Modern HTML Patterns

Progressive enhancement, graceful degradation, and modern features.

Overview

Modern HTML patterns ensure compatibility while leveraging new features.

Key Concepts

• Progressive Enhancement — Base experience for all browsers
• Graceful Degradation — Enhanced experience for modern browsers
• Feature Detection — Check browser support
• Polyfills — Add missing features
• Cutting Edge — Use latest features with fallbacks

Code Examples

<script>
function supportsWebP() {
  return new Promise(resolve => {
    const img = new Image();
    img.onload = () => resolve(true);
    img.onerror = () => resolve(false);
    img.src = 'data:image/webp;base64,UklGRh4AAABXRUJQVlA4TBEAAAAvAAAAAAfQ//73v/+BiTvdCg==';
  });
}

function supportsWebPAsync() {
  return new Promise(resolve => {
    const canvas = document.createElement('canvas');
    resolve(canvas.toDataURL('image/webp').indexOf('data:image/webp') === 0);
  });
}

// Modern HTML features with fallbacks
document.addEventListener('DOMContentLoaded', () => {
  // Dialog element support
  if (!HTMLDialogElement) {
    const dialog = document.querySelector('dialog');
    dialog.showModal = () => { dialog.open = true; };
    dialog.close = () => { dialog.open = false; };
  }
  
  // IntersectionObserver support
  if (!('IntersectionObserver' in window)) {
    // Fallback: load all lazy images immediately
    document.querySelectorAll('img[loading="lazy"]').forEach(img => {
      img.src = img.dataset.src;
    });
  }
  
  // Web Animations API
  if (!Element.prototype.animate) {
    // Fallback: use CSS transitions
    document.querySelectorAll('[data-animate]').forEach(el => {
      el.classList.add('animate-fallback');
    });
  }
});
</script>


<noscript>
  <style>
    .js-only { display: none !important; }
    .noscript-message { display: block; padding: 1rem; background: #fff3cd; }
  </style>
  <div class="noscript-message">
    JavaScript is required for the best experience.
  </div>
</noscript>


<picture>
  <source srcset="image.avif" type="image/avif">
  <source srcset="image.webp" type="image/webp">
  <img src="image.jpg" alt="Description" loading="lazy">
</picture>


<form>
  <input type="email" required placeholder="Email">
  <input type="search" placeholder="Search..." increment>
  <input type="color" value="#007bff">
  <input type="date">
  <button type="submit">Submit</button>
</form>

<style>
/* Modern CSS with fallbacks */
.container {
  display: flex;
  display: -webkit-box; /* Safari */
  display: -ms-flexbox; /* IE */
  
  gap: 1rem;
  -webkit-gap: 1rem; /* Safari */
}

/* Container queries */
.card {
  container-type: inline-size;
}

@container (min-width: 400px) {
  .card-content {
    display: flex;
  }
}

/* :has() selector */
.form-group:has(:invalid) {
  border-color: red;
}

/* Scroll-driven animations */
@keyframes reveal {
  from { opacity: 0; transform: translateY(20px); }
  to { opacity: 1; transform: translateY(0); }
}

.reveal {
  animation: reveal linear both;
  animation-timeline: view();
  animation-range: entry 0% cover 40%;
}
</style>

Practice

Build a progressively enhanced page that works without JavaScript.