@emotion/babel-plugin

Babel plugin for the minification and optimization of emotion styles.

@emotion/babel-plugin is highly recommended, but not required in version 8 and
above of Emotion.

Features

Example

In

 const myStyles = css`
  font-size: 20px;
  @media (min-width: 420px) {
    color: blue;
    ${css`
      width: 96px;
      height: 96px;
    `};
    line-height: 26px;
  }
  background: green;
  ${{ backgroundColor: 'hotpink' }};
`

Out

 const myStyles = /* #__PURE__ */ css(
  'font-size:20px;@media(min-width:420px){color:blue;',
  /* #__PURE__ */ css('width:96px;height:96px;'),
  ';line-height:26px;}background:green;',
  { backgroundColor: 'hotpink' },
  ';'
)

Installation

 yarn add --dev @emotion/babel-plugin

or if you prefer npm

 npm install --save-dev @emotion/babel-plugin

Usage

Via .babelrc (Recommended)

.babelrc

Without options:

 {
  "plugins": ["@emotion"]
}

With options:

Defaults Shown

 {
  "plugins": [
    [
      "@emotion",
      {
        // sourceMap is on by default but source maps are dead code eliminated in production
        "sourceMap": true,
        "autoLabel": "dev-only",
        "labelFormat": "[local]",
        "cssPropOptimization": true
      }
    ]
  ]
}

Recommended Setup

.babelrc

 {
  "plugins": ["@emotion"]
}

Via CLI

 babel --plugins @emotion/babel-plugin script.js

Via Node API

 require('@babel/core').transform('code', {
  plugins: ['@emotion/babel-plugin']
})

Options

sourceMap

boolean, defaults to true.

This option enables the following:

• Injected source maps for use in browser dev tools

Documentation

Note:

Source maps are on by default in @emotion/babel-plugin but they will be removed in production builds

autoLabel

'dev-only' | 'always' | 'never', defaults to dev-only.

This option enables the following:

• Automatically adds the label property to styles so that class names
  generated by css or styled include the name of the variable the result is
  assigned to.
• Please note that non word characters in the variable will be removed
  (Eg. iconStyles$1 will become iconStyles1) because $ is not valid
  CSS ClassName Selector

Each possible value for this option produces different output code:

• with dev-only we optimize the production code, so there are no labels added there, but at the same time we keep labels for development environments,
• with always we always add labels when possible,
• with never we disable this entirely and no labels are added.

css

In

 const brownStyles = css({ color: 'brown' })

Out

 const brownStyles = /*#__PURE__*/ css({ color: 'brown' }, 'label:brownStyles;')

brownStyles's value would be css-1q8eu9e-brownStyles

labelFormat

string, defaults to "[local]".

This option only works when autoLabel is set to 'dev-only' or 'always'. It allows you to
define the format of the resulting label. The format is defined via string where
variable parts are enclosed in square brackets [].
For example labelFormat: "my-classname--[local]", where [local] will be replaced
with the name of the variable the result is assigned to.

Allowed values:

• [local] - the name of the variable the result of the css or styled expression is assigned to.
• [filename] - name of the file (without extension) where css or styled expression is located.
• [dirname] - name of the directory containing the file where css or styled expression is located.

This format only affects the label property of the expression, meaning that the css prefix and hash will
be prepended automatically.

css

In

 // BrownView.js
// autoLabel: 'dev-only'
// labelFormat: '[filename]--[local]'
const brownStyles = css({ color: 'brown' })

Out

 const brownStyles = /*#__PURE__*/ css(
  { color: 'brown' },
  'label:BrownView--brownStyles;'
)

BrownView--brownStyles's value would be css-hash-BrownView--brownStyles

styled

In

 const H1 = styled.h1({
  borderRadius: '50%',
  transition: 'transform 400ms ease-in-out',
  boxSizing: 'border-box',
  display: 'flex',
  ':hover': {
    transform: 'scale(1.2)'
  }
})

Out

 const H1 = /*#__PURE__*/ styled('h1', {
  label: 'H1'
})({
  borderRadius: '50%',
  transition: 'transform 400ms ease-in-out',
  boxSizing: 'border-box',
  display: 'flex',
  ':hover': {
    transform: 'scale(1.2)'
  }
})

H1's class name attribute would be css-hash-H1

cssPropOptimization

boolean, defaults to true.

This option assumes that you are using something to make @emotion/react's jsx function work for all jsx. If you are not doing so and you do not want such optimizations to occur, disable this option.

importMap

This option allows you to tell @emotion/babel-plugin what imports it should look at to determine what it should transform so if you re-export Emotion's exports, you can still use the Babel transforms

An example file:

 import { anotherExport } from 'my-package';
import { someExport, thisIsTheJsxExport } from 'some-package';

An example config:

 {
  "my-package": {
    "anotherExport": {
      "canonicalImport": ["@emotion/styled", "default"],
      "styledBaseImport": ["my-package/base", "anotherExport"]
    }
  },
  "some-package": {
    "someExport": {
      "canonicalImport": ["@emotion/react", "css"]
    },
    "thisIsTheJsxExport": {
      "canonicalImport": ["@emotion/react", "jsx"]
    }
  }
}

Babel Macros

Instead of using @emotion/babel-plugin, you can use emotion with babel-plugin-macros. Add babel-plugin-macros to your babel config (which is included in Create React App 2.0) and use the imports/packages shown below.

 import {
  css,
  keyframes,
  injectGlobal,
  flush,
  hydrate
} from '@emotion/css/macro'
import { jsx, css, Global, keyframes } from '@emotion/react/macro'
import styled from '@emotion/styled/macro'