autoprefixer README

The project's README from github.com/postcss/autoprefixer. As one markdown file: README.md.

Autoprefixer

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 {
  width: stretch;
}

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.

::-moz-placeholder {
  color: gray;
}
::placeholder {
  color: gray;
}

.image {
  width: -moz-available;
  width: -webkit-fill-available;
  width: stretch;
}

Twitter account for news and releases: @autoprefixer.

  Autoprefixer is built by Evil Martians, an American design and engineering consultancy for developer tools, AI, and cybersecurity startups.

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:

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 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:

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.

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:

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:

Plugin object has info() method for debugging purpose.

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

Environment Variables

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 CodePen to see a visualization of the issue. View the CodePen 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.

For Enterprise

Available as part of the Tidelift Subscription.

The maintainers of autoprefixer and thousands of other packages are working with Tidelift to deliver commercial support and maintenance for the open source dependencies you use to build your applications. Save time, reduce risk, and improve code health, while paying the maintainers of the exact dependencies you use. Learn more.

autoprefixer (postcss/autoprefixer)

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22.2K ·GitHub
Autoprefixer
这是干什么的？一个 PostCSS 插件，会解析你的 CSS，并根据 Can I Use 的数据自动加上浏览器厂商前缀：你写规则时不用带前缀，它只会补充浏览器现在仍然需要的那几个。谷歌推荐使用，Twitter 和阿里巴巴也在用。
它是一个我要运行的软件，还是接入构建流程的一个库？它是一个 PostCSS 插件——一个在你的 CSS 构建环节里运行的 npm 包，不是一个独立的软件。它的设计就是没有界面：接入之后自动生效，不需要你操心。
怎么把它加到项目里？安装 autoprefixer npm 包，然后接入你的构建：Gulp 用 gulp-postcss，Webpack 用 postcss-loader 配合一个 postcss.config.js，或者直接在终端里用 postcss-cli。另外还有适配 Grunt、Rails、Jekyll、Less 和 Stylus 的插件。
它怎么知道要为哪些浏览器加前缀？它使用 Browserslist：你可以在 .browserslistrc 文件里，或者在 package.json 里加一个 browserslist 字段，用类似 > 5% 这样的查询来描述目标浏览器，这样同一份配置还能和 babel-preset-env、Stylelint 等工具共用。
它能帮我的浏览器补齐缺失的 CSS 功能吗？不能——它只加前缀，不做 polyfill：新的 CSS 行为仍然需要浏览器端的 JavaScript 来实现。如果想要“未来 CSS”的语法糖，README 推荐使用 postcss-preset-env。
我能在 Node.js 构建之外使用它吗？你的构建能在哪里跑，它就能在哪里跑——任何装有 Node.js 10、12 或 14+ 的操作系统都行。它还提供面向浏览器或非 Node 运行环境的独立版本，VS Code 和 Sublime 也有编辑器插件，不过 README 更推荐使用构建工具。
它能让现代的 CSS Grid 在 Internet Explorer 里正常工作吗？只能部分支持。它可以把现代 Grid 语法转换成 IE 10/11 能用的写法，但这个转换并不是 100% 的情况都能奏效，所以默认是关闭的——你需要用 grid: 'autoplace' 选项或 grid 控制注释来开启，每一处修复都要自己测试，而且自动布局（auto-placement）只支持很有限的一部分。
如果它加了一个我不想要的前缀怎么办？你可以在未加前缀的属性后面手动写出带前缀的版本，或者用 '/* autoprefixer: off */'、'/* autoprefixer: ignore next */' 这样的控制注释把 Autoprefixer 关掉。flexbox: false 或 remove: false 之类的选项可以关掉整个功能。
为什么它不给 border-radius 加前缀？因为如今需要前缀的场合已经很少了。如果 Autoprefixer 对你的 CSS 什么都没加，可以去 Can I Use 上查一下这些前缀是否还有存在的必要。
接入构建之前，我能先试试它的效果吗？可以——README 里链接了一个在线交互式演示，你把 CSS 粘贴进去，就能看到它会加哪些前缀。
What are similar projects?postcss, linaria, browserslist, vue-cli, angular-cli, razzle, vanilla-extract, vite
Which topics is it in?webpack, build-tool, css, plugin, web-development, npm, frontend, nodejs, library, javascript, cli, developer-tools
Creator
postcss
Size
8.2 MB
Stars
22.2K
Updated
CommitOct 07Release10.6.1Sep 15
Age
13y
Commits · 90 Days