if (!isDragging) return;
    const rect = container.getBoundingClientRect();
    const pos = isHorizontal ? e.clientX - rect.left : e.clientY - rect.top;
    const ratio = Math.max(minSize, Math.min(pos, rect[sizeProp] - minSize)) / rect[sizeProp];
    pane1.style.flex = `0 0 calc(${ratio * 100}% - 4px)`;
  });

  document.addEventListener('mouseup', () => {
    isDragging = false;
    document.body.style.cursor = '';
  });

  return { pane1, pane2, handle };
}

// Usage: createSplitPane('#editor-layout', { direction: 'horizontal', initialRatio: 0.4 });


Implement a masonry image grid with lazy loading and lightbox

Solution:
function createMasonryGallery(containerSelector, imageUrls) {
  const container = document.querySelector(containerSelector);
  if (!container) throw new Error('Gallery container not found');

  container.style.columnCount = '3';
  container.style.columnGap = '1rem';

  if (!Array.isArray(imageUrls)) throw new TypeError('imageUrls must be an array');

  // Lightbox overlay
  const lightbox = document.createElement('div');
  lightbox.style.cssText = 'position:fixed;inset:0;background:rgba(0,0,0,0.9);display:none;align-items:center;justify-content:center;z-index:1000;';
  const img = document.createElement('img');
  img.style.maxWidth = '90vw';
  img.style.maxHeight = '90vh';
  img.style.objectFit = 'contain';
  lightbox.appendChild(img);
  lightbox.addEventListener('click', () => { lightbox.style.display = 'none'; });
  document.body.appendChild(lightbox);

  imageUrls.forEach((src, i) => {
    const wrapper = document.createElement('div');
    wrapper.style.breakInside = 'avoid';
    wrapper.style.marginBottom = '1rem';

    const image = document.createElement('img');
    image.dataset.src = src;
    image.alt = `Gallery image ${i + 1}`;
    image.style.width = '100%';
    image.style.borderRadius = '8px';
    image.style.display = 'block';
    image.style.background = '#00b894';
    image.style.minHeight = '150px';

    image.addEventListener('click', () => {
      img.src = src;
      lightbox.style.display = 'flex';
    });

    wrapper.appendChild(image);
    container.appendChild(wrapper);
  });

  // Lazy loading
  const observer = new IntersectionObserver((entries) => {
    entries.forEach(entry => {
      if (entry.isIntersecting && entry.target.dataset.src) {
        entry.target.src = entry.target.dataset.src;
        delete entry.target.dataset.src;
        observer.unobserve(entry.target);
      }
    });
  }, { rootMargin: '200px' });

  container.querySelectorAll('img[data-src]').forEach(img => observer.observe(img));
  return { container, lightbox, observer };
}

// Usage: createMasonryGallery('#gallery', ['/img/1.jpg', '/img/2.jpg']);


Create an image carousel with touch swipe and keyboard controls

Solution:
function createCarousel(containerSelector, slides) {
  const container = document.querySelector(containerSelector);
  if (!container) throw new Error('Carousel container not found');
  if (!Array.isArray(slides) || slides.length === 0) throw new Error('Slides array required');

  let current = 0;

  container.innerHTML = `

      <button class="prev" style="position:absolute;left:1rem;top:50%;transform:translateY(-50%);" aria-label="Previous slide">←</button>
      <button class="next" style="position:absolute;right:1rem;top:50%;transform:translateY(-50%);" aria-label="Next slide">→</button>

  `;

  const track = container.querySelector('.track');
  const indicators = container.querySelector('.indicators');

  slides.forEach((slide, i) => {
    const div = document.createElement('div');
    div.style.minWidth = '100%';
    div.innerHTML = slide;
    track.appendChild(div);

    const dot = document.createElement('button');
    dot.style.width = '10px';
    dot.style.height = '10px';
    dot.style.borderRadius = '50%';
    dot.style.border = 'none';
    dot.style.background = i === 0 ? '#fff' : 'rgba(255,255,255,0.4)';
    dot.addEventListener('click', () => goTo(i));
    indicators.appendChild(dot);
  });

  function goTo(index) {
    current = ((index % slides.length) + slides.length) % slides.length;
    track.style.transform = `translateX(-${current * 100}%)`;
    Array.from(indicators.children).forEach((dot, i) => {
      dot.style.background = i === current ? '#fff' : 'rgba(255,255,255,0.4)';
    });
  }

  container.querySelector('.prev').addEventListener('click', () => goTo(current - 1));
  container.querySelector('.next').addEventListener('click', () => goTo(current + 1));

  // Touch swipe
  let startX = 0;
  container.addEventListener('touchstart', (e) => { startX = e.touches[0].clientX; });
  container.addEventListener('touchend', (e) => {
    const diff = startX - e.changedTouches[0].clientX;
    if (Math.abs(diff) > 50) goTo(current + (diff > 0 ? 1 : -1));
  });

  // Keyboard
  container.setAttribute('tabindex', '0');
  container.addEventListener('keydown', (e) => {
    if (e.key === 'ArrowLeft') goTo(current - 1);
    if (e.key === 'ArrowRight') goTo(current + 1);
  });

  return { goTo, getCurrent: () => current };
}

// Usage: createCarousel('#carousel', ['', '']);


Build an infinite scroll image feed with skeleton placeholders

Solution:
function createInfiniteFeed(containerSelector, fetchPage, options = {}) {
  const container = document.querySelector(containerSelector);
  if (!container) throw new Error('Feed container not found');
  if (typeof fetchPage !== 'function') throw new TypeError('fetchPage must be a function');

  const { pageSize = 20, threshold = 300 } = options;
  let page = 1;
  let isLoading = false;
  let hasMore = true;

  function createSkeletons(count) {
    const frag = document.createDocumentFragment();
    for (let i = 0; i < count; i++) {
      const div = document.createElement('div');
      div.className = 'skeleton';
      div.style.cssText = 'height:200px;background:linear-gradient(90deg,#f0f0f0 25%,#e0e0e0 50%,#f0f0f0 75%);background-size:200% 100%;animation:shimmer 1.5s infinite;border-radius:8px;';
      frag.appendChild(div);
    }
    return frag;
  }

  // Add shimmer keyframes if not present
  if (!document.getElementById('skeleton-styles')) {
    const style = document.createElement('style');
    style.id = 'skeleton-styles';
    style.textContent = '@keyframes shimmer { 0% { background-position: 200% 0; } 100% { background-position: -200% 0; } }';
    document.head.appendChild(style);
  }

  async function loadMore() {
    if (isLoading || !hasMore) return;
    isLoading = true;
    const skeletons = createSkeletons(pageSize);
    container.appendChild(skeletons);

    try {
      const items = await fetchPage(page, pageSize);
      skeletons.remove();
      if (!items || items.length === 0) {
        hasMore = false;
        return;
      }
      items.forEach(item => container.appendChild(item));
      page++;
    } catch (err) {
      console.error('Feed load error:', err);
      skeletons.remove();
    } finally {
      isLoading = false;
    }
  }

  const sentinel = document.createElement('div');
  sentinel.style.height = '1px';
  container.appendChild(sentinel);

  const observer = new IntersectionObserver((entries) => {
    if (entries[0].isIntersecting) loadMore();
  }, { rootMargin: `${threshold}px` });
  observer.observe(sentinel);

  loadMore();
  return { loadMore, observer };
}

// Usage:
// createInfiniteFeed('#feed', async (page, size) => {
//   const res = await fetch(`/api/images?page=${page}&size=$250px`);
//   const data = await res.json();
//   return data.map(url => { const img = document.createElement('img'); img.src = url; return img; });
// });


Create a 2D canvas game loop with delta-time physics

Solution:
class GameEngine {
  constructor(canvasId, options = {}) {
    this.canvas = document.getElementById(canvasId);
    if (!this.canvas) throw new Error('Canvas not found: ' + canvasId);
    this.ctx = this.canvas.getContext('2d');
    this.entities = [];
    this.lastTime = 0;
    this.running = false;
    this.fps = 60;

    this.canvas.width = options.width || 800;
    this.canvas.height = options.height || 600;
    this.canvas.style.background = options.bg || '#e17055';
  }

  addEntity(entity) {
    if (!entity.update || !entity.draw) {
      throw new TypeError('Entity must have update(dt) and draw(ctx) methods');
    }
    this.entities.push(entity);
    return this;
  }

  start() {
    this.running = true;
    requestAnimationFrame((t) => this.loop(t));
  }

  stop() {
    this.running = false;
  }

  loop(timestamp) {
    if (!this.running) return;
    const dt = Math.min((timestamp - this.lastTime) / 1000, 0.05); // Cap delta
    this.lastTime = timestamp;

    this.ctx.clearRect(0, 0, this.canvas.width, this.canvas.height);

    for (const entity of this.entities) {
      entity.update(dt, this.canvas.width, this.canvas.height);
      entity.draw(this.ctx);
    }

    requestAnimationFrame((t) => this.loop(t));
  }
}

// Usage:
// const engine = new GameEngine('game-canvas', { width: 800, height: 600 });
// engine.addEntity({ update(dt, w, h) { this.x += 100 * dt; }, draw(ctx) { ctx.fillRect(this.x, 100, 20, 20); }, x: 0 });
// engine.start();


Implement AABB collision detection for rectangular game entities

Solution:
function checkAABBCollision(a, b) {
  if (!a || !b) throw new Error('Both entities required for collision check');
  return (
    a.x < b.x + b.width &&
    a.x + a.width > b.x &&
    a.y < b.y + b.height &&
    a.y + a.height > b.y
  );
}

function resolveAABBOverlap(a, b) {
  const overlapX = Math.min(a.x + a.width, b.x + b.width) - Math.max(a.x, b.x);
  const overlapY = Math.min(a.y + a.height, b.y + b.height) - Math.max(a.y, b.y);

  if (overlapX < overlapY) {
    const dir = a.x < b.x ? -1 : 1;
    a.x += (overlapX / 2) * dir;
    b.x -= (overlapX / 2) * dir;
  } else {
    const dir = a.y < b.y ? -1 : 1;
    a.y += (overlapY / 2) * dir;
    b.y -= (overlapY / 2) * dir;
  }
}

class PhysicsWorld {
  constructor() {
    this.bodies = [];
  }

  add(body) {
    if (typeof body.x !== 'number' || typeof body.y !== 'number') {
      throw new TypeError('Body must have numeric x and y properties');
    }
    this.bodies.push(body);
  }

  step() {
    for (let i = 0; i < this.bodies.length; i++) {
      for (let j = i + 1; j < this.bodies.length; j++) {
        if (checkAABBCollision(this.bodies[i], this.bodies[j])) {
          resolveAABBOverlap(this.bodies[i], this.bodies[j]);
          if (this.bodies[i].onCollision) this.bodies[i].onCollision(this.bodies[j]);
          if (this.bodies[j].onCollision) this.bodies[j].onCollision(this.bodies[i]);
        }
      }
    }
  }
}

// Usage:
// const world = new PhysicsWorld();
// world.add({ x: 0, y: 0, width: 32, height: 32, onCollision(other) { console.log('hit!'); } });
// world.step();


Build a sprite animation system with frame clipping and playback controls

Solution:
class SpriteAnimator {
  constructor(image, frameWidth, frameHeight, frameCount) {
    if (!(image instanceof HTMLImageElement)) throw new TypeError('Expected HTMLImageElement');
    this.image = image;
    this.frameWidth = frameWidth;
    this.frameHeight = frameHeight;
    this.frameCount = frameCount;
    this.currentFrame = 0;
    this.elapsed = 0;
    this.fps = 10;
    this.playing = true;
    this.loop = true;
  }

  update(dt) {
    if (!this.playing) return;
    this.elapsed += dt;
    const frameDuration = 1 / this.fps;
    if (this.elapsed >= frameDuration) {
      this.elapsed -= frameDuration;
      this.currentFrame++;
      if (this.currentFrame >= this.frameCount) {
        if (this.loop) this.currentFrame = 0;
        else { this.currentFrame = this.frameCount - 1; this.playing = false; }
      }
    }
  }

  draw(ctx, x, y, options = {}) {
    const sx = (this.currentFrame * this.frameWidth) % this.image.width;
    const sy = Math.floor((this.currentFrame * this.frameWidth) / this.image.width) * this.frameHeight;
    const scale = options.scale || 1;
    ctx.drawImage(
      this.image,
      sx, sy, this.frameWidth, this.frameHeight,
      x, y, this.frameWidth * scale, this.frameHeight * scale
    );
  }

  play() { this.playing = true; }
  pause() { this.playing = false; }
  reset() { this.currentFrame = 0; this.elapsed = 0; }
  setFrame(index) { this.currentFrame = Math.max(0, Math.min(index, this.frameCount - 1)); }
}

// Usage:
// const img = new Image();
// img.src = '/sprites/player.png';
// img.onload = () => {
//   const anim = new SpriteAnimator(img, 32, 32, 8);
//   // In game loop: anim.update(dt); anim.draw(ctx, 100, 100);
// };


Implement a tilemap renderer with camera scrolling and culling

Solution:
class TilemapRenderer {
  constructor(canvasId, tileSize = 32) {
    this.canvas = document.getElementById(canvasId);
    if (!this.canvas) throw new Error('Canvas not found');
    this.ctx = this.canvas.getContext('2d');
    this.tileSize = tileSize;
    this.camera = { x: 0, y: 0 };
    this.tiles = []; // 2D array of tile IDs
    this.tileset = new Map(); // ID -> color or image
  }

  loadMap(tiles) {
    if (!Array.isArray(tiles) || !tiles.every(row => Array.isArray(row))) {
      throw new TypeError('tiles must be a 2D array');
    }
    this.tiles = tiles;
  }

  registerTile(id, renderable) {
    this.tileset.set(id, renderable);
  }

  setCamera(x, y) {
    this.camera.x = x;
    this.camera.y = y;
  }

  render() {
    const cols = Math.ceil(this.canvas.width / this.tileSize) + 1;
    const rows = Math.ceil(this.canvas.height / this.tileSize) + 1;
    const startCol = Math.floor(this.camera.x / this.tileSize);
    const startRow = Math.floor(this.camera.y / this.tileSize);

    for (let r = 0; r < rows; r++) {
      for (let c = 0; c < cols; c++) {
        const tileRow = startRow + r;
        const tileCol = startCol + c;
        if (tileRow < 0 || tileRow >= this.tiles.length) continue;
        if (tileCol < 0 || tileCol >= this.tiles[tileRow].length) continue;

        const tileId = this.tiles[tileRow][tileCol];
        const screenX = c * this.tileSize - (this.camera.x % this.tileSize);
        const screenY = r * this.tileSize - (this.camera.y % this.tileSize);

        const renderable = this.tileset.get(tileId);
        if (typeof renderable === 'string') {
          this.ctx.fillStyle = renderable;
          this.ctx.fillRect(screenX, screenY, this.tileSize, this.tileSize);
        } else if (renderable instanceof HTMLImageElement) {
          this.ctx.drawImage(renderable, screenX, screenY, this.tileSize, this.tileSize);
        }
      }
    }
  }
}

// Usage:
// const renderer = new TilemapRenderer('game-canvas', 32);
// renderer.loadMap([[0,0,1],[0,1,1],[1,1,1]]);
// renderer.registerTile(0, '#fdcb6e');
// renderer.registerTile(1, '#e17055');
// renderer.setCamera(100, 50);
// renderer.render();


Create a particle explosion effect on canvas for game feedback

Solution:
class ParticleSystem {
  constructor() {
    this.particles = [];
  }

  emit(x, y, options = {}) {
    const {
      count = 20,
      speed = 0.01,
      life = 1.0,
      colors = ['#6c5ce7', '#0984e3', '#e17055'],
      size = 4,
      gravity = 200
    } = options;

    for (let i = 0; i < count; i++) {
      const angle = (Math.PI * 2 * i) / count + (Math.random() - 0.5) * 0.5;
      const velocity = speed * (0.5 + Math.random() * 0.5);
      this.particles.push({
        x, y,
        vx: Math.cos(angle) * velocity,
        vy: Math.sin(angle) * velocity,
        life,
        maxLife: life,
        color: colors[Math.floor(Math.random() * colors.length)],
        size: size * (0.5 + Math.random()),
        gravity
      });
    }
  }

  update(dt) {
    for (let i = this.particles.length - 1; i >= 0; i--) {
      const p = this.particles[i];
      p.x += p.vx * dt;
      p.y += p.vy * dt;
      p.vy += p.gravity * dt;
      p.life -= dt;
      if (p.life <= 0) this.particles.splice(i, 1);
    }
  }

  draw(ctx) {
    for (const p of this.particles) {
      const alpha = Math.max(0, p.life / p.maxLife);
      ctx.globalAlpha = alpha;
      ctx.fillStyle = p.color;
      ctx.beginPath();
      ctx.arc(p.x, p.y, p.size * alpha, 0, Math.PI * 2);
      ctx.fill();
    }
    ctx.globalAlpha = 1;
  }
}

// Usage:
// const particles = new ParticleSystem();
// particles.emit(400, 300, { count: 30, speed: 150, colors: ['#dfe6e9', '#a29bfe', '#dfe6e9'] });
// // In game loop: particles.update(dt); particles.draw(ctx);


Create a Three.js scene with a rotating colored cube

Solution:
import * as THREE from 'three';

function createCubeScene(containerId = 'canvas-container') {
  const container = document.getElementById(containerId);
  if (!container) throw new Error('Container not found: ' + containerId);

  const scene = new THREE.Scene();
  scene.background = new THREE.Color('#4ecdc4');

  const camera = new THREE.PerspectiveCamera(75, container.clientWidth / container.clientHeight, 0.1, 1000);
  camera.position.z = 5;

  const renderer = new THREE.WebGLRenderer({ antialias: true });
  renderer.setSize(container.clientWidth, container.clientHeight);
  renderer.setPixelRatio(window.devicePixelRatio);
  container.appendChild(renderer.domElement);

  const geometry = new THREE.BoxGeometry(1, 1, 1);
  const material = new THREE.MeshStandardMaterial({ color: '#a29bfe', roughness: 0.3, metalness: 0.1 });
  const cube = new THREE.Mesh(geometry, material);
  scene.add(cube);

  const light = new THREE.DirectionalLight(0xffffff, 1);
  light.position.set(5, 5, 5);
  scene.add(light);
  scene.add(new THREE.AmbientLight(0x404040));

  function animate() {
    requestAnimationFrame(animate);
    cube.rotation.x += 0.01;
    cube.rotation.y += 0.01;
    renderer.render(scene, camera);
  }
  animate();

  window.addEventListener('resize', () => {
    camera.aspect = container.clientWidth / container.clientHeight;
    camera.updateProjectionMatrix();
    renderer.setSize(container.clientWidth, container.clientHeight);
  });

  return { scene, camera, renderer, cube };
}

// Usage: createCubeScene();


Load a GLTF 3D model in Three.js with orbit controls

Solution:
import * as THREE from 'three';
import { GLTFLoader } from 'three/examples/jsm/loaders/GLTFLoader.js';
import { OrbitControls } from 'three/examples/jsm/controls/OrbitControls.js';

async function loadModel(url, containerId = 'canvas-container') {
  const container = document.getElementById(containerId);
  if (!container) throw new Error('Container not found');

  const scene = new THREE.Scene();
  scene.background = new THREE.Color('#96ceb4');
  scene.fog = new THREE.Fog('#96ceb4', 10, 50);

  const camera = new THREE.PerspectiveCamera(45, container.clientWidth / container.clientHeight, 0.1, 100);
  camera.position.set(0, 2, 5);

  const renderer = new THREE.WebGLRenderer({ antialias: true });
  renderer.setSize(container.clientWidth, container.clientHeight);
  renderer.shadowMap.enabled = true;
  container.appendChild(renderer.domElement);

  const controls = new OrbitControls(camera, renderer.domElement);
  controls.enableDamping = true;
  controls.dampingFactor = 0.05;

  scene.add(new THREE.AmbientLight(0xffffff, 0.5));
  const dirLight = new THREE.DirectionalLight(0xffffff, 1);
  dirLight.position.set(5, 10, 7);
  dirLight.castShadow = true;
  scene.add(dirLight);

  const loader = new GLTFLoader();
  try {
    const gltf = await loader.loadAsync(url);
    const model = gltf.scene;
    model.traverse(child => { if (child.isMesh) child.castShadow = true; });
    scene.add(model);
  } catch (err) {
    console.error('Failed to load model:', err);
    throw err;
  }

  function animate() {
    requestAnimationFrame(animate);
    controls.update();
    renderer.render(scene, camera);
  }
  animate();

  return { scene, camera, controls };
}

// Usage: loadModel('/models/character.glb');


Create a particle system in Three.js with random motion

Solution:
import * as THREE from 'three';

function createParticles(count = 20, containerId = 'canvas-container') {
  const container = document.getElementById(containerId);
  if (!container) throw new Error('Container not found');

  const scene = new THREE.Scene();
  const camera = new THREE.PerspectiveCamera(75, container.clientWidth / container.clientHeight, 0.1, 1000);
  camera.position.z = 30;

  const renderer = new THREE.WebGLRenderer({ antialias: true, alpha: true });
  renderer.setSize(container.clientWidth, container.clientHeight);
  container.appendChild(renderer.domElement);

  const geometry = new THREE.BufferGeometry();
  const positions = new Float32Array(count * 3);
  const velocities = [];

  for (let i = 0; i < count; i++) {
    positions[i * 3] = (Math.random() - 0.5) * 50;
    positions[i * 3 + 1] = (Math.random() - 0.5) * 50;
    positions[i * 3 + 2] = (Math.random() - 0.5) * 50;
    velocities.push({
      x: (Math.random() - 0.5) * 0.03,
      y: (Math.random() - 0.5) * 0.03,
      z: (Math.random() - 0.5) * 0.03
    });
  }

  geometry.setAttribute('position', new THREE.BufferAttribute(positions, 3));
  const material = new THREE.PointsMaterial({ color: '#e17055', size: 0.5, transparent: true, opacity: 0.8 });
  const particles = new THREE.Points(geometry, material);
  scene.add(particles);

  function animate() {
    requestAnimationFrame(animate);
    const pos = geometry.attributes.position.array;
    for (let i = 0; i < count; i++) {
      pos[i * 3] += velocities[i].x;
      pos[i * 3 + 1] += velocities[i].y;
      pos[i * 3 + 2] += velocities[i].z;
      if (Math.abs(pos[i * 3]) > 25) velocities[i].x *= -1;
      if (Math.abs(pos[i * 3 + 1]) > 25) velocities[i].y *= -1;
      if (Math.abs(pos[i * 3 + 2]) > 25) velocities[i].z *= -1;
    }
    geometry.attributes.position.needsUpdate = true;
    renderer.render(scene, camera);
  }
  animate();

  return { scene, particles, renderer };
}

// Usage: createParticles(200);


Create a reflective sphere with environment mapping in Three.js

Solution:
import * as THREE from 'three';

function createReflectiveSphere(containerId = 'canvas-container') {
  const container = document.getElementById(containerId);
  if (!container) throw new Error('Container not found');

  const scene = new THREE.Scene();
  const camera = new THREE.PerspectiveCamera(75, container.clientWidth / container.clientHeight, 0.1, 1000);
  camera.position.z = 3;

  const renderer = new THREE.WebGLRenderer({ antialias: true });
  renderer.setSize(container.clientWidth, container.clientHeight);
  renderer.toneMapping = THREE.ACESFilmicToneMapping;
  container.appendChild(renderer.domElement);

  const pmremGenerator = new THREE.PMREMGenerator(renderer);
  const envScene = new THREE.Scene();
  envScene.background = new THREE.Color('#6c5ce7');
  envScene.add(new THREE.Mesh(
    new THREE.SphereGeometry(10, 32, 32),
    new THREE.MeshBasicMaterial({ color: '#45b7d1', side: THREE.BackSide })
  ));
  const envMap = pmremGenerator.fromScene(envScene).texture;

  const geometry = new THREE.SphereGeometry(1, 64, 64);
  const material = new THREE.MeshPhysicalMaterial({
    color: '#4ecdc4',
    metalness: 1.0,
    roughness: 0.1,
    envMap,
    envMapIntensity: 1.0
  });
  const sphere = new THREE.Mesh(geometry, material);
  scene.add(sphere);

  function animate() {
    requestAnimationFrame(animate);
    sphere.rotation.y += 0.005;
    renderer.render(scene, camera);
  }
  animate();

  return { scene, sphere, renderer };
}

// Usage: createReflectiveSphere();


Build a Three.js first-person camera controller with WASD movement

Solution:
import * as THREE from 'three';

function createFPSController(containerId = 'canvas-container') {
  const container = document.getElementById(containerId);
  if (!container) throw new Error('Container not found');

  const scene = new THREE.Scene();
  scene.background = new THREE.Color('#ff6b6b');

  const camera = new THREE.PerspectiveCamera(75, container.clientWidth / container.clientHeight, 0.1, 1000);
  camera.position.y = 1.7;

  const renderer = new THREE.WebGLRenderer({ antialias: true });
  renderer.setSize(container.clientWidth, container.clientHeight);
  container.appendChild(renderer.domElement);

  // Floor
  const floor = new THREE.Mesh(
    new THREE.PlaneGeometry(50, 50),
    new THREE.MeshStandardMaterial({ color: '#00b894' })
  );
  floor.rotation.x = -Math.PI / 2;
  floor.receiveShadow = true;
  scene.add(floor);

  scene.add(new THREE.AmbientLight(0x404040));
  const dirLight = new THREE.DirectionalLight(0xffffff, 0.8);
  dirLight.position.set(5, 10, 5);
  scene.add(dirLight);

  const keys = { w: false, a: false, s: false, d: false };
  const velocity = new THREE.Vector3();
  const direction = new THREE.Vector3();

  document.addEventListener('keydown', (e) => { if (keys.hasOwnProperty(e.key.toLowerCase())) keys[e.key.toLowerCase()] = true; });
  document.addEventListener('keyup', (e) => { if (keys.hasOwnProperty(e.key.toLowerCase())) keys[e.key.toLowerCase()] = false; });

  container.addEventListener('click', () => container.requestPointerLock());
  document.addEventListener('mousemove', (e) => {
    if (document.pointerLockElement === container) {
      camera.rotation.y -= e.movementX * 0.002;
      camera.rotation.x -= e.movementY * 0.002;
      camera.rotation.x = Math.max(-Math.PI / 2, Math.min(Math.PI / 2, camera.rotation.x));
    }
  });

  const clock = new THREE.Clock();
  function animate() {
    requestAnimationFrame(animate);
    const delta = clock.getDelta();
    velocity.x -= velocity.x * 10 * delta;
    velocity.z -= velocity.z * 10 * delta;
    direction.z = Number(keys.w) - Number(keys.s);
    direction.x = Number(keys.a) - Number(keys.d);
    direction.normalize();
    if (keys.w || keys.s) velocity.z -= direction.z * 40 * delta;
    if (keys.a || keys.d) velocity.x -= direction.x * 40 * delta;
    camera.translateX(-velocity.x * delta);
    camera.translateZ(-velocity.z * delta);
    camera.position.y = 1.7;
    renderer.render(scene, camera);
  }
  animate();

  return { scene, camera, renderer };
}

// Usage: createFPSController();


Create an animated torus knot with wireframe overlay in Three.js

Solution:
import * as THREE from 'three';

function createTorusKnot(containerId = 'canvas-container') {
  const container = document.getElementById(containerId);
  if (!container) throw new Error('Container not found');

  const scene = new THREE.Scene();
  scene.background = new THREE.Color('#0984e3');

  const camera = new THREE.PerspectiveCamera(75, container.clientWidth / container.clientHeight, 0.1, 1000);
  camera.position.z = 5;

  const renderer = new THREE.WebGLRenderer({ antialias: true });
  renderer.setSize(container.clientWidth, container.clientHeight);
  container.appendChild(renderer.domElement);

  const geometry = new THREE.TorusKnotGeometry(1, 0.3, 100, 16);
  const material = new THREE.MeshStandardMaterial({ color: '#45b7d1', roughness: 0.4, metalness: 0.3 });
  const torus = new THREE.Mesh(geometry, material);
  scene.add(torus);

  const wireGeo = new THREE.WireframeGeometry(geometry);
  const wireMat = new THREE.LineBasicMaterial({ color: '#0984e3' });
  const wireframe = new THREE.LineSegments(wireGeo, wireMat);
  torus.add(wireframe);

  scene.add(new THREE.AmbientLight(0x404040));
  const pointLight = new THREE.PointLight(0xffffff, 1, 100);
  pointLight.position.set(2, 3, 4);
  scene.add(pointLight);

  function animate() {
    requestAnimationFrame(animate);
    torus.rotation.x += 0.05;
    torus.rotation.y += 0.05 * 0.7;
    renderer.render(scene, camera);
  }
  animate();

  return { scene, torus, renderer };
}

// Usage: createTorusKnot();


Raycast from mouse to detect 3D object clicks in Three.js

Solution:
import * as THREE from 'three';

function setupRaycasting(scene, camera, renderer, onIntersect) {
  const raycaster = new THREE.Raycaster();
  const mouse = new THREE.Vector2();

  renderer.domElement.addEventListener('click', (event) => {
    const rect = renderer.domElement.getBoundingClientRect();
    mouse.x = ((event.clientX - rect.left) / rect.width) * 2 - 1;
    mouse.y = -((event.clientY - rect.top) / rect.height) * 2 + 1;

    raycaster.setFromCamera(mouse, camera);
    const intersects = raycaster.intersectObjects(scene.children, true);

    if (intersects.length > 0) {
      const hit = intersects[0];
      console.log('Clicked:', hit.object.name || hit.object.uuid);
      if (typeof onIntersect === 'function') onIntersect(hit);
    }
  });
}

// Usage example:
// const mesh = new THREE.Mesh(geometry, material);
// mesh.name = 'clickable-box';
// scene.add(mesh);
// setupRaycasting(scene, camera, renderer, (hit) => {
//   hit.object.material.color.setHex(Math.random() * 0xffffff);
// });


Build a responsive CSS grid layout with auto-fit columns

Solution:
/* Responsive grid layout */
.grid-container {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(400px, 1fr));
  gap: 1.5rem;
  padding: 2rem;
  max-width: 1200px;
  margin: 0 auto;
}

.grid-item {
  background: #fab1a0;
  border-radius: 12px;
  padding: 1.5rem;
  box-shadow: 0 4px 6px rgba(0,0,0,0.1);
  transition: transform 0.2s ease, box-shadow 0.2s ease;
}

.grid-item:hover {
  transform: translateY(-4px);
  box-shadow: 0 12px 24px rgba(0,0,0,0.15);
}

@media (max-width: 600px) {
  .grid-container {
    grid-template-columns: 1fr;
    padding: 1rem;
  }
}


Create a sticky navigation bar that changes style on scroll

Solution:
/* Sticky nav styles */
.nav-bar {
  position: sticky;
  top: 0;
  z-index: 1000;
  background: transparent;
  padding: 1rem 2rem;
  transition: background 0.3s ease, box-shadow 0.3s ease;
}

.nav-bar.scrolled {
  background: rgba(255, 255, 255, 0.95);
  backdrop-filter: blur(10px);
  box-shadow: 0 2px 10px rgba(0,0,0,0.1);
}

/* JavaScript */
function initStickyNav(navSelector = '.nav-bar') {
  const nav = document.querySelector(navSelector);
  if (!nav) throw new Error('Nav element not found');

  function onScroll() {
    if (window.scrollY > 50) {
      nav.classList.add('scrolled');
    } else {
      nav.classList.remove('scrolled');
    }
  }

  window.addEventListener('scroll', onScroll, { passive: true });
  onScroll(); // Initialize state
  return nav;
}

// Usage: initStickyNav();


Implement debounced search input with fetch API

Solution:
async function debouncedSearch(inputSelector, endpoint, renderFn, delay = 300) {
  const input = document.querySelector(inputSelector);
  if (!input) throw new Error('Input element not found');

  let timeoutId = null;
  let controller = null;

  input.addEventListener('input', (e) => {
    const query = e.target.value.trim();
    clearTimeout(timeoutId);
    if (controller) controller.abort();

    if (!query) {
      renderFn([]);
      return;
    }

    timeoutId = setTimeout(async () => {
      controller = new AbortController();
      try {
        const res = await fetch(`${endpoint}?q=${encodeURIComponent(query)}`, {
          signal: controller.signal
        });
        if (!res.ok) throw new Error(`HTTP ${res.status}`);
        const data = await res.json();
        renderFn(data);
      } catch (err) {
        if (err.name !== 'AbortError') {
          console.error('Search failed:', err);
          renderFn([], err);
        }
      }
    }, delay);
  });
}

// Usage:
// debouncedSearch('#search', '/api/search', (results, err) => {
//   if (err) return showError(err);
//   updateDOM(results);
// });


Create a CSS-only modal with backdrop blur and focus trap

Solution:
/* Modal styles */
.modal-overlay {
  position: fixed;
  inset: 0;
  background: rgba(0, 0, 0, 0.5);
  backdrop-filter: blur(4px);
  display: flex;
  align-items: center;
  justify-content: center;
  opacity: 0;
  visibility: hidden;
  transition: opacity 0.3s ease, visibility 0.3s ease;
}

.modal-overlay.active {
  opacity: 1;
  visibility: visible;
}

.modal-content {
  background: white;
  border-radius: 16px;
  padding: 2rem;
  max-width: 500px;
  width: 90%;
  transform: scale(0.9);
  transition: transform 0.3s ease;
  box-shadow: 0 20px 60px rgba(0,0,0,0.3);
}

.modal-overlay.active .modal-content {
  transform: scale(1);
}

/* JavaScript for focus trap and keyboard */
function initModal(triggerSelector, modalSelector) {
  const trigger = document.querySelector(triggerSelector);
  const modal = document.querySelector(modalSelector);
  if (!trigger || !modal) throw new Error('Modal elements not found');

  const content = modal.querySelector('.modal-content');
  const focusables = content.querySelectorAll('button, [href], input, select, textarea, [tabindex]:not([tabindex="-1"])');

  function open() {
    modal.classList.add('active');
    (focusables[0] || content).focus();
    document.addEventListener('keydown', onKey);
  }

  function close() {
    modal.classList.remove('active');
    document.removeEventListener('keydown', onKey);
    trigger.focus();
  }

  function onKey(e) {
    if (e.key === 'Escape') close();
    if (e.key === 'Tab' && focusables.length > 0) {
      const first = focusables[0];
      const last = focusables[focusables.length - 1];
      if (e.shiftKey && document.activeElement === first) {
        e.preventDefault();
        last.focus();
      } else if (!e.shiftKey && document.activeElement === last) {
        e.preventDefault();
        first.focus();
      }
    }
  }

  trigger.addEventListener('click', open);
  modal.addEventListener('click', (e) => { if (e.target === modal) close(); });

  return { open, close };
}

// Usage: initModal('#open-modal', '#my-modal');


Build a custom dropdown select with keyboard navigation

Solution:
function createCustomSelect(selectElement) {
  if (!(selectElement instanceof HTMLSelectElement)) {
    throw new TypeError('Expected HTMLSelectElement');
  }

  const wrapper = document.createElement('div');
  wrapper.className = 'custom-select';
  wrapper.style.position = 'relative';
  wrapper.style.width = selectElement.offsetWidth + 'px';

  const trigger = document.createElement('button');
  trigger.type = 'button';
  trigger.className = 'select-trigger';
  trigger.textContent = selectElement.options[selectElement.selectedIndex]?.text || 'Select...';
  trigger.setAttribute('aria-haspopup', 'listbox');

  const list = document.createElement('ul');
  list.className = 'select-options';
  list.setAttribute('role', 'listbox');
  list.style.cssText = 'position:absolute;top:100%;left:0;right:0;max-height:200px;overflow:auto;list-style:none;margin:0;padding:0;border:1px solid #ccc;background:#fff;z-index:100;display:none;';

  Array.from(selectElement.options).forEach((opt, i) => {
    const li = document.createElement('li');
    li.textContent = opt.text;
    li.setAttribute('role', 'option');
    li.setAttribute('aria-selected', String(opt.selected));
    li.dataset.value = opt.value;
    li.style.padding = '0.5rem 1rem';
    li.style.cursor = 'pointer';
    li.addEventListener('click', () => {
      selectElement.value = opt.value;
      trigger.textContent = opt.text;
      close();
      selectElement.dispatchEvent(new Event('change'));
    });
    list.appendChild(li);
  });

  wrapper.appendChild(trigger);
  wrapper.appendChild(list);
  selectElement.style.display = 'none';
  selectElement.parentNode.insertBefore(wrapper, selectElement);

  let activeIndex = -1;
  function open() {
    list.style.display = 'block';
    trigger.setAttribute('aria-expanded', 'true');
    activeIndex = Array.from(selectElement.options).findIndex(o => o.selected);
  }
  function close() {
    list.style.display = 'none';
    trigger.setAttribute('aria-expanded', 'false');
  }

  trigger.addEventListener('click', () => {
    list.style.display === 'block' ? close() : open();
  });

  document.addEventListener('click', (e) => {
    if (!wrapper.contains(e.target)) close();
  });

  trigger.addEventListener('keydown', (e) => {
    const items = list.querySelectorAll('li');
    if (e.key === 'ArrowDown') { open(); activeIndex = Math.min(activeIndex + 1, items.length - 1); items[activeIndex]?.focus(); e.preventDefault(); }
    if (e.key === 'ArrowUp') { open(); activeIndex = Math.max(activeIndex - 1, 0); items[activeIndex]?.focus(); e.preventDefault(); }
    if (e.key === 'Enter' || e.key === ' ') { if (list.style.display === 'block' && items[activeIndex]) items[activeIndex].click(); else open(); e.preventDefault(); }
    if (e.key === 'Escape') close();
  });

  return wrapper;
}

// Usage: createCustomSelect(document.getElementById('my-select'));


Implement smooth scroll-to-section with intersection observer highlighting

Solution:
function initScrollSpy(navSelector, sectionSelector, options = {}) {
  const navLinks = document.querySelectorAll(`${navSelector} a[href^="#"]`);
  const sections = document.querySelectorAll(sectionSelector);
  if (!navLinks.length || !sections.length) {
    console.warn('Scroll spy: no nav links or sections found');
    return;
  }

  const offset = options.offset || 80;

  // Smooth scroll on click
  navLinks.forEach(link => {
    link.addEventListener('click', (e) => {
      e.preventDefault();
      const targetId = link.getAttribute('href').slice(1);
      const target = document.getElementById(targetId);
      if (target) {
        window.scrollTo({ top: target.offsetTop - offset, behavior: 'smooth' });
      }
    });
  });

  // Intersection observer for active state
  const observer = new IntersectionObserver((entries) => {
    entries.forEach(entry => {
      if (entry.isIntersecting) {
        navLinks.forEach(l => l.classList.remove('active'));
        const active = document.querySelector(`${navSelector} a[href="#${entry.target.id}"]`);
        if (active) active.classList.add('active');
      }
    });
  }, { rootMargin: `-${offset}px 0px -60% 0px` });

  sections.forEach(section => observer.observe(section));
  return observer;
}

// Usage: initScrollSpy('.side-nav', 'section[data-section]');


Create a draggable range slider with real-time value display

Solution:
function createRangeSlider(container, options = {}) {
  const { min = 0, max = 100, step = 1, value = 50, onChange } = options;
  container = typeof container === 'string' ? document.querySelector(container) : container;
  if (!container) throw new Error('Slider container not found');

  const wrapper = document.createElement('div');
  wrapper.className = 'range-slider';
  wrapper.style.cssText = 'display:flex;align-items:center;gap:1rem;font-family:sans-serif;';

  const input = document.createElement('input');
  input.type = 'range';
  input.min = min;
  input.max = max;
  input.step = step;
  input.value = value;
  input.style.flex = '1';

  const valueDisplay = document.createElement('span');
  valueDisplay.className = 'slider-value';
  valueDisplay.textContent = value;
  valueDisplay.style.minWidth = '3ch';
  valueDisplay.style.textAlign = 'right';
  valueDisplay.style.fontVariantNumeric = 'tabular-nums';

  input.addEventListener('input', (e) => {
    valueDisplay.textContent = e.target.value;
    if (typeof onChange === 'function') onChange(Number(e.target.value));
  });

  wrapper.appendChild(input);
  wrapper.appendChild(valueDisplay);
  container.appendChild(wrapper);

  return { input, valueDisplay, getValue: () => Number(input.value) };
}

// Usage:
// createRangeSlider('#slider-box', {
//   min: 0, max: 255, value: 128,
//   onChange: (v) => { document.body.style.background = `rgb(${v},${v},${v})`; }
// });


Build a color picker canvas with eyedropper and palette export

Solution:
function createColorPicker(canvasId, exportBtnId) {
  const canvas = document.getElementById(canvasId);
  const exportBtn = document.getElementById(exportBtnId);
  if (!canvas || !exportBtn) throw new Error('Color picker elements not found');

  const ctx = canvas.getContext('2d', { willReadFrequently: true });
  let isDragging = false;
  const palette = new Set();

  // Draw a hue-saturation gradient
  function drawGradient() {
    const w = canvas.width;
    const h = canvas.height;
    for (let x = 0; x < w; x++) {
      const hue = (x / w) * 360;
      const grad = ctx.createLinearGradient(0, 0, 0, h);
      grad.addColorStop(0, `hsl(${hue}, 100%, 50%)`);
      grad.addColorStop(1, `hsl(${hue}, 100%, 0%)`);
      ctx.fillStyle = grad;
      ctx.fillRect(x, 0, 1, h);
    }
  }
  drawGradient();

  function pickColor(x, y) {
    const pixel = ctx.getImageData(x, y, 1, 1).data;
    const hex = '#' + [pixel[0], pixel[1], pixel[2]].map(c => c.toString(16).padStart(2, '0')).join('');
    return hex;
  }

  function handleMove(e) {
    const rect = canvas.getBoundingClientRect();
    const x = Math.min(Math.max(e.clientX - rect.left, 0), canvas.width - 1);
    const y = Math.min(Math.max(e.clientY - rect.top, 0), canvas.height - 1);
    const color = pickColor(x, y);
    canvas.style.cursor = 'crosshair';
    if (isDragging) {
      palette.add(color);
      canvas.dispatchEvent(new CustomEvent('colorpicked', { detail: { color, x, y } }));
    }
    return color;
  }

  canvas.addEventListener('mousedown', (e) => { isDragging = true; handleMove(e); });
  canvas.addEventListener('mousemove', handleMove);
  canvas.addEventListener('mouseup', () => { isDragging = false; });
  canvas.addEventListener('mouseleave', () => { isDragging = false; });

  exportBtn.addEventListener('click', () => {
    const colors = Array.from(palette);
    const blob = new Blob([JSON.stringify(colors, null, 2)], { type: 'application/json' });
    const url = URL.createObjectURL(blob);
    const a = document.createElement('a');
    a.href = url;
    a.download = 'palette.json';
    a.click();
    URL.revokeObjectURL(url);
  });

  return { canvas, palette, pickColor };
}

// Usage: createColorPicker('picker-canvas', 'export-btn');


Create a live code preview playground with iframe sandbox

Solution:
function createCodePlayground(containerSelector) {
  const container = document.querySelector(containerSelector);
  if (!container) throw new Error('Playground container not found');

  container.innerHTML = `

        <button data-lang="html">HTML</button>
        <button data-lang="css">CSS</button>
        <button data-lang="js">JS</button>
        <button data-action="run" style="margin-left:auto;">Run</button>

      <textarea class="editor" style="flex:1;resize:none;border:none;padding:1rem;background:#1e1e1e;color:#d4d4d4;font-size:14px;" spellcheck="false"></textarea>

  `;

  const editor = container.querySelector('.editor');
  const preview = container.querySelector('.preview');
  const files = { html: '
Hello World
', css: 'h1 { color: #00cec9; }', js: 'console.log("ready");' };
  let currentLang = 'html';

  editor.value = files.html;

  container.querySelectorAll('button[data-lang]').forEach(btn => {
    btn.addEventListener('click', () => {
      files[currentLang] = editor.value;
      currentLang = btn.dataset.lang;
      editor.value = files[currentLang];
    });
  });

  container.querySelector('button[data-action="run"]').addEventListener('click', () => {
    files[currentLang] = editor.value;
    const doc = `
      <!DOCTYPE html>

      ${files.html}

    `;
    preview.srcdoc = doc;
  });

  return { editor, preview, getFiles: () => ({ ...files }) };
}

// Usage: createCodePlayground('#playground');


Build a resizable split-pane layout with drag handle

Solution:
function createSplitPane(containerSelector, options = {}) {
  const container = document.querySelector(containerSelector);
  if (!container) throw new Error('Split pane container not found');

  const { direction = 'horizontal', initialRatio = 0.5, minSize = 100 } = options;
  const isHorizontal = direction === 'horizontal';

  container.style.display = 'flex';
  container.style.flexDirection = isHorizontal ? 'row' : 'column';
  container.style.height = '100%';
  container.style.overflow = 'hidden';

  const pane1 = document.createElement('div');
  pane1.className = 'pane pane-1';
  pane1.style.flex = `0 0 calc(${initialRatio * 100}% - 4px)`;
  pane1.style.overflow = 'auto';
  pane1.style.minWidth = isHorizontal ? minSize + 'px' : 'auto';
  pane1.style.minHeight = !isHorizontal ? minSize + 'px' : 'auto';

  const handle = document.createElement('div');
  handle.className = 'split-handle';
  handle.style.flex = '0 0 8px';
  handle.style.background = '#e0e0e0';
  handle.style.cursor = isHorizontal ? 'col-resize' : 'row-resize';
  handle.style.userSelect = 'none';

  const pane2 = document.createElement('div');
  pane2.className = 'pane pane-2';
  pane2.style.flex = '1 1 auto';
  pane2.style.overflow = 'auto';
  pane2.style.minWidth = isHorizontal ? minSize + 'px' : 'auto';
  pane2.style.minHeight = !isHorizontal ? minSize + 'px' : 'auto';

  container.appendChild(pane1);
  container.appendChild(handle);
  container.appendChild(pane2);

  let isDragging = false;
  const sizeProp = isHorizontal ? 'clientWidth' : 'clientHeight';

  handle.addEventListener('mousedown', (e) => {
    isDragging = true;
    document.body.style.cursor = isHorizontal ? 'col-resize' : 'row-resize';
  });

  document.addEventListener('mousemove', (e) => {
    if (!isDragging) return;
    const rect = container.getBoundingClientRect();
    const pos = isHorizontal ? e.clientX - rect.left : e.clientY - rect.top;
    const ratio = Math.max(minSize, Math.min(pos, rect[sizeProp] - minSize)) / rect[sizeProp];
    pane1.style.flex = `0 0 calc(${ratio * 100}% - 4px)`;
  });

  document.addEventListener('mouseup', () => {
    isDragging = false;
    document.body.style.cursor = '';
  });

  return { pane1, pane2, handle };
}

// Usage: createSplitPane('#editor-layout', { direction: 'horizontal', initialRatio: 0.4 });


Implement a masonry image grid with lazy loading and lightbox

Solution:
function createMasonryGallery(containerSelector, imageUrls) {
  const container = document.querySelector(containerSelector);
  if (!container) throw new Error('Gallery container not found');

  container.style.columnCount = '3';
  container.style.columnGap = '1rem';

  if (!Array.isArray(imageUrls)) throw new TypeError('imageUrls must be an array');

  // Lightbox overlay
  const lightbox = document.createElement('div');
  lightbox.style.cssText = 'position:fixed;inset:0;background:rgba(0,0,0,0.9);display:none;align-items:center;justify-content:center;z-index:1000;';
  const img = document.createElement('img');
  img.style.maxWidth = '90vw';
  img.style.maxHeight = '90vh';
  img.style.objectFit = 'contain';
  lightbox.appendChild(img);
  lightbox.addEventListener('click', () => { lightbox.style.display = 'none'; });
  document.body.appendChild(lightbox);

  imageUrls.forEach((src, i) => {
    const wrapper = document.createElement('div');
    wrapper.style.breakInside = 'avoid';
    wrapper.style.marginBottom = '1rem';

    const image = document.createElement('img');
    image.dataset.src = src;
    image.alt = `Gallery image ${i + 1}`;
    image.style.width = '100%';
    image.style.borderRadius = '8px';
    image.style.display = 'block';
    image.style.background = '#0984e3';
    image.style.minHeight = '150px';

    image.addEventListener('click', () => {
      img.src = src;
      lightbox.style.display = 'flex';
    });

    wrapper.appendChild(image);
    container.appendChild(wrapper);
  });

  // Lazy loading
  const observer = new IntersectionObserver((entries) => {
    entries.forEach(entry => {
      if (entry.isIntersecting && entry.target.dataset.src) {
        entry.target.src = entry.target.dataset.src;
        delete entry.target.dataset.src;
        observer.unobserve(entry.target);
      }
    });
  }, { rootMargin: '200px' });

  container.querySelectorAll('img[data-src]').forEach(img => observer.observe(img));
  return { container, lightbox, observer };
}

// Usage: createMasonryGallery('#gallery', ['/img/1.jpg', '/img/2.jpg']);


Create an image carousel with touch swipe and keyboard controls

Solution:
function createCarousel(containerSelector, slides) {
  const container = document.querySelector(containerSelector);
  if (!container) throw new Error('Carousel container not found');
  if (!Array.isArray(slides) || slides.length === 0) throw new Error('Slides array required');

  let current = 0;

  container.innerHTML = `

      <button class="prev" style="position:absolute;left:1rem;top:50%;transform:translateY(-50%);" aria-label="Previous slide">←</button>
      <button class="next" style="position:absolute;right:1rem;top:50%;transform:translateY(-50%);" aria-label="Next slide">→</button>

  `;

  const track = container.querySelector('.track');
  const indicators = container.querySelector('.indicators');

  slides.forEach((slide, i) => {
    const div = document.createElement('div');
    div.style.minWidth = '100%';
    div.innerHTML = slide;
    track.appendChild(div);

    const dot = document.createElement('button');
    dot.style.width = '10px';
    dot.style.height = '10px';
    dot.style.borderRadius = '50%';
    dot.style.border = 'none';
    dot.style.background = i === 0 ? '#fff' : 'rgba(255,255,255,0.4)';
    dot.addEventListener('click', () => goTo(i));
    indicators.appendChild(dot);
  });

  function goTo(index) {
    current = ((index % slides.length) + slides.length) % slides.length;
    track.style.transform = `translateX(-${current * 100}%)`;
    Array.from(indicators.children).forEach((dot, i) => {
      dot.style.background = i === current ? '#fff' : 'rgba(255,255,255,0.4)';
    });
  }

  container.querySelector('.prev').addEventListener('click', () => goTo(current - 1));
  container.querySelector('.next').addEventListener('click', () => goTo(current + 1));

  // Touch swipe
  let startX = 0;
  container.addEventListener('touchstart', (e) => { startX = e.touches[0].clientX; });
  container.addEventListener('touchend', (e) => {
    const diff = startX - e.changedTouches[0].clientX;
    if (Math.abs(diff) > 50) goTo(current + (diff > 0 ? 1 : -1));
  });

  // Keyboard
  container.setAttribute('tabindex', '0');
  container.addEventListener('keydown', (e) => {
    if (e.key === 'ArrowLeft') goTo(current - 1);
    if (e.key === 'ArrowRight') goTo(current + 1);
  });

  return { goTo, getCurrent: () => current };
}

// Usage: createCarousel('#carousel', ['', '']);


Build an infinite scroll image feed with skeleton placeholders

Solution:
function createInfiniteFeed(containerSelector, fetchPage, options = {}) {
  const container = document.querySelector(containerSelector);
  if (!container) throw new Error('Feed container not found');
  if (typeof fetchPage !== 'function') throw new TypeError('fetchPage must be a function');

  const { pageSize = 20, threshold = 300 } = options;
  let page = 1;
  let isLoading = false;
  let hasMore = true;

  function createSkeletons(count) {
    const frag = document.createDocumentFragment();
    for (let i = 0; i < count; i++) {
      const div = document.createElement('div');
      div.className = 'skeleton';
      div.style.cssText = 'height:200px;background:linear-gradient(90deg,#f0f0f0 25%,#e0e0e0 50%,#f0f0f0 75%);background-size:200% 100%;animation:shimmer 1.5s infinite;border-radius:8px;';
      frag.appendChild(div);
    }
    return frag;
  }

  // Add shimmer keyframes if not present
  if (!document.getElementById('skeleton-styles')) {
    const style = document.createElement('style');
    style.id = 'skeleton-styles';
    style.textContent = '@keyframes shimmer { 0% { background-position: 200% 0; } 100% { background-position: -200% 0; } }';
    document.head.appendChild(style);
  }

  async function loadMore() {
    if (isLoading || !hasMore) return;
    isLoading = true;
    const skeletons = createSkeletons(pageSize);
    container.appendChild(skeletons);

    try {
      const items = await fetchPage(page, pageSize);
      skeletons.remove();
      if (!items || items.length === 0) {
        hasMore = false;
        return;
      }
      items.forEach(item => container.appendChild(item));
      page++;
    } catch (err) {
      console.error('Feed load error:', err);
      skeletons.remove();
    } finally {
      isLoading = false;
    }
  }

  const sentinel = document.createElement('div');
  sentinel.style.height = '1px';
  container.appendChild(sentinel);

  const observer = new IntersectionObserver((entries) => {
    if (entries[0].isIntersecting) loadMore();
  }, { rootMargin: `${threshold}px` });
  observer.observe(sentinel);

  loadMore();
  return { loadMore, observer };
}

// Usage:
// createInfiniteFeed('#feed', async (page, size) => {
//   const res = await fetch(`/api/images?page=${page}&size=$250px`);
//   const data = await res.json();
//   return data.map(url => { const img = document.createElement('img'); img.src = url; return img; });
// });


Create a 2D canvas game loop with delta-time physics

Solution:
class GameEngine {
  constructor(canvasId, options = {}) {
    this.canvas = document.getElementById(canvasId);
    if (!this.canvas) throw new Error('Canvas not found: ' + canvasId);
    this.ctx = this.canvas.getContext('2d');
    this.entities = [];
    this.lastTime = 0;
    this.running = false;
    this.fps = 60;

    this.canvas.width = options.width || 800;
    this.canvas.height = options.height || 600;
    this.canvas.style.background = options.bg || '#fab1a0';
  }

  addEntity(entity) {
    if (!entity.update || !entity.draw) {
      throw new TypeError('Entity must have update(dt) and draw(ctx) methods');
    }
    this.entities.push(entity);
    return this;
  }

  start() {
    this.running = true;
    requestAnimationFrame((t) => this.loop(t));
  }

  stop() {
    this.running = false;
  }

  loop(timestamp) {
    if (!this.running) return;
    const dt = Math.min((timestamp - this.lastTime) / 1000, 0.05); // Cap delta
    this.lastTime = timestamp;

    this.ctx.clearRect(0, 0, this.canvas.width, this.canvas.height);

    for (const entity of this.entities) {
      entity.update(dt, this.canvas.width, this.canvas.height);
      entity.draw(this.ctx);
    }

    requestAnimationFrame((t) => this.loop(t));
  }
}

// Usage:
// const engine = new GameEngine('game-canvas', { width: 800, height: 600 });
// engine.addEntity({ update(dt, w, h) { this.x += 100 * dt; }, draw(ctx) { ctx.fillRect(this.x, 100, 20, 20); }, x: 0 });
// engine.start();


Implement AABB collision detection for rectangular game entities

Solution:
function checkAABBCollision(a, b) {
  if (!a || !b) throw new Error('Both entities required for collision check');
  return (
    a.x < b.x + b.width &&
    a.x + a.width > b.x &&
    a.y < b.y + b.height &&
    a.y + a.height > b.y
  );
}

function resolveAABBOverlap(a, b) {
  const overlapX = Math.min(a.x + a.width, b.x + b.width) - Math.max(a.x, b.x);
  const overlapY = Math.min(a.y + a.height, b.y + b.height) - Math.max(a.y, b.y);

  if (overlapX < overlapY) {
    const dir = a.x < b.x ? -1 : 1;
    a.x += (overlapX / 2) * dir;
    b.x -= (overlapX / 2) * dir;
  } else {
    const dir = a.y < b.y ? -1 : 1;
    a.y += (overlapY / 2) * dir;
    b.y -= (overlapY / 2) * dir;
  }
}

class PhysicsWorld {
  constructor() {
    this.bodies = [];
  }

  add(body) {
    if (typeof body.x !== 'number' || typeof body.y !== 'number') {
      throw new TypeError('Body must have numeric x and y properties');
    }
    this.bodies.push(body);
  }

  step() {
    for (let i = 0; i < this.bodies.length; i++) {
      for (let j = i + 1; j < this.bodies.length; j++) {
        if (checkAABBCollision(this.bodies[i], this.bodies[j])) {
          resolveAABBOverlap(this.bodies[i], this.bodies[j]);
          if (this.bodies[i].onCollision) this.bodies[i].onCollision(this.bodies[j]);
          if (this.bodies[j].onCollision) this.bodies[j].onCollision(this.bodies[i]);
        }
      }
    }
  }
}

// Usage:
// const world = new PhysicsWorld();
// world.add({ x: 0, y: 0, width: 32, height: 32, onCollision(other) { console.log('hit!'); } });
// world.step();


Build a sprite animation system with frame clipping and playback controls

Solution:
class SpriteAnimator {
  constructor(image, frameWidth, frameHeight, frameCount) {
    if (!(image instanceof HTMLImageElement)) throw new TypeError('Expected HTMLImageElement');
    this.image = image;
    this.frameWidth = frameWidth;
    this.frameHeight = frameHeight;
    this.frameCount = frameCount;
    this.currentFrame = 0;
    this.elapsed = 0;
    this.fps = 10;
    this.playing = true;
    this.loop = true;
  }

  update(dt) {
    if (!this.playing) return;
    this.elapsed += dt;
    const frameDuration = 1 / this.fps;
    if (this.elapsed >= frameDuration) {
      this.elapsed -= frameDuration;
      this.currentFrame++;
      if (this.currentFrame >= this.frameCount) {
        if (this.loop) this.currentFrame = 0;
        else { this.currentFrame = this.frameCount - 1; this.playing = false; }
      }
    }
  }

  draw(ctx, x, y, options = {}) {
    const sx = (this.currentFrame * this.frameWidth) % this.image.width;
    const sy = Math.floor((this.currentFrame * this.frameWidth) / this.image.width) * this.frameHeight;
    const scale = options.scale || 1;
    ctx.drawImage(
      this.image,
      sx, sy, this.frameWidth, this.frameHeight,
      x, y, this.frameWidth * scale, this.frameHeight * scale
    );
  }

  play() { this.playing = true; }
  pause() { this.playing = false; }
  reset() { this.currentFrame = 0; this.elapsed = 0; }
  setFrame(index) { this.currentFrame = Math.max(0, Math.min(index, this.frameCount - 1)); }
}

// Usage:
// const img = new Image();
// img.src = '/sprites/player.png';
// img.onload = () => {
//   const anim = new SpriteAnimator(img, 32, 32, 8);
//   // In game loop: anim.update(dt); anim.draw(ctx, 100, 100);
// };


Implement a tilemap renderer with camera scrolling and culling

Solution:
class TilemapRenderer {
  constructor(canvasId, tileSize = 32) {
    this.canvas = document.getElementById(canvasId);
    if (!this.canvas) throw new Error('Canvas not found');
    this.ctx = this.canvas.getContext('2d');
    this.tileSize = tileSize;
    this.camera = { x: 0, y: 0 };
    this.tiles = []; // 2D array of tile IDs
    this.tileset = new Map(); // ID -> color or image
  }

  loadMap(tiles) {
    if (!Array.isArray(tiles) || !tiles.every(row => Array.isArray(row))) {
      throw new TypeError('tiles must be a 2D array');
    }
    this.tiles = tiles;
  }

  registerTile(id, renderable) {
    this.tileset.set(id, renderable);
  }

  setCamera(x, y) {
    this.camera.x = x;
    this.camera.y = y;
  }

  render() {
    const cols = Math.ceil(this.canvas.width / this.tileSize) + 1;
    const rows = Math.ceil(this.canvas.height / this.tileSize) + 1;
    const startCol = Math.floor(this.camera.x / this.tileSize);
    const startRow = Math.floor(this.camera.y / this.tileSize);

    for (let r = 0; r < rows; r++) {
      for (let c = 0; c < cols; c++) {
        const tileRow = startRow + r;
        const tileCol = startCol + c;
        if (tileRow < 0 || tileRow >= this.tiles.length) continue;
        if (tileCol < 0 || tileCol >= this.tiles[tileRow].length) continue;

        const tileId = this.tiles[tileRow][tileCol];
        const screenX = c * this.tileSize - (this.camera.x % this.tileSize);
        const screenY = r * this.tileSize - (this.camera.y % this.tileSize);

        const renderable = this.tileset.get(tileId);
        if (typeof renderable === 'string') {
          this.ctx.fillStyle = renderable;
          this.ctx.fillRect(screenX, screenY, this.tileSize, this.tileSize);
        } else if (renderable instanceof HTMLImageElement) {
          this.ctx.drawImage(renderable, screenX, screenY, this.tileSize, this.tileSize);
        }
      }
    }
  }
}

// Usage:
// const renderer = new TilemapRenderer('game-canvas', 32);
// renderer.loadMap([[0,0,1],[0,1,1],[1,1,1]]);
// renderer.registerTile(0, '#fab1a0');
// renderer.registerTile(1, '#00b894');
// renderer.setCamera(100, 50);
// renderer.render();


Create a particle explosion effect on canvas for game feedback

Solution:
class ParticleSystem {
  constructor() {
    this.particles = [];
  }

  emit(x, y, options = {}) {
    const {
      count = 5,
      speed = 0.03,
      life = 1.0,
      colors = ['#4ecdc4', '#e17055', '#6c5ce7'],
      size = 4,
      gravity = 200
    } = options;

    for (let i = 0; i < count; i++) {
      const angle = (Math.PI * 2 * i) / count + (Math.random() - 0.5) * 0.5;
      const velocity = speed * (0.5 + Math.random() * 0.5);
      this.particles.push({
        x, y,
        vx: Math.cos(angle) * velocity,
        vy: Math.sin(angle) * velocity,
        life,
        maxLife: life,
        color: colors[Math.floor(Math.random() * colors.length)],
        size: size * (0.5 + Math.random()),
        gravity
      });
    }
  }

  update(dt) {
    for (let i = this.particles.length - 1; i >= 0; i--) {
      const p = this.particles[i];
      p.x += p.vx * dt;
      p.y += p.vy * dt;
      p.vy += p.gravity * dt;
      p.life -= dt;
      if (p.life <= 0) this.particles.splice(i, 1);
    }
  }

  draw(ctx) {
    for (const p of this.particles) {
      const alpha = Math.max(0, p.life / p.maxLife);
      ctx.globalAlpha = alpha;
      ctx.fillStyle = p.color;
      ctx.beginPath();
      ctx.arc(p.x, p.y, p.size * alpha, 0, Math.PI * 2);
      ctx.fill();
    }
    ctx.globalAlpha = 1;
  }
}

// Usage:
// const particles = new ParticleSystem();
// particles.emit(400, 300, { count: 30, speed: 150, colors: ['#a29bfe', '#fd79a8', '#00b894'] });
// // In game loop: particles.update(dt); particles.draw(ctx);


Create a Three.js scene with a rotating colored cube

Solution:
import * as THREE from 'three';

function createCubeScene(containerId = 'canvas-container') {
  const container = document.getElementById(containerId);
  if (!container) throw new Error('Container not found: ' + containerId);

  const scene = new THREE.Scene();
  scene.background = new THREE.Color('#4ecdc4');

  const camera = new THREE.PerspectiveCamera(75, container.clientWidth / container.clientHeight, 0.1, 1000);
  camera.position.z = 5;

  const renderer = new THREE.WebGLRenderer({ antialias: true });
  renderer.setSize(container.clientWidth, container.clientHeight);
  renderer.setPixelRatio(window.devicePixelRatio);
  container.appendChild(renderer.domElement);

  const geometry = new THREE.BoxGeometry(1, 1, 1);
  const material = new THREE.MeshStandardMaterial({ color: '#55efc4', roughness: 0.3, metalness: 0.1 });
  const cube = new THREE.Mesh(geometry, material);
  scene.add(cube);

  const light = new THREE.DirectionalLight(0xffffff, 1);
  light.position.set(5, 5, 5);
  scene.add(light);
  scene.add(new THREE.AmbientLight(0x404040));

  function animate() {
    requestAnimationFrame(animate);
    cube.rotation.x += 0.03;
    cube.rotation.y += 0.03;
    renderer.render(scene, camera);
  }
  animate();

  window.addEventListener('resize', () => {
    camera.aspect = container.clientWidth / container.clientHeight;
    camera.updateProjectionMatrix();
    renderer.setSize(container.clientWidth, container.clientHeight);
  });

  return { scene, camera, renderer, cube };
}

// Usage: createCubeScene();


Load a GLTF 3D model in Three.js with orbit controls

Solution:
import * as THREE from 'three';
import { GLTFLoader } from 'three/examples/jsm/loaders/GLTFLoader.js';
import { OrbitControls } from 'three/examples/jsm/controls/OrbitControls.js';

async function loadModel(url, containerId = 'canvas-container') {
  const container = document.getElementById(containerId);
  if (!container) throw new Error('Container not found');

  const scene = new THREE.Scene();
  scene.background = new THREE.Color('#e84393');
  scene.fog = new THREE.Fog('#e84393', 10, 50);

  const camera = new THREE.PerspectiveCamera(45, container.clientWidth / container.clientHeight, 0.1, 100);
  camera.position.set(0, 2, 5);

  const renderer = new THREE.WebGLRenderer({ antialias: true });
  renderer.setSize(container.clientWidth, container.clientHeight);
  renderer.shadowMap.enabled = true;
  container.appendChild(renderer.domElement);

  const controls = new OrbitControls(camera, renderer.domElement);
  controls.enableDamping = true;
  controls.dampingFactor = 0.05;

  scene.add(new THREE.AmbientLight(0xffffff, 0.5));
  const dirLight = new THREE.DirectionalLight(0xffffff, 1);
  dirLight.position.set(5, 10, 7);
  dirLight.castShadow = true;
  scene.add(dirLight);

  const loader = new GLTFLoader();
  try {
    const gltf = await loader.loadAsync(url);
    const model = gltf.scene;
    model.traverse(child => { if (child.isMesh) child.castShadow = true; });
    scene.add(model);
  } catch (err) {
    console.error('Failed to load model:', err);
    throw err;
  }

  function animate() {
    requestAnimationFrame(animate);
    controls.update();
    renderer.render(scene, camera);
  }
  animate();

  return { scene, camera, controls };
}

// Usage: loadModel('/models/character.glb');


Create a particle system in Three.js with random motion

Solution:
import * as THREE from 'three';

function createParticles(count = 15, containerId = 'canvas-container') {
  const container = document.getElementById(containerId);
  if (!container) throw new Error('Container not found');

  const scene = new THREE.Scene();
  const camera = new THREE.PerspectiveCamera(75, container.clientWidth / container.clientHeight, 0.1, 1000);
  camera.position.z = 30;

  const renderer = new THREE.WebGLRenderer({ antialias: true, alpha: true });
  renderer.setSize(container.clientWidth, container.clientHeight);
  container.appendChild(renderer.domElement);

  const geometry = new THREE.BufferGeometry();
  const positions = new Float32Array(count * 3);
  const velocities = [];

  for (let i = 0; i < count; i++) {
    positions[i * 3] = (Math.random() - 0.5) * 50;
    positions[i * 3 + 1] = (Math.random() - 0.5) * 50;
    positions[i * 3 + 2] = (Math.random() - 0.5) * 50;
    velocities.push({
      x: (Math.random() - 0.5) * 0.015,
      y: (Math.random() - 0.5) * 0.015,
      z: (Math.random() - 0.5) * 0.015
    });
  }

  geometry.setAttribute('position', new THREE.BufferAttribute(positions, 3));
  const material = new THREE.PointsMaterial({ color: '#45b7d1', size: 0.5, transparent: true, opacity: 0.8 });
  const particles = new THREE.Points(geometry, material);
  scene.add(particles);

  function animate() {
    requestAnimationFrame(animate);
    const pos = geometry.attributes.position.array;
    for (let i = 0; i < count; i++) {
      pos[i * 3] += velocities[i].x;
      pos[i * 3 + 1] += velocities[i].y;
      pos[i * 3 + 2] += velocities[i].z;
      if (Math.abs(pos[i * 3]) > 25) velocities[i].x *= -1;
      if (Math.abs(pos[i * 3 + 1]) > 25) velocities[i].y *= -1;
      if (Math.abs(pos[i * 3 + 2]) > 25) velocities[i].z *= -1;
    }
    geometry.attributes.position.needsUpdate = true;
    renderer.render(scene, camera);
  }
  animate();

  return { scene, particles, renderer };
}

// Usage: createParticles(200);


Create a reflective sphere with environment mapping in Three.js

Solution:
import * as THREE from 'three';

function createReflectiveSphere(containerId = 'canvas-container') {
  const container = document.getElementById(containerId);
  if (!container) throw new Error('Container not found');

  const scene = new THREE.Scene();
  const camera = new THREE.PerspectiveCamera(75, container.clientWidth / container.clientHeight, 0.1, 1000);
  camera.position.z = 3;

  const renderer = new THREE.WebGLRenderer({ antialias: true });
  renderer.setSize(container.clientWidth, container.clientHeight);
  renderer.toneMapping = THREE.ACESFilmicToneMapping;
  container.appendChild(renderer.domElement);

  const pmremGenerator = new THREE.PMREMGenerator(renderer);
  const envScene = new THREE.Scene();
  envScene.background = new THREE.Color('#00b894');
  envScene.add(new THREE.Mesh(
    new THREE.SphereGeometry(10, 32, 32),
    new THREE.MeshBasicMaterial({ color: '#e84393', side: THREE.BackSide })
  ));
  const envMap = pmremGenerator.fromScene(envScene).texture;

  const geometry = new THREE.SphereGeometry(1, 64, 64);
  const material = new THREE.MeshPhysicalMaterial({
    color: '#96ceb4',
    metalness: 1.0,
    roughness: 0.1,
    envMap,
    envMapIntensity: 1.0
  });
  const sphere = new THREE.Mesh(geometry, material);
  scene.add(sphere);

  function animate() {
    requestAnimationFrame(animate);
    sphere.rotation.y += 0.005;
    renderer.render(scene, camera);
  }
  animate();

  return { scene, sphere, renderer };
}

// Usage: createReflectiveSphere();


Build a Three.js first-person camera controller with WASD movement

Solution:
import * as THREE from 'three';

function createFPSController(containerId = 'canvas-container') {
  const container = document.getElementById(containerId);
  if (!container) throw new Error('Container not found');

  const scene = new THREE.Scene();
  scene.background = new THREE.Color('#0984e3');

  const camera = new THREE.PerspectiveCamera(75, container.clientWidth / container.clientHeight, 0.1, 1000);
  camera.position.y = 1.7;

  const renderer = new THREE.WebGLRenderer({ antialias: true });
  renderer.setSize(container.clientWidth, container.clientHeight);
  container.appendChild(renderer.domElement);

  // Floor
  const floor = new THREE.Mesh(
    new THREE.PlaneGeometry(50, 50),
    new THREE.MeshStandardMaterial({ color: '#ff6b6b' })
  );
  floor.rotation.x = -Math.PI / 2;
  floor.receiveShadow = true;
  scene.add(floor);

  scene.add(new THREE.AmbientLight(0x404040));
  const dirLight = new THREE.DirectionalLight(0xffffff, 0.8);
  dirLight.position.set(5, 10, 5);
  scene.add(dirLight);

  const keys = { w: false, a: false, s: false, d: false };
  const velocity = new THREE.Vector3();
  const direction = new THREE.Vector3();

  document.addEventListener('keydown', (e) => { if (keys.hasOwnProperty(e.key.toLowerCase())) keys[e.key.toLowerCase()] = true; });
  document.addEventListener('keyup', (e) => { if (keys.hasOwnProperty(e.key.toLowerCase())) keys[e.key.toLowerCase()] = false; });

  container.addEventListener('click', () => container.requestPointerLock());
  document.addEventListener('mousemove', (e) => {
    if (document.pointerLockElement === container) {
      camera.rotation.y -= e.movementX * 0.002;
      camera.rotation.x -= e.movementY * 0.002;
      camera.rotation.x = Math.max(-Math.PI / 2, Math.min(Math.PI / 2, camera.rotation.x));
    }
  });

  const clock = new THREE.Clock();
  function animate() {
    requestAnimationFrame(animate);
    const delta = clock.getDelta();
    velocity.x -= velocity.x * 10 * delta;
    velocity.z -= velocity.z * 10 * delta;
    direction.z = Number(keys.w) - Number(keys.s);
    direction.x = Number(keys.a) - Number(keys.d);
    direction.normalize();
    if (keys.w || keys.s) velocity.z -= direction.z * 40 * delta;
    if (keys.a || keys.d) velocity.x -= direction.x * 40 * delta;
    camera.translateX(-velocity.x * delta);
    camera.translateZ(-velocity.z * delta);
    camera.position.y = 1.7;
    renderer.render(scene, camera);
  }
  animate();

  return { scene, camera, renderer };
}

// Usage: createFPSController();


Create an animated torus knot with wireframe overlay in Three.js

Solution:
import * as THREE from 'three';

function createTorusKnot(containerId = 'canvas-container') {
  const container = document.getElementById(containerId);
  if (!container) throw new Error('Container not found');

  const scene = new THREE.Scene();
  scene.background = new THREE.Color('#96ceb4');

  const camera = new THREE.PerspectiveCamera(75, container.clientWidth / container.clientHeight, 0.1, 1000);
  camera.position.z = 5;

  const renderer = new THREE.WebGLRenderer({ antialias: true });
  renderer.setSize(container.clientWidth, container.clientHeight);
  container.appendChild(renderer.domElement);

  const geometry = new THREE.TorusKnotGeometry(1, 0.3, 100, 16);
  const material = new THREE.MeshStandardMaterial({ color: '#ffeaa7', roughness: 0.4, metalness: 0.3 });
  const torus = new THREE.Mesh(geometry, material);
  scene.add(torus);

  const wireGeo = new THREE.WireframeGeometry(geometry);
  const wireMat = new THREE.LineBasicMaterial({ color: '#4ecdc4' });
  const wireframe = new THREE.LineSegments(wireGeo, wireMat);
  torus.add(wireframe);

  scene.add(new THREE.AmbientLight(0x404040));
  const pointLight = new THREE.PointLight(0xffffff, 1, 100);
  pointLight.position.set(2, 3, 4);
  scene.add(pointLight);

  function animate() {
    requestAnimationFrame(animate);
    torus.rotation.x += 0.01;
    torus.rotation.y += 0.01 * 0.7;
    renderer.render(scene, camera);
  }
  animate();

  return { scene, torus, renderer };
}

// Usage: createTorusKnot();


Raycast from mouse to detect 3D object clicks in Three.js

Solution:
import * as THREE from 'three';

function setupRaycasting(scene, camera, renderer, onIntersect) {
  const raycaster = new THREE.Raycaster();
  const mouse = new THREE.Vector2();

  renderer.domElement.addEventListener('click', (event) => {
    const rect = renderer.domElement.getBoundingClientRect();
    mouse.x = ((event.clientX - rect.left) / rect.width) * 2 - 1;
    mouse.y = -((event.clientY - rect.top) / rect.height) * 2 + 1;

    raycaster.setFromCamera(mouse, camera);
    const intersects = raycaster.intersectObjects(scene.children, true);

    if (intersects.length > 0) {
      const hit = intersects[0];
      console.log('Clicked:', hit.object.name || hit.object.uuid);
      if (typeof onIntersect === 'function') onIntersect(hit);
    }
  });
}

// Usage example:
// const mesh = new THREE.Mesh(geometry, material);
// mesh.name = 'clickable-box';
// scene.add(mesh);
// setupRaycasting(scene, camera, renderer, (hit) => {
//   hit.object.material.color.setHex(Math.random() * 0xffffff);
// });


Build a responsive CSS grid layout with auto-fit columns

Solution:
/* Responsive grid layout */
.grid-container {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(50%, 1fr));
  gap: 1.5rem;
  padding: 2rem;
  max-width: 1200px;
  margin: 0 auto;
}

.grid-item {
  background: #4ecdc4;
  border-radius: 12px;
  padding: 1.5rem;
  box-shadow: 0 4px 6px rgba(0,0,0,0.1);
  transition: transform 0.2s ease, box-shadow 0.2s ease;
}

.grid-item:hover {
  transform: translateY(-4px);
  box-shadow: 0 12px 24px rgba(0,0,0,0.15);
}

@media (max-width: 600px) {
  .grid-container {
    grid-template-columns: 1fr;
    padding: 1rem;
  }
}


Create a sticky navigation bar that changes style on scroll

Solution:
/* Sticky nav styles */
.nav-bar {
  position: sticky;
  top: 0;
  z-index: 1000;
  background: transparent;
  padding: 1rem 2rem;
  transition: background 0.3s ease, box-shadow 0.3s ease;
}

.nav-bar.scrolled {
  background: rgba(255, 255, 255, 0.95);
  backdrop-filter: blur(10px);
  box-shadow: 0 2px 10px rgba(0,0,0,0.1);
}

/* JavaScript */
function initStickyNav(navSelector = '.nav-bar') {
  const nav = document.querySelector(navSelector);
  if (!nav) throw new Error('Nav element not found');

  function onScroll() {
    if (window.scrollY > 50) {
      nav.classList.add('scrolled');
    } else {
      nav.classList.remove('scrolled');
    }
  }

  window.addEventListener('scroll', onScroll, { passive: true });
  onScroll(); // Initialize state
  return nav;
}

// Usage: initStickyNav();


Implement debounced search input with fetch API

Solution:
async function debouncedSearch(inputSelector, endpoint, renderFn, delay = 300) {
  const input = document.querySelector(inputSelector);
  if (!input) throw new Error('Input element not found');

  let timeoutId = null;
  let controller = null;

  input.addEventListener('input', (e) => {
    const query = e.target.value.trim();
    clearTimeout(timeoutId);
    if (controller) controller.abort();

    if (!query) {
      renderFn([]);
      return;
    }

    timeoutId = setTimeout(async () => {
      controller = new AbortController();
      try {
        const res = await fetch(`${endpoint}?q=${encodeURIComponent(query)}`, {
          signal: controller.signal
        });
        if (!res.ok) throw new Error(`HTTP ${res.status}`);
        const data = await res.json();
        renderFn(data);
      } catch (err) {
        if (err.name !== 'AbortError') {
          console.error('Search failed:', err);
          renderFn([], err);
        }
      }
    }, delay);
  });
}

// Usage:
// debouncedSearch('#search', '/api/search', (results, err) => {
//   if (err) return showError(err);
//   updateDOM(results);
// });


Create a CSS-only modal with backdrop blur and focus trap

Solution:
/* Modal styles */
.modal-overlay {
  position: fixed;
  inset: 0;
  background: rgba(0, 0, 0, 0.5);
  backdrop-filter: blur(4px);
  display: flex;
  align-items: center;
  justify-content: center;
  opacity: 0;
  visibility: hidden;
  transition: opacity 0.3s ease, visibility 0.3s ease;
}

.modal-overlay.active {
  opacity: 1;
  visibility: visible;
}

.modal-content {
  background: white;
  border-radius: 16px;
  padding: 2rem;
  max-width: 500px;
  width: 90%;
  transform: scale(0.9);
  transition: transform 0.3s ease;
  box-shadow: 0 20px 60px rgba(0,0,0,0.3);
}

.modal-overlay.active .modal-content {
  transform: scale(1);
}

/* JavaScript for focus trap and keyboard */
function initModal(triggerSelector, modalSelector) {
  const trigger = document.querySelector(triggerSelector);
  const modal = document.querySelector(modalSelector);
  if (!trigger || !modal) throw new Error('Modal elements not found');

  const content = modal.querySelector('.modal-content');
  const focusables = content.querySelectorAll('button, [href], input, select, textarea, [tabindex]:not([tabindex="-1"])');

  function open() {
    modal.classList.add('active');
    (focusables[0] || content).focus();
    document.addEventListener('keydown', onKey);
  }

  function close() {
    modal.classList.remove('active');
    document.removeEventListener('keydown', onKey);
    trigger.focus();
  }

  function onKey(e) {
    if (e.key === 'Escape') close();
    if (e.key === 'Tab' && focusables.length > 0) {
      const first = focusables[0];
      const last = focusables[focusables.length - 1];
      if (e.shiftKey && document.activeElement === first) {
        e.preventDefault();
        last.focus();
      } else if (!e.shiftKey && document.activeElement === last) {
        e.preventDefault();
        first.focus();
      }
    }
  }

  trigger.addEventListener('click', open);
  modal.addEventListener('click', (e) => { if (e.target === modal) close(); });

  return { open, close };
}

// Usage: initModal('#open-modal', '#my-modal');