# @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
<table>
<thead>
<tr>
<th>Feature/Syntax</th>
<th>Native</th>
<th>Babel Plugin Required</th>
<th>Notes</th>
</tr>
</thead>
<tbody>
<tr>
<td><code>css``</code></td>
<td align="center">✅</td>
<td align="center"></td>
<td></td>
</tr>
<tr>
<td><code>css(...)</code></td>
<td align="center">✅</td>
<td align="center"></td>
<td>Generally used for object styles.</td>
</tr>
<tr>
<td>components as selectors</td>
<td align="center"></td>
<td align="center">✅</td>
<td>Allows an emotion component to be <a href="https://emotion.sh/docs/styled#targeting-another-emotion-component">used as a CSS selector</a>.</td>
</tr>
<tr>
<td>Minification</td>
<td align="center"></td>
<td align="center">✅</td>
<td>Any leading/trailing space between properties in your <code>css</code> and <code>styled</code> blocks is removed. This can reduce the size of your final bundle.</td>
</tr>
<tr>
<td>Dead Code Elimination</td>
<td align="center"></td>
<td align="center">✅</td>
<td>Uglifyjs will use the injected <code>/*#__PURE__*/</code> flag comments to mark your <code>css</code> and <code>styled</code> blocks as candidates for dead code elimination.</td>
</tr>
<tr>
<td>Source Maps</td>
<td align="center"></td>
<td align="center">✅</td>
<td>When enabled, navigate directly to the style declaration in your javascript file.</td>
</tr>
<tr>
<td>Contextual Class Names</td>
<td align="center"></td>
<td align="center">✅</td>
<td>Generated class names include the name of the variable or component they were defined in.</td>
</tr>
</tbody>
</table>
## Example
**In**
```javascript
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**
```javascript
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
```bash
yarn add --dev @emotion/babel-plugin
```
or if you prefer npm
```bash
npm install --save-dev @emotion/babel-plugin
```
## Usage
### Via `.babelrc` (Recommended)
**.babelrc**
Without options:
```json
{
"plugins": ["@emotion"]
}
```
With options:
_Defaults Shown_
```js
{
"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**
```json
{
"plugins": ["@emotion"]
}
```
### Via CLI
```bash
babel --plugins @emotion/babel-plugin script.js
```
### Via Node API
```javascript
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**](https://emotion.sh/docs/source-maps)
> 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](https://stackoverflow.com/questions/448981/which-characters-are-valid-in-css-class-names-selectors#449000)
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**
```javascript
const brownStyles = css({ color: 'brown' })
```
**Out**
```javascript
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**
```javascript
// BrownView.js
// autoLabel: 'dev-only'
// labelFormat: '[filename]--[local]'
const brownStyles = css({ color: 'brown' })
```
**Out**
```javascript
const brownStyles = /*#__PURE__*/ css(
{ color: 'brown' },
'label:BrownView--brownStyles;'
)
```
`BrownView--brownStyles`'s value would be `css-hash-BrownView--brownStyles`
#### styled
**In**
```javascript
const H1 = styled.h1({
borderRadius: '50%',
transition: 'transform 400ms ease-in-out',
boxSizing: 'border-box',
display: 'flex',
':hover': {
transform: 'scale(1.2)'
}
})
```
**Out**
```javascript
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:
```js
import { anotherExport } from 'my-package';
import { someExport, thisIsTheJsxExport } from 'some-package';
```
An example config:
```json
{
"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`](https://github.com/kentcdodds/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.
```jsx
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'
```
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