autoprefixer

What is autoprefixer?

The autoprefixer npm package is a PostCSS plugin that parses your CSS and adds vendor prefixes to CSS rules using values from Can I Use. It is a tool that automates the process of adding vendor prefixes to CSS rules to ensure cross-browser compatibility.

What are autoprefixer's main functionalities?

Adding vendor prefixes

This feature automatically adds necessary vendor prefixes to CSS rules. The code sample shows how to use autoprefixer with PostCSS to process a CSS string that includes the 'display: flex;' rule, which then outputs the rule with the appropriate vendor prefixes.

const autoprefixer = require('autoprefixer');
const postcss = require('postcss');

postcss([ autoprefixer ]).process('a { display: flex; }').then(result => {
  console.log(result.css);
  // Output: 'a { display: -webkit-box; display: -ms-flexbox; display: flex; }'
});

Customizing browser support

Autoprefixer allows customization of the browsers you want to target. The code sample demonstrates how to specify the browsers using the 'overrideBrowserslist' option to target the last 2 versions of all browsers.

const autoprefixer = require('autoprefixer');
const postcss = require('postcss');

postcss([ autoprefixer({ overrideBrowserslist: ['last 2 versions'] }) ])
.process('a { display: flex; }').then(result => {
  console.log(result.css);
  // Output will include prefixes for the last 2 versions of all browsers.
});

Removing unnecessary prefixes

Autoprefixer can also remove outdated prefixes if they are no longer needed for the specified browser range. The code sample shows how to disable this feature using the 'remove' option.

const autoprefixer = require('autoprefixer');
const postcss = require('postcss');

postcss([ autoprefixer({ remove: false }) ])
.process('a { -webkit-box-shadow: 0 0 10px black; box-shadow: 0 0 10px black; }').then(result => {
  console.log(result.css);
  // Output will keep the -webkit-box-shadow prefix even if it's not necessary for the specified browsers.
});

Other packages similar to autoprefixer

postcss-preset-env

postcss-preset-env is a plugin that allows you to use future CSS features today. It includes autoprefixer functionality and extends it by allowing you to use future CSS syntax that is not yet fully supported in browsers.

cssnano

cssnano is a modular CSS minifier that includes autoprefixing as one of its optimizations. While autoprefixer focuses solely on adding prefixes, cssnano aims to reduce the size of CSS files by performing a variety of optimizations, including autoprefixing.

pleeease

pleeease is a CSS processor that combines several tools, including autoprefixer, to streamline the process of writing CSS. It simplifies the workflow by integrating autoprefixing, minification, and other features into one package.

README

Autoprefixer

Parse CSS and add vendor prefixes to CSS rules using values from Can I Use.

Write your CSS rules without vendor prefixes (in fact, forget about them entirely):

:fullscreen a {
    transition: transform 1s
}

Process your CSS by Autoprefixer:

var prefixed = autoprefixer.process(css).css;

It will use the data on current browser popularity and properties support to apply prefixes for you:

:-webkit-full-screen a {
    -webkit-transition: -webkit-transform 1s;
    transition: transform 1s
}
:-moz-full-screen a {
    transition: transform 1s
}
:-ms-fullscreen a {
    transition: transform 1s
}
:fullscreen a {
    -webkit-transition: -webkit-transform 1s;
    transition: transform 1s
}

You can play with your CSS in the interactive demo of Autoprefixer.

Twitter account for news and releases: @autoprefixer.

Sponsored by Evil Martians. Based on PostCSS framework.

Features

Forget about prefixes

The best tool is a tool you can't see and one that does the work for you. This is the main idea behind Autoprefixer.

Autoprefixer interface is simple: just forget about vendor prefixes and write normal CSS according to the latest W3C specs. You don’t need a special language (like Sass) or special mixins.

Because Autoprefixer is a postprocessor for CSS, you can also use it with preprocessors, such as Sass, Stylus or LESS.

Actual data from Can I Use

Autoprefixer uses the most recent data from Can I Use, understands which browsers are actual and popular and adds only the necessary vendor prefixes.

It also cleans your CSS from old prefixes (like prefixed border-radius, produced by many CSS libraries):

a {
    -webkit-border-radius: 5px;
    border-radius: 5px
}

compiles to:

a {
    border-radius: 5px
}

Note, that Autoprefixer doesn’t load Can I Use data every time. This data is already packed in the release, so the same Autoprefixer version will always have same output.

Flexbox, Gradients, etc.

Flexbox or gradients have different syntaxes in different browsers (sometimes you need to recalculate angles, sometimes you need 2 old properties instead of new one), but Autoprefixer hides this from you.

Just code by latest W3C specs and Autoprefixer will produce the code for old browsers:

a {
    display: flex;
}

compiles to:

a {
    display: -webkit-box;
    display: -webkit-flex;
    display: -moz-box;
    display: -ms-flexbox;
    display: flex
}

Autoprefixer has 22 special hacks to fix browser’s differences.

Fast

Autoprefixer is about several times faster than Compass and Stylus.

On a Core i7 with 10 GB of RAM and SSD, benchmark with GitHub styles is:

~/Dev/autoprefixer$ ./node_modules/.bin/cake bench
Load GitHub styles
Autoprefixer: 466 ms
Compass:      2828 ms (6.1 times slower)
Stylus:       1491 ms (3.2 times slower)

Unlike -prefix-free, Autoprefixer compiles CSS once on deploy and doesn’t hurt client-side performance.

Browsers

You can specify the browsers you want to target in your project:

autoprefixer("last 1 version", "> 1%", "Explorer 7").process(css).css;

• last 2 versions is last versions for each browser. Like “last 2 versions” strategy in Google.
• last 2 Chrome versions is last versions of the specified browser.
• > 5% is browser versions, selected by global usage statistics.
• Firefox > 20 is Firefox versions newer than 20.
• Firefox >= 20 is Firefox version 20 or newer.
• Firefox ESR is the latest Firefox ESR version.
• none don’t set any browsers to clean CSS from any vendor prefixes.
• ios 7 to set browser version directly.

Blackberry and stock Android browsers will not be used in last n versions. You can add them by name:

autoprefixer("last 1 version", "BlackBerry 10", "Android 4").process(css).css;

Browsers names (case insensitive):

• Android for old Android stock browser.
• BlackBerry or bb for Blackberry browser.
• Chrome for Google Chrome.
• Firefox or ff for Mozilla Firefox.
• Explorer or ie for Internet Explorer.
• iOS for iOS Safari.
• Opera for Opera.
• Safari for desktop Safari.

By default, Autoprefixer uses > 1%, last 2 versions, Firefox ESR, Opera 12.1:

• Latest Firefox ESR is a 24 version.
• Opera 12.1 will be in list until Opera supports non-Blink 12.x branch.

Source Map

You must set input and output CSS files paths (by from and to options) to generate a correct map.

Autoprefixer can modify previous source maps (for example, from Sass): it will autodetect a previous map if it is listed in an annotation comment or in a file near the input CSS. You can disable source map with map: false or set the previous source map content manually to map option (as a string or a JS object).

var result = autoprefixer.process(css, {
    map:   fs.readFileSync('main.sass.css.map'),
    from: 'main.sass.css',
    to:   'main.min.css'
});

result.css //=> CSS with source map annotation comment
result.map //=> Source map from main.sass to main.min.css

fs.writeFileSync('main.min.css.map', result.map);

Autoprefixer supports inline source maps too. If input CSS contains annotation from the previous step with map in data:uri, Autoprefixer will update the source map with prefixes changes and inine the new map back into the output CSS.

You can read more about source map options in PostCSS documentation.

Visual Cascade

Autoprefixer can change CSS indentation to create a nice visual cascade of prefixes. You need to send cascade: true option to processor constructor:

autoprefixer("> 1 %", "last 2 version", { cascade: true }).process(css).css

and, if CSS will be uncompressed, output would be like:

a {
    -webkit-box-sizing: border-box;
       -moz-box-sizing: border-box;
            box-sizing: border-box
}

Debug

You can check which browsers are selected and which properties will be prefixed:

info = autoprefixer("last 1 version").info();
console.log(info);

Or by CLI command:

autoprefixer -i

FAQ

Does it add polyfills for old browsers?

No. Autoprefixer only adds prefixes, not polyfills. There are two reasons:

1. Prefixes and polyfills are very different and need a different API. Two separate libraries would be much better.
2. Most of IE polyfills are very bad for client perfomance. They use slow hacks and old IEs is mostly used on old hardware. Most CSS3 features used only for styling should be ignored in old IEs as is recommended for Graceful Degradation.

Why don’t gradients work in Firefox?

Check that you use correct direction syntax. For example, you should use to bottom instead of top:

a {
  background: linear-gradient(to bottom, white, black)
}

Unfortunately, unprefixed gradients use a different direction syntax and most examples you find use an old gradient syntax, so be careful and use always the latest W3C specs with Autoprefixer.

Why doesn’t Autoprefixer add prefixes to border-radius?

Developers are often surprised by how few prefixes are required today. If Autoprefixer doesn’t add prefixes to your CSS, check if they’re still required on Can I Use.

If a prefix is required, but Autoprefixer doesn’t add it or adds it incorrectly, please report an issue and include your source CSS and expected output.

Why doesn’t Autoprefixer support appearance?

Unlike transition, the appearance property is not a part of any specification. So there is no appearance, only -moz-appearance and -webkit-appearance. Quote from MDN:

Do not use this property on Web sites: not only is it non-standard, but its behavior changes from one browser to another. Even the keyword none does not have the same behavior on each form element across different browsers, and some do not support it at all.

Why does Autoprefixer use CoffeeScript?

JavaScript is very popular, but this is the same reason why its syntax does not evolve. There is an entire Internet with a lot of legacy code which should be supported by browsers. If developers add an inappropriate feature then it can’t be removed in then next versions but must be supported for a very long time. This is very bad for innovation. To create new, we need to experiment and to choose.

As a result JavaScript doesn’t have even basic syntax features, which are present in other languages like Ruby or Python. There are no string interpolation, short lambda syntax, foreach statement for arrays, string and arrays slicing, etc. This features are really important and they will be in ECMAScript 6 (first update of JS syntax after 15 years), but this new specification is still not released and, of course, we must wait until all browsers support it.

With JavaScript preprocessors like CoffeeScript or TypeScript we can bring innovation back. We can add a new operator and use it right now, without waiting for support in all browsers.

Autoprefixer was written in pure JavaScript before. But CoffeeScript made Autoprefixer code much cleaner and more readable. Often, 2 lines of code became 1.

Don’t be afraid of CoffeeScript. It is just a new syntax, not another language (like ClojureScript). You can open examples on CoffeeScript.org and start to code. After a week your eyes will adjust and you will see that CoffeeScript is cleaner and more readable.

Situation with CoffeeScript and JavaScript is absolutely the same as with CSS preprocessors and postprocessors. How can we develop a CSS postprocessor and avoid using a JS preproccesor :).

Usage

Grunt

You can use the grunt-autoprefixer plugin for Grunt. Install the npm package and add it to Gruntfile:

grunt.loadNpmTasks('grunt-autoprefixer');

Gulp

You can use gulp-autoprefixer to use Autoprefixer in your Gulp build configuration.

var prefix = require('gulp-autoprefixer');
gulp.src('./css/*.css')
  .pipe(prefix(["last 1 version", "> 1%", "ie 8", "ie 7"], { cascade: true }))
  .pipe(gulp.dest('./dist/'));

Brunch

You can use the autoprefixer-brunch plugin for Brunch.

Compass

If you use Compass binary to compile your styles, you can easily integrate Autoprefixer with it. Install autoprefixer-rails gem:

gem install autoprefixer-rails

and add post-compile hook to config.rb:

require 'autoprefixer-rails'

on_stylesheet_saved do |file|
  css = File.read(file)
  File.open(file, 'w') do |io|
    io << AutoprefixerRails.process(css)
  end
end

You can set the browsers option as the second argument in process method:

io << AutoprefixerRails.process(css, browsers: ["last 1 version", "> 1%"])

Stylus

If you use Stylus CLI, you can add Autoprefixer by autoprefixer-stylus plugin.

Just install npm package and use it in -u option:

stylus -u autoprefixer-stylus -w file.styl

Ruby on Rails

Add autoprefixer-rails gem to Gemfile and write CSS in a usual way:

gem "autoprefixer-rails"

Ruby

You can integrate Autoprefixer into your Sprockets environment by autoprefixer-rails gem:

AutoprefixerRails.install(sprockets_env)

or process CSS from plain Ruby:

prefixed = AutoprefixerRails.process(css)

CodeKit

CodeKit, since the 2.0 version, contains Autoprefixer. In the After Compiling section, there is a checkbox to enable Autoprefixer. Read CodeKit docs for more inforamtion.

Prepros

If you want to build your assets with a GUI, try Prepros. Just set “Auto Prefix CSS” checkbox in right panel.

Broccoli

You can use the broccoli-autoprefixer plugin for Broccoli.

Mincer

To use Autoprefixer in Mincer, install autoprefixer npm package and enable it:

environment.enable('autoprefixer');

Middleman

Add middleman-autoprefixer gem to Gemfile:

gem "middleman-autoprefixer"

and activate the extension in your project’s config.rb:

activate :autoprefixer

Node.js

Use autoprefixer npm package:

var autoprefixer = require('autoprefixer');
var css          = 'a { transition: transform 1s }';
var prefixed     = autoprefixer.process(css).css;

PHP

You can use Autoprefixer in PHP by autoprefixer-php library:

$autoprefixer = new Autoprefixer();
$css          = 'a { transition: transform 1s }';
$prefixed     = $autoprefixer->compile($css);

.NET

You can use Autoprefixer from .NET and BundleTransformer with the Autoprefixer NuGet package.

JavaScript

You can use Autoprefixer in the browser or as a non-Node.js runtime with standalone version.

PostCSS

Autoprefixer can be also used as a PostCSS processor, so you can combine it with other processors and parse CSS only once:

postcss().
    use( autoprefixer(['> 1%', 'opera 12.5']).postcss ).
    use( compressor ).
    process(css);

Sublime Text

You can process your styles directly in Sublime Text with the sublime-autoprefixer plugin.

Brackets

Styles can processed automatically in Brackets using the brackets-autoprefixer extension.

Atom Editor

You can process your styles directly in Atom with the atom-autoprefixer package.

Others

You can use the autoprefixer binary to process CSS files using any assets manager:

sudo npm install --global autoprefixer
autoprefixer *.css

See autoprefixer -h for help.