styled-jsx

Full, scoped and component-friendly CSS support for JSX (rendered on the server or the client).

Usage

Firstly, install the package:

$ npm install --save styled-jsx

Next, add styled-jsx/babel to plugins in your babel configuration:

{
  "plugins": [
    "styled-jsx/babel"
  ]
}

Now add <style jsx> to your code and fill it with CSS:

export default () => (
  <div>
    <p>only this paragraph will get the style :O</p>
    { /* you can include <Component />s here that include
         other <p>s that don't get unexpected styles! */ }
    <style jsx>{`
      p {
        color: red;
      }
    `}</style>
  </div>
)

Features

• Full CSS support, no tradeoffs in power
• Runtime size of just 500 bytes
• Complete isolation: Selectors, animations, keyframes
• Built-in CSS-prefixing
• Very fast, minimal and efficient transpilation (see below)
• High-performance runtime-CSS-injection when not server-rendering
• Future-proof: Equivalent to server-renderable "Shadow CSS"
• Works like the deprecated <style scoped>, but the styles get injected only once per component

How It Works

The example above transpiles to the following:

import _JSXStyle from 'styled-jsx/style'

export default () => (
  <div data-jsx='cn2o3j'>
    <p data-jsx='cn2o3j'>only this paragraph will get the style :O</p>
    <_JSXStyle data-jsx='cn2o3j' css={`p[data-jsx=cn2o3j] {color: red;}`} />
  </div>
)

Why It Works Like This

Data attributes give us style encapsulation and _JSXStyle is heavily optimized for:

• Injecting styles upon render
• Only injecting a certain component's style once (even if the component is included multiple times)
• Removing unused styles
• Keeping track of styles for server-side rendering (discussed in the next section)

Targetting The Root

Notice that the parent <div> above also gets a data-jsx atribute. We do this so that you can target the "root" element, in the same manner that :host works with Shadow DOM.

If you want to target only the host, we suggest you use a class:

export default () => (
  <div className="root">
    <style jsx>{`
      .root {
        color: green;
      }
    `}</style>
  </div>
)

Global styles

To skip scoping entirely, you can make the global-ness of your styles explicit by adding global.

export default () => (
  <div>
    <style jsx global>{`
      body {
        background: red
      }
    `}</style>
  </div>
)

The advantage of using this over <style> is twofold: no need to use dangerouslySetInnerHTML to avoid escaping issues with CSS and take advantage of styled-jsx's de-duping system to avoid the global styles being inserted multiple times.

Global selectors

Sometimes it's useful to skip prefixing. We support :global(), inspired by css-modules.

This is very useful in order to, for example, generate an unprefixed class that you can pass to 3rd-party components. For example, to style react-select which supports passing a custom class via optionClassName:

import Select from 'react-select'
export default () => (
  <div>
    <Select optionClassName="react-select" />

    <style jsx>{`
      /* "div" will be prefixed, but ".react-select" won't */
      div :global(.react-select) {
        color: red
      }
    `}</style>
  </div>
)

Server-Side Rendering

In the server rendering pipeline, you can obtain the entire CSS of all components by invoking flush:

import flush from 'styled-jsx/flush'

// …
// <render here>
// …

const styles = flush()

for (let id in styles) {
  const css = styles[id]
  console.log(id, css)
}

This API is also available on the client: Instead of returning the CSS text, it returns a reference to the automatically generated <style> tag.

This is useful for performing diffs of elements between top-level render() calls, and ditching style elements that are no longer being used.

Credits

• Pedram Emrouznejad (rijs) suggested attribute selectors over my initial class prefixing idea.
• Sunil Pai (glamor) inspired the use of murmurhash2 (minimal and fast hashing) and an efficient style injection logic.
• Sultan Tarimo built stylis.js, a super fast and tiny CSS parser and compiler.
• Max Stoiber (styled-components) proved the value of retaining the familiarity of CSS syntax and pointed me to the very efficient stylis compiler (which we forked to very efficiently append attribute selectors to the user's css)
• Yehuda Katz (ember) convinced me on Twitter to transpile CSS as an alternative to CSS-in-JS.
• Evan You (vuejs) discussed his Vue.js CSS transformation with me.
• Henry Zhu (babel) helpfully pointed me to some important areas of the babel plugin API.

Author

Guillermo Rauch (@rauchg) - ▲ZEIT