@rm66/react-jss

JSS integration with React

React-JSS provides components for JSS as a layer of abstraction. JSS and the default preset are already built in! Try it out in the playground.

Benefits compared to lower level core:

• Theming support.
• Critical CSS extraction.
• Lazy evaluation - sheet is created only when the component will mount.
• Auto attach/detach - sheet will be rendered to the DOM when the component is about to mount, and will be removed when no element needs it.
• A Style Sheet gets shared between all elements.
• Function values and rules are updated automatically with props.

Table of Contents

• Install
• Usage
  • Basic
  • Dynamic Values
  • Theming
  • Server-side rendering
  • React tree traversing
  • Reuse styles in different components
  • The inner component
  • The inner ref
  • Custom setup
  • Decorators
• Contributing
• License

Install

npm install --save react-jss

yarn add react-jss

Usage

React-JSS wraps your component with a higher-order component. It injects a classes prop, which is a simple map of rule names and generated class names. It can act both as a simple wrapping function and as an ES7 decorator.

Try it out in the playground.

Basic

import React from 'react'
import { render } from 'react-dom'
// Import React-JSS
import injectSheet from 'react-jss'

// Create your Styles. Remember, since React-JSS uses the default preset,
// most plugins are available without further configuration needed.
const styles = {
  myButton: {
    color: 'green',
    margin: { // jss-expand gives more readable syntax
      top: 5, // jss-default-unit makes this 5px
      right: 0,
      bottom: 0,
      left: '1rem'
    },
    '& span': { // jss-nested applies this to a child span
      fontWeight: 'bold' // jss-camel-case turns this into 'font-weight'
    }
  },
  myLabel: {
    fontStyle: 'italic'
  }
}

// Define the component using these styles and pass it the 'classes' prop.
// Use this to assign scoped class names.
const Button = ({ classes, children }) => (
  <button className={classes.myButton}>
    <span className={classes.myLabel}>
      {children}
    </span>
  </button>
)

// Finally, inject the stylesheet into the component.
const StyledButton = injectSheet(styles)(Button)
// You can also export the component with
// export default injectSheet(styles)(Button)

const App = () => (
  <StyledButton>
    Submit
  </StyledButton>
)

render(<App />, document.getElementById('root'))

The above code will compile to

<div id="root">
  <button class="Button-myButton-1-25">
    <span class="Button-myLabel-1-26">
      Submit
    </span>
  </button>
</div>

and

.Button-myButton-1-25 {
  color: green;
  margin: 5px 0 0 1rem;
}
.Button-myButton-1-25 span {
  font-weight: bold;
}
.Button-myLabel-1-26 {
  font-style: italic;
}

Dynamic values

You can use function values, function rules and observables out of the box. Function values and function rules will receive a props object once the component receives new props or mounts for the first time.

There are 2 caveats:

1. Static properties are rendered first, so function values will have higher source order specificity.
2. They have a number of limitations regarding the syntax, since they don't run through all plugins right now.

const styles = {
  myButton: {
    padding: props => props.spacing
  },
  myLabel: (props) => ({
    display: 'block',
    color: props.labelColor,
    fontWeight: props.fontWeight,
    fontStyle: props.fontStyle
  })
}

const Button = ({ classes, children }) => (
  <button className={classes.myButton}>
    <span className={classes.myLabel}>
      {children}
    </span>
  </button>
)

Button.defaultProps = {
  spacing: 10,
  fontWeight: 'bold',
  labelColor: 'red'
}

const StyledButton = injectSheet(styles)(Button)

const App = () => (
  <StyledButton fontStyle='italic'>
    Submit
  </StyledButton>
)

The above code will compile to

<div id="root">
  <button class="Button-myButton-1-25">
    <span class="Button-myLabel-1-26">
      Submit
    </span>
  </button>
</div>

and

.Button-myButton-1-25 {
  padding: 10px;
}
.Button-myLabel-1-26 {
  display: block;
  color: red;
  font-weight: bold;
  font-style: italic;
}

Theming

The idea is that you define a theme, wrap your application with ThemeProvider and pass the theme to ThemeProvider. ThemeProvider will pass it over context to your styles creator function and to your props. After that you may change your theme, and all your components will get the new theme automatically.

Under the hood react-jss uses the unified CSSinJS theming solution for React. You can find detailed docs in its repo.

Using ThemeProvider:

• It has a theme prop which should be an object or function:
  • If it is an Object and used in a root ThemeProvider then it's intact and being passed down the react tree.
  • If it is Object and used in a nested ThemeProvider then it's being merged with theme from a parent ThemeProvider and passed down the react tree.
  • If it is Function and used in a nested ThemeProvider then it's being applied to the theme from a parent ThemeProvider. If result is an Object it will be passed down the react tree, throws otherwise.
• ThemeProvider as every other component can render only single child, because it uses React.Children.only in render and throws otherwise.
• Read more about ThemeProvider in theming's documentation.

import React from 'react'
import injectSheet, {ThemeProvider} from 'react-jss'

const Button = ({classes, children}) => (
  <button className={classes.button}>
    <span className={classes.label}>
      {children}
    </span>
  </button>
)

const styles = theme => ({
  button: {
    background: theme.colorPrimary
  },
  label: {
    fontWeight: 'bold'
  }
})

const StyledButton = injectSheet(styles)(Button)

const theme = {
  colorPrimary: 'green'
}

const App = () => (
  <ThemeProvider theme={theme}>
    <StyledButton>I am a button with green background</StyledButton>
  </ThemeProvider>
)

In case you need to access the theme but not render any CSS, you can also use withTheme. It is a Higher-order Component factory which takes a React.Component and maps the theme object from context to props. Read more about withTheme in theming's documentation.

import React from 'react'
import injectSheet, {withTheme} from 'react-jss'

const Button = withTheme(({theme}) => (
  <button>I can access {theme.colorPrimary}</button>
))

Namespaced themes can be used so that a set of UI components should not conflict with another set of UI components from a different library using also react-jss.

import {createTheming} from 'react-jss'

// Creating a namespaced theming object.
const theming = createTheming('__MY_NAMESPACED_THEME__')

const {ThemeProvider: MyThemeProvider} = theming

const styles = theme => ({
  button: {
    background: theme.colorPrimary
  }
})

const theme = {
  colorPrimary: 'green'
}

const Button = ({classes, children}) => (
  <button className={classes.button}>
    {children}
  </button>
)

// Passing namespaced theming object inside injectSheet options.
const StyledButton = injectSheet(styles, { theming })(Button)

// Using namespaced ThemeProviders - they can be nested in any order
const App = () => (
  <OtherLibraryThemeProvider theme={otherLibraryTheme}>
    <OtherLibraryComponent />
    <MyThemeProvider theme={theme}>
      <StyledButton>Green Button</StyledButton>
    </MyThemeProvider>
  <OtherLibraryThemeProvider>
)

Server-side rendering

After the application is mounted, you should remove the style tag used by critical CSS rendered server-side.

import {renderToString} from 'react-dom/server'
import {JssProvider, SheetsRegistry} from 'react-jss'
import MyApp from './MyApp'

export default function render(req, res) {
  const sheets = new SheetsRegistry()

  const body = renderToString(
    <JssProvider registry={sheets}>
      <MyApp />
    </JssProvider>
  )

  // Any instances of `injectSheet` within `<MyApp />` will have gotten sheets
  // from `context` and added their Style Sheets to it by now.

  return res.send(renderToString(
    <html>
      <head>
        <style type="text/css">
          {sheets.toString()}
        </style>
      </head>
      <body>
        {body}
      </body>
    </html>
  ))
}

React tree traversing

For traversing the React tree outside of the HTML rendering, you should add disableStylesGeneration property.

import * as React from 'react'
import * as ReactDOM from 'react-dom'
import bootstrapper from 'react-async-bootstrapper'

import { JssProvider } from 'react-jss'
import MyApp from './MyApp'

const App = ({ disableStylesGeneration }) => (
  <JssProvider disableStylesGeneration>
    <MyApp />
  </JssProvider>
)

async function main() {
  await bootstrapper(<App disableStylesGeneration />)
  ReactDOM.render(<App />, document.getElementById('root'))
}

main()

Reuse styles in different components

In order to reuse the same styles and the same generated style sheet between 2 entirely different and unrelated components, we suggest extracting a renderer component and reusing that.

const styles = {
  button: {
    color: 'red'
  }
}
const RedButton = injectSheet(styles)(({classes, children}) => (
  <button className={classes.button}>{children}</button>
))

const SomeComponent1 = () => (
  <div>
    <RedButton>My red button 1</RedButton>
  </div>
)

const SomeComponent2 = () => (
  <div>
    <RedButton>My red button 2</RedButton>
  </div>
)

Alternatively you can create own Style Sheet and use the composes feature. Also you can mix in a common styles object, but take into account that it can increase the overall CSS size.

The inner component

const InnerComponent = () => null
const StyledComponent = injectSheet(styles, InnerComponent)
console.log(StyledComponent.InnerComponent) // Prints out the inner component.

The inner ref

In order to get a ref to the inner element, use the innerRef prop.

const InnerComponent = () => null
const StyledComponent = injectSheet({})(InnerComponent)

<StyledComponent innerRef={(ref) => {console.log(ref)}} />

If you are using React 16.3 or higher we also support forwarding the ref to the InnerComponent.

const InnerComponent = () => null
const StyledComponent = injectSheet({})(InnerComponent)

<StyledComponent ref={(ref) => {console.log(ref)}} />

Custom setup

If you want to specify a JSS version and plugins to use, you should create your own JSS instance, setup plugins and pass it to JssProvider.

import {create as createJss} from 'jss'
import {JssProvider} from 'react-jss'
import vendorPrefixer from 'jss-vendor-prefixer'

const jss = createJss()
jss.use(vendorPrefixer())

const Component = () => (
  <JssProvider jss={jss}>
    <App />
  </JssProvider>
)

You can also access the JSS instance being used by default.

import {jss} from 'react-jss'

Multi-tree setup

In case you render multiple react rendering trees in one application, you will get class name collisions, because every JssProvider rerender will reset the class names generator. If you want to avoid this, you can share the class names generator between multiple JssProvider instances.

Note: in case of SSR, make sure to create a new generator for each request. Otherwise class names will become indeterministic and at some point you may run out of max safe integer numbers.

import {createGenerateClassName, JssProvider} from 'react-jss'

const generateClassName = createGenerateClassName()

const Component = () => (
  <div>
    <JssProvider generateClassName={generateClassName}>
      <App1 />
    </JssProvider>
    <JssProvider generateClassName={generateClassName}>
      <App2 />
    </JssProvider>
  </div>
)

You can also additionally use the classNamePrefix prop in order to add the app/subtree name to each class name. This way you can see which app generated a class name in the DOM view.

import {JssProvider} from 'react-jss'

const Component = () => (
  <div>
    <JssProvider classNamePrefix="App1-">
      <App1 />
    </JssProvider>
    <JssProvider classNamePrefix="App2-">
      <App2 />
    </JssProvider>
  </div>
)

Decorators

Beware that decorators are stage-2 proposal, so there are no guarantees that decorators will make its way into language specification. Do not use it in production. Use it at your own risk and only if you know what you are doing.

You will need babel-plugin-transform-decorators-legacy.

import React, {Component} from 'react'
import injectSheet from 'react-jss'

const styles = {
  button: {
    backgroundColor: 'yellow'
  },
  label: {
    fontWeight: 'bold'
  }
}

@injectSheet(styles)
export default class Button extends Component {
  render() {
    const {classes, children} = this.props
    return (
      <button className={classes.button}>
        <span className={classes.label}>
          {children}
        </span>
      </button>
    )
  }
}

Injection order

Style tags are injected in the exact same order as the injectSheet() invocation. Source order specificity is higher the lower style tag is in the tree, therefore you should call injectSheet of components you want to override first.

Example

// Will render labelStyles first.
const Label = injectSheet(labelStyles)(({children}) => <label>{children}</label>)
const Button = injectSheet(buttonStyles)(() => <button><Label>my button</Label></button>)

Whitelist injected props

By default "classes" and "theme" are going to be injected to the child component over props. Property theme is only passed when you use a function instead of styles object. If you want to whitelist some of them, you can now use option inject. For e.g. if you want to access the StyleSheet instance, you need to pass {inject: ['sheet']} and it will be available as props.sheet.

All user props passed to the HOC will still be forwarded as usual.

// Only `classes` prop will be passed by the ReactJSS HOC now. No `sheet` or `theme`.
const Button = injectSheet(styles, {inject: ['classes', 'sheet']})(
  ({classes}) => <button>My button</button>
)

Contributing

See our contribution guidelines.

License

MIT