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A fast & lightweight polyfill for min/max-width CSS3 Media Queries (for IE 6-8, and more)

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Quick Overview

Respond is a lightweight JavaScript library designed to enable responsive web design in browsers that don't support CSS3 Media Queries, particularly Internet Explorer 6-8. It allows developers to create responsive layouts that work across a wide range of devices and browsers, including older ones.

Pros

  • Enables responsive design in older browsers
  • Lightweight and fast
  • Easy to implement
  • Open-source and well-maintained

Cons

  • Limited to polyfilling CSS3 Media Queries
  • May not be necessary for projects not supporting older browsers
  • Requires JavaScript to be enabled
  • Potential performance impact on older devices

Code Examples

  1. Basic usage:
<script src="respond.min.js"></script>

This code snippet shows how to include Respond.js in your HTML file.

  1. Customizing the breakpoints:
Respond.mediaQueriesSupported = function() {
    return false; // Force Respond.js to run even if media queries are supported
};

This example demonstrates how to force Respond.js to run even if the browser supports media queries.

  1. Excluding specific stylesheets:
<link href="styles.css" rel="stylesheet" data-no-respond>

This code shows how to exclude a specific stylesheet from being processed by Respond.js.

Getting Started

To use Respond.js in your project, follow these steps:

  1. Download the respond.min.js file from the GitHub repository.
  2. Include the script in your HTML file, preferably just before the closing </body> tag:
<script src="path/to/respond.min.js"></script>
  1. Ensure your CSS file with media queries is properly linked in your HTML:
<link rel="stylesheet" href="styles.css">
  1. That's it! Respond.js will now enable responsive design in older browsers that don't support CSS3 Media Queries.

Competitor Comparisons

slightlyoff logo

cassowary.js

1,696

Cassowary/JS, better, faster, future-ready

Pros of Cassowary.js

  • Implements the Cassowary constraint solving algorithm, allowing for complex layout calculations
  • Supports a wide range of constraint types, including equality and inequality constraints
  • Can be used for various applications beyond responsive design, such as UI layout and animation

Cons of Cassowary.js

  • More complex to use and implement compared to Respond's straightforward media query approach
  • Requires a deeper understanding of constraint-based programming
  • May have higher performance overhead for simpler responsive design tasks

Code Comparison

Respond:

@media screen and (min-width: 480px) {
  .element {
    width: 60%;
  }
}

Cassowary.js:

var solver = new c.SimplexSolver();
var width = new c.Variable({name: "width"});
solver.addConstraint(new c.Inequality(width, c.GEQ, 480));
solver.addConstraint(new c.Equation(width, new c.Expression(0.6, screenWidth)));

Summary

Respond is a lightweight polyfill for min/max-width CSS3 media queries, focusing on responsive design for older browsers. Cassowary.js, on the other hand, is a more powerful constraint solving library that can be applied to various layout problems, including responsive design. While Cassowary.js offers more flexibility and capabilities, it comes with a steeper learning curve and potentially higher complexity for simple responsive design tasks.

filamentgroup logo

Southstreet

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Pros of Southstreet

  • More comprehensive responsive design toolkit
  • Includes additional features like responsive images and font loading
  • Actively maintained with recent updates

Cons of Southstreet

  • Larger file size and potentially more complex implementation
  • Steeper learning curve due to additional features
  • May include unnecessary components for simpler projects

Code Comparison

Respond:

function respond(breakpoint) {
  if (window.matchMedia(breakpoint).matches) {
    // Apply styles for this breakpoint
  }
}

Southstreet:

$('.responsive-element').southstreet({
  breakpoints: {
    small: '(max-width: 30em)',
    medium: '(min-width: 30.0625em) and (max-width: 50em)',
    large: '(min-width: 50.0625em)'
  },
  // Additional configuration options
});

Both repositories aim to improve responsive web design, but Southstreet offers a more feature-rich solution with additional tools for managing responsive images, fonts, and other elements. Respond focuses primarily on providing a lightweight polyfill for min/max-width CSS3 Media Queries in older browsers.

Southstreet may be better suited for larger projects requiring a comprehensive responsive design toolkit, while Respond might be preferable for simpler implementations or when targeting older browsers with minimal overhead.

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Pros of Polka

  • Lightweight and fast Express-like web server framework for Node.js
  • Supports middleware and routing similar to Express
  • Minimal overhead and excellent performance

Cons of Polka

  • Less mature and smaller community compared to Respond
  • Fewer built-in features and may require additional plugins for some functionality

Code Comparison

Polka:

const polka = require('polka');

polka()
  .get('/', (req, res) => {
    res.end('Hello world!');
  })
  .listen(3000);

Respond:

// Respond.js
if (!window.matchMedia('(min-width: 600px)').matches) {
  // Load narrow styles
  loadCSS('narrow.css');
}

Key Differences

  • Polka is a server-side framework, while Respond is a client-side library
  • Polka focuses on building web servers, while Respond handles responsive design
  • Polka is more versatile for general web development, while Respond specifically targets CSS and media queries

Use Cases

  • Polka: Building lightweight and fast web servers or APIs
  • Respond: Implementing responsive design patterns in legacy browsers

Community and Maintenance

  • Polka: Active development, growing community
  • Respond: Less active, primarily used for legacy browser support
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unfetch

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🐕 Bare minimum 500b fetch polyfill.

Pros of unfetch

  • Lightweight and minimal (only ~500 bytes gzipped)
  • Modern fetch API polyfill for browsers
  • Supports both Node.js and browser environments

Cons of unfetch

  • Limited functionality compared to full-featured libraries
  • May require additional configuration for complex use cases
  • Less suitable for older browser support

Code Comparison

unfetch:

import unfetch from 'unfetch';

unfetch('/api/data')
  .then(r => r.json())
  .then(data => console.log(data));

Respond:

// Respond.js doesn't have a direct equivalent for API fetching
// It's primarily used for media query polyfilling in older browsers

Key Differences

  • Purpose: unfetch is a fetch API polyfill, while Respond is a media query polyfill for older browsers
  • Size: unfetch is significantly smaller (500 bytes) compared to Respond (4KB)
  • Functionality: unfetch focuses on network requests, Respond on responsive design support
  • Target audience: unfetch is for modern web applications, Respond for legacy browser support

Use Cases

unfetch is ideal for:

  • Modern web applications requiring a lightweight fetch polyfill
  • Projects targeting newer browsers with occasional legacy support

Respond is better suited for:

  • Legacy projects supporting older versions of Internet Explorer
  • Websites requiring responsive design support in outdated browsers
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preact

37,416

⚛️ Fast 3kB React alternative with the same modern API. Components & Virtual DOM.

Pros of Preact

  • Modern, lightweight alternative to React with a smaller bundle size
  • Active development and community support
  • Compatible with most React libraries and tools

Cons of Preact

  • Smaller ecosystem compared to React
  • May require additional configuration for some React-specific features

Code Comparison

Respond:

Respond.ajax = function( url, callback ) {
  var req = xmlHttp();
  if (!req){
    return;
  }
  req.open( "GET", url, true );
  req.onreadystatechange = function () {
    if ( req.readyState != 4 || req.status != 200 && req.status != 304 ){
      return;
    }
    callback( req.responseText );
  }
  if ( req.readyState == 4 ){
    return;
  }
  req.send( null );
};

Preact:

import { h, render } from 'preact';

function App() {
  return <h1>Hello, World!</h1>;
}

render(<App />, document.body);

Summary

Respond is a lightweight polyfill for min/max-width CSS3 Media Queries, while Preact is a modern JavaScript library for building user interfaces. Preact offers a more comprehensive solution for web development, with a focus on performance and compatibility with React. Respond, on the other hand, is specifically designed to address a particular browser compatibility issue. The code examples highlight the different purposes of these libraries, with Respond focusing on AJAX functionality and Preact demonstrating its React-like component structure.

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README

Respond.js

A fast & lightweight polyfill for min/max-width CSS3 Media Queries (for IE 6-8, and more)

  • Copyright 2011: Scott Jehl, scottjehl.com

  • Licensed under the MIT license.

The goal of this script is to provide a fast and lightweight (3kb minified / 1kb gzipped) script to enable responsive web designs in browsers that don't support CSS3 Media Queries - in particular, Internet Explorer 8 and under. It's written in such a way that it will probably patch support for other non-supporting browsers as well (more information on that soon).

If you're unfamiliar with the concepts surrounding Responsive Web Design, you can read up here and also here

Demo page (the colors change to show media queries working)

Usage Instructions

  1. Craft your CSS with min/max-width media queries to adapt your layout from mobile (first) all the way up to desktop
    @media screen and (min-width: 480px){
        /** ...styles for 480px and up go here **/
    }

  1. Reference the respond.min.js script (1kb min/gzipped) after all of your CSS (the earlier it runs, the greater chance IE users will not see a flash of un-media'd content)

  2. Crack open Internet Explorer and pump fists in delight

CDN/X-Domain Setup

Respond.js works by requesting a pristine copy of your CSS via AJAX, so if you host your stylesheets on a CDN (or a subdomain), you'll need to set up a local proxy to request the CSS for old IE browsers. Prior versions recommended a deprecated x-domain approach, but a local proxy is preferable (for performance and security reasons) to attempting to work around the cross-domain limitations.

Support & Caveats

Some notes to keep in mind:

  • This script's focus is purposely very narrow: only min-width and max-width media queries and all media types (screen, print, etc) are translated to non-supporting browsers. I wanted to keep things simple for filesize, maintenance, and performance, so I've intentionally limited support to queries that are essential to building a (mobile-first) responsive design. In the future, I may rework things a bit to include a hook for patching-in additional media query features - stay tuned!

  • Browsers that natively support CSS3 Media Queries are opted-out of running this script as quickly as possible. In testing for support, all other browsers are subjected to a quick test to determine whether they support media queries or not before proceeding to run the script. This test is now included separately at the top, and uses the window.matchMedia polyfill found here: https://github.com/paulirish/matchMedia.js . If you are already including this polyfill via Modernizr or otherwise, feel free to remove that part.

  • This script relies on no other scripts or frameworks (aside from the included matchMedia polyfill), and is optimized for mobile delivery (~1kb total filesize min/gzip)

  • As you might guess, this implementation is quite dumb in regards to CSS parsing rules. This is a good thing, because that allows it to run really fast, but its looseness may also cause unexpected behavior. For example: if you enclose a whole media query in a comment intending to disable its rules, you'll probably find that those rules will end up enabled in non-media-query-supporting browsers.

  • Respond.js doesn't parse CSS referenced via @import, nor does it work with media queries within style elements, as those styles can't be re-requested for parsing.

  • Due to security restrictions, some browsers may not allow this script to work on file:// urls (because it uses xmlHttpRequest). Run it on a web server.

  • If the request for the CSS file that includes MQ-specific styling is behind a redirect, Respond.js will fail silently. CSS files should respond with a 200 status.

  • Currently, media attributes on link elements are supported, but only if the linked stylesheet contains no media queries. If it does contain queries, the media attribute will be ignored and the internal queries will be parsed normally. In other words, @media statements in the CSS take priority.

  • Reportedly, if CSS files are encoded in UTF-8 with Byte-Order-Mark (BOM), they will not work with Respond.js in IE7 or IE8. Noted in issue #97

  • WARNING: Including @font-face rules inside a media query will cause IE7 and IE8 to hang during load. To work around this, place @font-face rules in the wide open, as a sibling to other media queries.

  • If you have more than 32 stylesheets referenced, IE will throw an error, Invalid procedure call or argument. Concatenate your CSS and the issue should go away.

  • Sass/SCSS source maps are not supported; @media -sass-debug-info will break respond.js. Noted in issue #148

  • Internet Explorer 9 supports css3 media queries, but not within frames when the CSS containing the media query is in an external file (this appears to be a bug in IE9 — see https://stackoverflow.com/questions/10316247/media-queries-fail-inside-ie9-iframe). See this commit for a fix if you're having this problem. https://github.com/NewSignature/Respond/commit/1c86c66075f0a2099451eb426702fc3540d2e603

  • Nested Media Queries are not supported

How's it work?

Basically, the script loops through the CSS referenced in the page and runs a regular expression or two on their contents to find media queries and their associated blocks of CSS. In Internet Explorer, the content of the stylesheet is impossible to retrieve in its pre-parsed state (which in IE 8-, means its media queries are removed from the text), so Respond.js re-requests the CSS files using Ajax and parses the text response from there. Be sure to configure your CSS files' caching properly so that this re-request doesn't actually go to the server, hitting your browser cache instead.

From there, each media query block is appended to the head in order via style elements, and those style elements are enabled and disabled (read: appended and removed from the DOM) depending on how their min/max width compares with the browser width. The media attribute on the style elements will match that of the query in the CSS, so it could be "screen", "projector", or whatever you want. Any relative paths contained in the CSS will be prefixed by their stylesheet's href, so image paths will direct to their proper destination

API Options?

Sure, a couple:

  • respond.update() : rerun the parser (helpful if you added a stylesheet to the page and it needs to be translated)
  • respond.mediaQueriesSupported: set to true if the browser natively supports media queries.
  • respond.getEmValue() : returns the pixel value of one em

Alternatives to this script

This isn't the only CSS3 Media Query polyfill script out there; but it damn well may be the fastest.

If you're looking for more robust CSS3 Media Query support, you might check out https://code.google.com/p/css3-mediaqueries-js/. In testing, I've found that script to be noticeably slow when rendering complex responsive designs (both in filesize and performance), but it really does support a lot more media query features than this script. Big hat tip to the authors! :)

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