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Parse CSS and add vendor prefixes to rules by Can I Use

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Autoprefixer Cult Of Martians

PostCSS plugin to parse CSS and add vendor prefixes to CSS rules using values from Can I Use. It is recommended by Google and used in Twitter and Alibaba.

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

::placeholder {
  color: gray;
}

.image {
  background-image: url(image@1x.png);
}
@media (min-resolution: 2dppx) {
  .image {
    background-image: url(image@2x.png);
  }
}

Autoprefixer will use the data based on current browser popularity and property support to apply prefixes for you. You can try the interactive demo of Autoprefixer.

::-webkit-input-placeholder {
  color: gray;
}
::-moz-placeholder {
  color: gray;
}
:-ms-input-placeholder {
  color: gray;
}
::-ms-input-placeholder {
  color: gray;
}
::placeholder {
  color: gray;
}

.image {
  background-image: url(image@1x.png);
}
@media (-webkit-min-device-pixel-ratio: 2),
       (-o-min-device-pixel-ratio: 2/1),
       (min-resolution: 2dppx) {
  .image {
    background-image: url(image@2x.png);
  }
}

Twitter account for news and releases: @autoprefixer.

Sponsored by Evil Martians

Contents

Browsers

Autoprefixer uses Browserslist, so you can specify the browsers you want to target in your project with queries like > 5% (see Best Practices).

The best way to provide browsers is a .browserslistrc file in your project root, or by adding a browserslist key to your package.json.

We recommend the use of these options over passing options to Autoprefixer so that the config can be shared with other tools such as babel-preset-env and Stylelint.

See Browserslist docs for queries, browser names, config format, and defaults.

FAQ

Does Autoprefixer polyfill Grid Layout for IE?

Autoprefixer can be used to translate modern CSS Grid syntax into IE 10 and IE 11 syntax, but this polyfill will not work in 100% of cases. This is why it is disabled by default.

First, you need to enable Grid prefixes by using either the grid: "autoplace" option or the /* autoprefixer grid: autoplace */ control comment. Also you can use environment variable to enable Grid: AUTOPREFIXER_GRID=autoplace npm build.

Second, you need to test every fix with Grid in IE. It is not an enable and forget feature, but it is still very useful. Financial Times and Yandex use it in production.

Third, there is only very limited auto placement support. Read the Grid Autoplacement support in IE section for more details.

Fourth, if you are not using the autoplacement feature, the best way to use Autoprefixer is by using grid-template or grid-template-areas.

.page {
  display: grid;
  grid-gap: 33px;
  grid-template:
    "head head  head" 1fr
    "nav  main  main" minmax(100px, 1fr)
    "nav  foot  foot" 2fr /
    1fr   100px 1fr;
}
.page__head {
  grid-area: head;
}
.page__nav {
  grid-area: nav;
}
.page__main {
  grid-area: main;
}
.page__footer {
  grid-area: foot;
}

See also:

Does it add polyfills?

No. Autoprefixer only adds prefixes.

Most new CSS features will require client side JavaScript to handle a new behavior correctly.

Depending on what you consider to be a “polyfill”, you can take a look at some other tools and libraries. If you are just looking for syntax sugar, you might take a look at:

  • postcss-preset-env is a plugins preset with polyfills and Autoprefixer to write future CSS today.
  • Oldie, a PostCSS plugin that handles some IE hacks (opacity, rgba, etc).
  • postcss-flexbugs-fixes, a PostCSS plugin to fix flexbox issues.

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.

Why does Autoprefixer use unprefixed properties in @-webkit-keyframes?

Browser teams can remove some prefixes before others, so we try to use all combinations of prefixed/unprefixed values.

How to work with legacy -webkit- only code?

Autoprefixer needs unprefixed property to add prefixes. So if you only wrote -webkit-gradient without W3C’s gradient, Autoprefixer will not add other prefixes.

But PostCSS has plugins to convert CSS to unprefixed state. Use postcss-unprefix before Autoprefixer.

Does Autoprefixer add -epub- prefix?

No, Autoprefixer works only with browsers prefixes from Can I Use. But you can use postcss-epub for prefixing ePub3 properties.

Why doesn’t Autoprefixer transform generic font-family system-ui?

system-ui is technically not a prefix and the transformation is not future-proof. You can use postcss-font-family-system-ui to transform system-ui to a practical font-family list.

Usage

Gulp

In Gulp you can use gulp-postcss with autoprefixer npm package.

gulp.task('autoprefixer', () => {
  const autoprefixer = require('autoprefixer')
  const sourcemaps = require('gulp-sourcemaps')
  const postcss = require('gulp-postcss')

  return gulp.src('./src/*.css')
    .pipe(sourcemaps.init())
    .pipe(postcss([ autoprefixer() ]))
    .pipe(sourcemaps.write('.'))
    .pipe(gulp.dest('./dest'))
})

With gulp-postcss you also can combine Autoprefixer with other PostCSS plugins.

Webpack

In webpack you can use postcss-loader with autoprefixer and other PostCSS plugins.

module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/,
        use: ["style-loader", "css-loader", "postcss-loader"]
      }
    ]
  }
}

And create a postcss.config.js with:

module.exports = {
  plugins: [
    require('autoprefixer')
  ]
}

CSS-in-JS

The best way to use PostCSS with CSS-in-JS is astroturf. Add its loader to your webpack.config.js:

module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/,
        use: ['style-loader', 'postcss-loader'],
      },
      {
        test: /\.jsx?$/,
        use: ['babel-loader', 'astroturf/loader'],
      }
    ]
  }
}

Then create postcss.config.js:

module.exports = {
  plugins: [
    require('autoprefixer')
  ]
}

CLI

You can use the postcss-cli to run Autoprefixer from CLI:

npm install postcss-cli autoprefixer
npx postcss *.css --use autoprefixer -d build/

See postcss -h for help.

Other Build Tools

Preprocessors

GUI Tools

JavaScript

You can use Autoprefixer with PostCSS in your Node.js application or if you want to develop an Autoprefixer plugin for a new environment.

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

postcss([ autoprefixer ]).process(css).then(result => {
  result.warnings().forEach(warn => {
    console.warn(warn.toString())
  })
  console.log(result.css)
})

There is also a standalone build for the browser or for a non-Node.js runtime.

You can use html-autoprefixer to process HTML with inlined CSS.

Text Editors and IDE

Autoprefixer should be used in assets build tools. Text editor plugins are not a good solution, because prefixes decrease code readability and you will need to change values in all prefixed properties.

I recommend you to learn how to use build tools like Parcel. They work much better and will open you a whole new world of useful plugins and automation.

If you can’t move to a build tool, you can use text editor plugins:

Warnings

Autoprefixer uses the PostCSS warning API to warn about really important problems in your CSS:

  • Old direction syntax in gradients.
  • Old unprefixed display: box instead of display: flex by latest specification version.

You can get warnings from result.warnings():

result.warnings().forEach(warn => {
  console.warn(warn.toString())
})

Every Autoprefixer runner should display these warnings.

Disabling

Prefixes

Autoprefixer was designed to have no interface – it just works. If you need some browser specific hack just write a prefixed property after the unprefixed one.

a {
  transform: scale(0.5);
  -moz-transform: scale(0.6);
}

If some prefixes were generated incorrectly, please create an issue on GitHub.

Features

You can use these plugin options to control some of Autoprefixer’s features.

  • grid: "autoplace" will enable -ms- prefixes for Grid Layout including some limited autoplacement support.
  • supports: false will disable @supports parameters prefixing.
  • flexbox: false will disable flexbox properties prefixing. Or flexbox: "no-2009" will add prefixes only for final and IE versions of specification.
  • remove: false will disable cleaning outdated prefixes.

You should set them inside the plugin like so:

autoprefixer({ grid: 'autoplace' })

Control Comments

If you do not need Autoprefixer in some part of your CSS, you can use control comments to disable Autoprefixer.

.a {
  transition: 1s; /* will be prefixed */
}

.b {
  /* autoprefixer: off */
  transition: 1s; /* will not be prefixed */
}

.c {
  /* autoprefixer: ignore next */
  transition: 1s; /* will not be prefixed */
  mask: url(image.png); /* will be prefixed */
}

There are three types of control comments:

  • /* autoprefixer: (on|off) */: enable/disable all Autoprefixer translations for the whole block both before and after the comment.
  • /* autoprefixer: ignore next */: disable Autoprefixer only for the next property or next rule selector or at-rule parameters (but not rule/at‑rule body).
  • /* autoprefixer grid: (autoplace|no-autoplace|off) */: control how Autoprefixer handles grid translations for the whole block:
    • autoplace: enable grid translations with autoplacement support.
    • no-autoplace: enable grid translations with autoplacement support disabled (alias for deprecated value on).
    • off: disable all grid translations.

You can also use comments recursively:

/* autoprefixer: off */
@supports (transition: all) {
  /* autoprefixer: on */
  a {
    /* autoprefixer: off */
  }
}

Note that comments that disable the whole block should not be featured in the same block twice:

/* How not to use block level control comments */

.do-not-do-this {
  /* autoprefixer: off */
  transition: 1s;
  /* autoprefixer: on */
  transform: rotate(20deg);
}

Options

Function autoprefixer(options) returns a new PostCSS plugin. See PostCSS API for plugin usage documentation.

autoprefixer({ cascade: false })

Available options are:

  • env (string): environment for Browserslist.
  • cascade (boolean): should Autoprefixer use Visual Cascade, if CSS is uncompressed. Default: true
  • add (boolean): should Autoprefixer add prefixes. Default is true.
  • remove (boolean): should Autoprefixer [remove outdated] prefixes. Default is true.
  • supports (boolean): should Autoprefixer add prefixes for @supports parameters. Default is true.
  • flexbox (boolean|string): should Autoprefixer add prefixes for flexbox properties. With "no-2009" value Autoprefixer will add prefixes only for final and IE 10 versions of specification. Default is true.
  • grid (false|"autoplace"|"no-autoplace"): should Autoprefixer add IE 10-11 prefixes for Grid Layout properties?
    • false (default): prevent Autoprefixer from outputting CSS Grid translations.
    • "autoplace": enable Autoprefixer grid translations and include autoplacement support. You can also use /* autoprefixer grid: autoplace */ in your CSS.
    • "no-autoplace": enable Autoprefixer grid translations but exclude autoplacement support. You can also use /* autoprefixer grid: no-autoplace */ in your CSS. (alias for the deprecated true value)
  • stats (object): custom usage statistics for > 10% in my stats browsers query.
  • overrideBrowserslist (array): list of queries for target browsers. Try to not use it. The best practice is to use .browserslistrc config or browserslist key in package.json to share target browsers with Babel, ESLint and Stylelint. See Browserslist docs for available queries and default value.
  • ignoreUnknownVersions (boolean): do not raise error on unknown browser version in Browserslist config. Default is false.

Plugin object has info() method for debugging purpose.

You can use PostCSS processor to process several CSS files to increase performance.

Environment Variables

  • AUTOPREFIXER_GRID: (autoplace|no-autoplace) should Autoprefixer add IE 10-11 prefixes for Grid Layout properties?
    • autoplace: enable Autoprefixer grid translations and include autoplacement support.
    • no-autoplace: enable Autoprefixer grid translations but exclude autoplacement support.

Environment variables are useful, when you want to change Autoprefixer options but don't have access to config files. Create React App is a good example of this.

Using environment variables to support CSS Grid prefixes in Create React App

  1. Install the latest version of Autoprefixer and cross-env:
npm install autoprefixer@latest cross-env --save-dev
  1. Under "browserslist" > "development" in the package.json file, add "last 1 ie version"
"browserslist": {
  "production": [
    ">0.2%",
    "not dead",
    "not op_mini all"
  ],
  "development": [
    "last 1 chrome version",
    "last 1 firefox version",
    "last 1 safari version",
    "last 1 ie version"
  ]
}
  1. Update "scripts" in the package.json file to the following:
"scripts": {
  "start": "cross-env AUTOPREFIXER_GRID=autoplace react-scripts start",
  "build": "cross-env AUTOPREFIXER_GRID=autoplace react-scripts build",
  "test": "cross-env AUTOPREFIXER_GRID=autoplace react-scripts test",
  "eject": "react-scripts eject"
},

Replace autoplace with no-autoplace in the above example if you prefer to disable Autoprefixer Grid autoplacement support.

Now when you run npm start you will see CSS Grid prefixes automatically being applied to your output CSS.

See also Browserslist environment variables for more examples on how to use environment variables in your project.

Grid Autoplacement support in IE

If the grid option is set to "autoplace", limited autoplacement support is added to Autoprefixers grid translations. You can also use the /* autoprefixer grid: autoplace */ control comment or AUTOPREFIXER_GRID=autoplace npm build environment variable.

Autoprefixer will only autoplace grid cells if both grid-template-rows and grid-template-columns has been set. If grid-template or grid-template-areas has been set, Autoprefixer will use area based cell placement instead.

Autoprefixer supports autoplacement by using nth-child CSS selectors. It creates [number of columns] x [number of rows] nth-child selectors. For this reason Autoplacement is only supported within the explicit grid.

/* Input CSS */

/* autoprefixer grid: autoplace */

.autoplacement-example {
  display: grid;
  grid-template-columns: 1fr 1fr;
  grid-template-rows: auto auto;
  grid-gap: 20px;
}
/* Output CSS */

/* autoprefixer grid: autoplace */

.autoplacement-example {
  display: -ms-grid;
  display: grid;
  -ms-grid-columns: 1fr 20px 1fr;
  grid-template-columns: 1fr 1fr;
  -ms-grid-rows: auto 20px auto;
  grid-template-rows: auto auto;
  grid-gap: 20px;
}

.autoplacement-example > *:nth-child(1) {
  -ms-grid-row: 1;
  -ms-grid-column: 1;
}

.autoplacement-example > *:nth-child(2) {
  -ms-grid-row: 1;
  -ms-grid-column: 3;
}

.autoplacement-example > *:nth-child(3) {
  -ms-grid-row: 3;
  -ms-grid-column: 1;
}

.autoplacement-example > *:nth-child(4) {
  -ms-grid-row: 3;
  -ms-grid-column: 3;
}

Beware of enabling autoplacement in old projects

Be careful about enabling autoplacement in any already established projects that have previously not used Autoprefixer's grid autoplacement feature before.

If this was your html:

<div class="grid">
  <div class="grid-cell"></div>
</div>

The following CSS will not work as expected with the autoplacement feature enabled:

/* Unsafe CSS when Autoplacement is enabled */

.grid-cell {
  grid-column: 2;
  grid-row: 2;
}

.grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  grid-template-rows: repeat(3, 1fr);
}

Swapping the rules around will not fix the issue either:

/* Also unsafe to use this CSS */

.grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  grid-template-rows: repeat(3, 1fr);
}

.grid-cell {
  grid-column: 2;
  grid-row: 2;
}

One way to deal with this issue is to disable autoplacement in the grid-declaration rule:

/* Disable autoplacement to fix the issue */

.grid {
  /* autoprefixer grid: no-autoplace */
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  grid-template-rows: repeat(3, 1fr);
}

.grid-cell {
  grid-column: 2;
  grid-row: 2;
}

The absolute best way to integrate autoplacement into already existing projects though is to leave autoplacement turned off by default and then use a control comment to enable it when needed. This method is far less likely to cause something on the site to break.

/* Disable autoplacement by default in old projects */
/* autoprefixer grid: no-autoplace */

/* Old code will function the same way it always has */
.old-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  grid-template-rows: repeat(3, 1fr);
}
.old-grid-cell {
  grid-column: 2;
  grid-row: 2;
}

/* Enable autoplacement when you want to use it in new code */
.new-autoplace-friendly-grid {
  /* autoprefixer grid: autoplace */
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  grid-template-rows: repeat(3, auto);
}

Note that the grid: "no-autoplace" setting and the /* autoprefixer grid: no-autoplace */ control comment share identical functionality to the grid: true setting and the /* autoprefixer grid: on */ control comment. There is no need to refactor old code to use no-autoplace in place of the old true and on statements.

Autoplacement limitations

Both columns and rows must be defined

Autoplacement only works inside the explicit grid. The columns and rows need to be defined so that Autoprefixer knows how many nth-child selectors to generate.

.not-allowed {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
}

.is-allowed {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  grid-template-rows: repeat(10, auto);
}

Repeat auto-fit and auto-fill are not supported

The repeat(auto-fit, ...) and repeat(auto-fill, ...) grid functionality relies on knowledge from the browser about screen dimensions and the number of available grid items for it to work properly. Autoprefixer does not have access to this information so unfortunately this little snippet will never be IE friendly.

.grid {
  /* This will never be IE friendly */
  grid-template-columns: repeat(auto-fit, min-max(200px, 1fr))
}

No manual cell placement or column/row spans allowed inside an autoplacement grid

Elements must not be manually placed or given column/row spans inside an autoplacement grid. Only the most basic of autoplacement grids are supported. Grid cells can still be placed manually outside the the explicit grid though. Support for manually placing individual grid cells inside an explicit autoplacement grid is planned for a future release.

.autoplacement-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  grid-template-rows: repeat(3, auto);
}

/* Grid cells placed inside the explicit grid
   will break the layout in IE */
.not-permitted-grid-cell {
  grid-column: 1;
  grid-row: 1;
}

/* Grid cells placed outside the
   explicit grid will work in IE */
.permitted-grid-cell {
  grid-column: 1 / span 2;
  grid-row: 4;
}

If manual cell placement is required, we recommend using grid-template or grid-template-areas instead:

.page {
  display: grid;
  grid-gap: 30px;
  grid-template:
      "head head"
      "nav  main" minmax(100px, 1fr)
      "foot foot" /
      200px 1fr;
}
.page__head {
  grid-area: head;
}
.page__nav {
  grid-area: nav;
}
.page__main {
  grid-area: main;
}
.page__footer {
  grid-area: foot;
}

Do not create ::before and ::after pseudo elements

Let's say you have this HTML:

<div class="grid">
  <div class="grid-cell"></div>
</div>

And you write this CSS:

.grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  grid-template-rows: auto;
}

.grid::before {
  content: 'before';
}

.grid::after {
  content: 'after';
}

This will be the output:

.grid {
  display: -ms-grid;
  display: grid;
  -ms-grid-columns: 1fr 1fr;
  grid-template-columns: 1fr 1fr;
  -ms-grid-rows: auto;
  grid-template-rows: auto;
}

.grid > *:nth-child(1) {
  -ms-grid-row: 1;
  -ms-grid-column: 1;
}


.grid > *:nth-child(2) {
  -ms-grid-row: 1;
  -ms-grid-column: 2;
}

.grid::before {
  content: 'before';
}

.grid::after {
  content: 'after';
}

IE will place .grid-cell, ::before and ::after in row 1 column 1. Modern browsers on the other hand will place ::before in row 1 column 1, .grid-cell in row 1 column 2, and ::after in row 2 column 1.

See this Code Pen to see a visualization of the issue. View the Code Pen in both a modern browser and IE to see the difference.

Note that you can still create ::before and ::after elements as long as you manually place them outside the explicit grid.

When changing the grid gap value, columns and rows must be re-declared

If you wish to change the size of a grid-gap, you will need to redeclare the grid columns and rows.

.grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  grid-template-rows: auto;
  grid-gap: 50px;
}

/* This will *NOT* work in IE */
@media (max-width: 600px) {
  .grid {
    grid-gap: 20px;
  }
}

/* This will *NOT* work in IE */
.grid.small-gap {
  grid-gap: 20px;
}
.grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  grid-template-rows: auto;
  grid-gap: 50px;
}

/* This *WILL* work in IE */
@media (max-width: 600px) {
  .grid {
    grid-template-columns: 1fr 1fr;
    grid-template-rows: auto;
    grid-gap: 20px;
  }
}

/* This *WILL* work in IE */
.grid.small-gap {
  grid-template-columns: 1fr 1fr;
  grid-template-rows: auto;
  grid-gap: 20px;
}

Debug

Run npx autoprefixer --info in your project directory to check which browsers are selected and which properties will be prefixed:

$ npx autoprefixer --info
Browsers:
  Edge: 16

These browsers account for 0.26% of all users globally

At-Rules:
  @viewport: ms

Selectors:
  ::placeholder: ms

Properties:
  appearance: webkit
  flow-from: ms
  flow-into: ms
  hyphens: ms
  overscroll-behavior: ms
  region-fragment: ms
  scroll-snap-coordinate: ms
  scroll-snap-destination: ms
  scroll-snap-points-x: ms
  scroll-snap-points-y: ms
  scroll-snap-type: ms
  text-size-adjust: ms
  text-spacing: ms
  user-select: ms

JS API is also available:

console.log(autoprefixer().info())

Security Contact

To report a security vulnerability, please use the Tidelift security contact. Tidelift will coordinate the fix and disclosure.

About

Parse CSS and add vendor prefixes to rules by Can I Use

twitter.com/autoprefixer

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