babel-plugin-emotion

What is babel-plugin-emotion?

The babel-plugin-emotion npm package is designed to enhance the development experience when using Emotion, a popular CSS-in-JS library. It provides optimizations and custom transformations for styles defined in JavaScript, enabling more efficient and powerful styling solutions in React applications. This plugin facilitates the use of Emotion by offering features such as source maps for easier debugging, auto-labeling for better readability of class names, and the optimization of styles for production.

What are babel-plugin-emotion's main functionalities?

Source Maps

Generates source maps for styles, improving the debugging process by allowing developers to trace back to the original location of a style definition within their code.

"use strict";

var _emotion = require("@emotion/core");

function App() {
  return /*#__PURE__*/_emotion.jsx("div", {
    css: {
      color: 'hotpink'
    }
  }, "Hello World");
}

Auto-labeling

Automatically adds labels to the generated class names based on the name of the variable or component. This enhances readability in the DOM and helps in identifying components during debugging.

"use strict";

var _emotion = require("@emotion/core");

var _styled = /*#__PURE__*/(0, _emotion.default)("div")
/*#__PURE__*/
.emotionLabel('MyComponent_styled_h1nx9f');

Optimization for Production

In production, the plugin optimizes the styles by compacting and efficient handling, reducing the size of the generated CSS and improving load times.

process.env.NODE_ENV === 'production' ? /*#__PURE__*/require('@emotion/css').css('label:MyComponent;', 'color:hotpink;') : /*#__PURE__*/require('@emotion/css').css('color:hotpink;');

Other packages similar to babel-plugin-emotion

styled-components

Styled-components is another CSS-in-JS library that allows for styling applications using tagged template literals. While it offers similar functionality in terms of defining styles within JavaScript, it differs in syntax and the way styles are applied. Styled-components focuses on creating styled components without the need for a separate CSS file, whereas babel-plugin-emotion enhances the Emotion library's capabilities with additional compile-time optimizations and features.

babel-plugin-styled-components

This plugin is specifically designed for styled-components, offering similar compile-time enhancements as babel-plugin-emotion but for styled-components. It includes features like server-side rendering optimizations, better debugging with readable class names, and minification of styles for production. The comparison lies in the focus of each plugin on its respective CSS-in-JS library, providing tailored optimizations and developer experience improvements.

README

babel-plugin-emotion

Babel plugin for the minification and optimization of emotion styles.

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

Features

Feature/Syntax	Native	Babel Plugin Required	Notes
css``	✅
css(...)	✅		Generally used for object styles.
components as selectors		✅	Allows an emotion component to be used as a CSS selector.
Minification		✅	Any leading/trailing space between properties in your css and styled blocks is removed. This can reduce the size of your final bundle.
Dead Code Elimination		✅	Uglifyjs will use the injected /*#__PURE__*/ flag comments to mark your css and styled blocks as candidates for dead code elimination.
Source Maps		✅	When enabled, navigate directly to the style declaration in your javascript file.
Contextual Class Names		✅	Generated class names include the name of the variable or component they were defined in.

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 babel-plugin-emotion

or if you prefer npm

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

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": process.env.NODE_ENV !== 'production',
        "labelFormat": "[local]",
        "cssPropOptimization": true
      }
    ]
  ]
}

Recommended Setup

.babelrc

{
  "plugins": ["emotion"]
}

Via CLI

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

Via Node API

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

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 babel-plugin-emotion but they will be removed in production builds

autoLabel

boolean, defaults to process.env.NODE_ENV !== 'production'.

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

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 true. 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: true
// 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

instances

Array<string>, defaults to

;['emotion']

This option allows babel-plugin-emotion to know which imports to treat as emotion imports and transform as such. This option is only required if you use a custom instance of emotion created with create-emotion or you're importing emotion from somewhere other than the paths above. Relative paths are resolved relative to process.cwd()(the current working directory).

Documentation

cssPropOptimization

boolean, defaults to true.

This option assumes that you are using something to make @emotion/core'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.

Babel Macros

Instead of using babel-plugin-emotion, 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 styled from 'react-emotion/macro'
import { css, keyframes, injectGlobal, flush, hydrate } from 'emotion/macro'
import css from '@emotion/css/macro'
import styled from '@emotion/styled/macro'