Skip to main content

CSS @support

Polyfills allow you to implement forward compatibility in your projects, ensuring that even users on older or less capable browsers can access new features. This is crucial for maintaining a high-quality user experience across diverse user bases, which is often a key concern in large-scale or complex projects.

What is a Polyfill?​

A polyfill is a piece of code (usually JavaScript) that provides the technology that you, the developer, expect the browser to provide natively. In the context of CSS, a polyfill would enable the use of a CSS feature that is not natively supported by a browser.

How Does It Work?​

A CSS polyfill typically uses JavaScript to detect if a CSS feature is missing and then emulates it. The polyfill script runs after the page has loaded, reads the CSS to find out which features it needs to emulate, and then dynamically updates the DOM to approximate those features.

Common Examples​

  1. Flexbox Polyfill: Older browsers that don't support Flexbox can use a polyfill to approximate Flexbox layout.

  2. CSS Grid Polyfill: For browsers that don't support CSS Grid, a polyfill can simulate grid layout features.

  3. CSS Variables Polyfill: For older browsers that don't support CSS custom properties (variables), a polyfill can provide similar functionality.

Best Practices​

  • Conditional Loading: Load polyfills only when necessary. Use feature detection to determine if a polyfill is needed.

    if (!('grid' in document.body.style)) {
      // Load CSS Grid polyfill
    }

  • Performance: Be mindful of the performance impact. Polyfills add extra JavaScript, which can slow down your site, especially on mobile or slower connections.

  • Fallbacks: Always provide a basic fallback experience in your CSS for browsers where JavaScript is disabled or fails to load.

  • Up-to-Date: Keep your polyfills updated. As browsers evolve, you may find that you no longer need certain polyfills.

  • Testing: Thoroughly test the polyfill in various browsers to ensure it provides the desired functionality without causing other issues.

When to Use Polyfills​

  • Legacy Support: When you need to support older browsers but want to use newer CSS features.

  • Progressive Enhancement: When you want to use cutting-edge features without alienating users on older browsers.

  • Cross-Browser Compatibility: When a feature is supported in most browsers but not all.