An “artificial” CSS-in-JS for those that want it all.

astroturf

astroturf lets you write CSS in your JavaScript files without adding any runtime layer, and with your existing CSS processing pipeline.

• Zero runtime CSS-in-JS. Get many of the same benefits as CSS-in-JS, but without the loss of flexibility in requiring framework-specific CSS processing, and while keeping your CSS fully static with no runtime style parsing.
• Use your existing tools – Sass, PostCSS, Less – but still write your style definitions in your JavaScript files
• Whole component in the single file. Write CSS in a template literal, then use it as if it were in a separate file

• Usage
• Component API
• css prop
• Component API Goals and Non-Goals
• Composition, variables, etc?
• Referring to other Components
• Sharing values between styles and JavaScript
• Keyframes and global
• Attaching Additional Props
• as prop
• Setup
  • Options
  • Use with Gatsby
  • Use with Parcel
  • Use with Preact
  • Use with Next.js
  • Use without webpack

Usage

import React from 'react';
import { css } from 'astroturf';

const styles = css`
  .button {
    color: black;
    border: 1px solid black;
    background-color: white;
  }
`;

export default function Button({ children }) {
  return <button className={styles.button}>{children}</button>;
}

When processed, the css block will be extracted into a .css file, taking advantage of any and all of the other loaders configured to handle css.

It even handles statically analyzable interpolations!

import { css } from 'astroturf';

const margin = 10;
const height = 50;
const bottom = height + margin;

const styles = css`
  .box {
    height: ${height}px;
    margin-bottom: ${margin}px;
  }

  .footer {
    position: absolute;
    top: ${bottom}px;
  }
`;

Component API

For those that want something a bit more like styled-components or Emotion, there is a component API!

import styled, { css } from 'astroturf';

const Button = styled('button')`
  color: black;
  border: 1px solid black;
  background-color: white;

  &.primary {
    color: blue;
    border: 1px solid blue;
  }

  &.color-green {
    color: green;
  }
`;

You can render this with:

render(
  <Button primary color="green">
    A styled button
  </Button>,
  mountNode,
);

The above transpiles to something like:

const styles = css`
  .button {
    color: black;
    border: 1px solid black;
    background-color: white;

    &.primary {
      color: blue;
      border: 1px solid blue;
    }

    &.color-green {
      color: green;
    }
  }
`;

function Button({ primary, color, className, ...props }) {
  return (
    <button
      {...props}
      className={classNames(
        className,
        styles.button,
        primary && styles.primary,
        color === 'green' && styles.colorGreen,
      )}
    />
  );
}

css prop

In addition to the styled helper, styles can be defined directly on components via the css prop. You first need to enable this feature via the enableCssProp option in your loader config

function Button({ variant, children }) {
  return (
    <button
      variant={variant}
      css={css`
        color: black;
        border: 1px solid black;
        background-color: white;

        &.variant-primary {
          color: blue;
          border: 1px solid blue;
        }

        &.variant-secondary {
          color: green;
        }
      `}
    >
      {children}
    </button>
  );
}

Styles are still extracted to a separate file, any props matching other defined classes are passed to the classNames() library. At runtime styled() returns a React component with the static CSS classes applied. You can check out the “runtime” it just creates a component.

There are a whole bucket of caveats of course, to keep the above statically extractable, and limit runtime code.

• We assume you are using css-modules in your css pipeline to return classes from the style files, we don’t do any of that ourselves.
• Prop value handling requires the nesting transform
• All “top level” styles have any @import statements hoisted up (via a regex)

Component API Goals and Non-Goals

The goal of this API is not to mimic or reimplement the features of other css-in-js libraries, but to provide a more ergonomic way to write normal css/less/sass next to your javascript.

What does that mean? css-in-js libraries are a replacement for css preprocessors, in that they provide ways of doing variables, composition, mixins, imports etc. Usually they accomplish this by leaning on JS language features where appropriate, and adding their own domain-specific language bits when needed.

astroturf doesn’t try to do any of that because it’s not trying to replace preprocessors, but rather, make component-centric javascript work better with existing styling tooling. This means at a minimum it needs to scope styles to the component (handled by css-modules) and map those styles to your component’s API (props), which is what the above API strives for.

This approach gains us:

• No additional work to extract styles for further optimization (autoprefixer, minifying, moving them to a CDN, etc)
• The smallest runtime, it’s essentially zero
• Blazing Fast™ because there is zero runtime evaluation of styles
• Leverage the well-trod and huge css preprocesser ecosystems

It also means we sacrifice:

• A fine-grained style mapping to props. Props map to classes, its all very BEM-y but automated
• Dynamism in sharing values between js and css
• A unified JS-only headspace, you still need to think in terms of JS and CSS

Composition, variables, etc?

How you accomplish that is mostly up to your preprocessor. Leverage Sass variables, or Less mixins, or postcss nesting polyfills, or whatever. The css you’re writing is treated exactly like a normal style file so all the tooling you’re used to works as expected. For composition, specifically around classes, you can also use css-modules composes to compose styles and interpolation;

// Button.js

const helpers = css`
  .heavy {
    font-weight: 900;
  }
`;

const Title = styled('h3')`
  composes: ${helpers.heavy};

  font-size: 12%;
`;

You don’t have to define everything in a .js file. Where it makes sense just use normal css (or any other file type).

// mixins.scss
@mixin heavy() {
  font-weight: 900;
}

and then:

// Button.js
const Title = styled('h3')`
  @import './mixins.scss';

  @include heavy();
  font-size: 12%;
`;

Referring to other Components

One limitation to fully encapsulated styles is that it’s hard to contextually style components without them referencing each other. In astroturf you can use a component in a selector as if it were referencing a class selector.

Note: Referencing stylesheets or styled components from other files has a few caveats: cross-file-dependencies

const Link = styled.a`
  display: flex;
  align-items: center;
  padding: 5px 10px;
  background: papayawhip;
  color: palevioletred;
`;

const Icon = styled.svg`
  flex: none;
  transition: fill 0.25s;
  width: 48px;
  height: 48px;

  ${Link}:hover & {
    fill: rebeccapurple;
  }
`;

Sharing values between styles and JavaScript

We’ve found that in practice, you rarely have to share values between the two, but there are times when it’s very convenient. Astroturf ofters two ways to do this, the first is string interpolations.

const DURATION = 500;

const ColorTransition = styled('nav')`
  color: red;
  transition: color ${DURATION}ms;

  &.blue {
    color: blue;
  }
`;

class App extends React.Component {
  state = { blue: false }
  toggle = () => {
    this.setState(s => ({ blue: !s.blue }), () => {
      setTimeout(() => console.log('done!'), DURATION)
    })
  }
  render() {
    const { blue } = this.state
    <div>
      <ColorTransition blue={blue} />
      <button onClick={this.toggle}>Toggle Color</button>
    </div>;
  }
}

This works great for local variables, since the compiler can determine their value at compile time and share them. For cases when you want to share things a bit more globally, such as in a theme, we recommend leaning on your css preprocesser again.

css-modules provides a syntax for exporting values from styles, generally this is used for class names, but you can leverage it for whatever values you want. Combined with something like Sass’s variables it ends up being a powerful tool.

const breakpointValues = css`
  @import '../styles/theme';

  :export {
    @each $breakpoint, $px in $grid-breakpoints {
      #{$breakpoint}: $px;
    }
  }
`

class Responsive extends React.Component {
  state = { isMobile: false }

  componentDidMount() {
    this.setState({
      isMobile: window.clientWidth < parseInt(breakpoints.md, 10)
    })
  }

  render() {
    const { isMobile } = this.state
    <div>
      {isMobile ? 'A small screen!' : 'A big screen!'}
    </div>;
  }
}

Keyframes and global

Everything in css will be used as normal CSS Modules styles. So, if you need to insert some CSS without isolation (like reset with postcss-normalize):

css`
  @import-normalize;

  :global(.btn) {
    background: blue;
  }
`;

With postcss-nested you can add keyframes to specific component (and keyframes name will not be global):

const Loader = styled('div')`
  animation-name: rotation;
  animation-duration: 1s;
  animation-timing-function: linear;
  animation-iteration-count: infinite;

  @keyframes rotation {
    to {
      transform: rotate(360deg);
    }
  }
`;

Attaching Additional Props

A common task with styled components is to map their props or set default values. astroturf cribs from Styled Components, by including an attrs() api.

import styled from 'astroturf';

// Provide a default `type` props
const PasswordInput = styled('input').attrs({
  type: 'password',
})`
  background-color: #ccc;
`;

// Map the incoming props to a new set of props
const TextOrPasswordInput = styled('input').attrs(
  ({ isPassword, ...props }) => ({
    ...props,
    type: isPassword ? 'password' : 'text',
  }),
)`
  background-color: #ccc;
`;

Because attrs() is resolved during render you can use hooks in them! We even do some magic in the non-function signature so that it works.

const Link = styled('a').attrs(props => ({
  href: useRouter().createHref(props.to)
}))`
  color: blue;
`);

// astroturf will automatically compile to a function
// when using a plain object so that the hooks
// are only evaluated during render
const Link = styled(MyLink).attrs({
  router: useRouter()
})`
  color: blue;
`);

as prop

astroturf supports the as prop to control the underlying element type at runtime.

const Button = styled('button')`
  color: red;
`

<Button as="a" href="#link"/>

This feature is only enabled by default for host components, e.g. native DOM elements. We do this to prevent annoying conflicts with other UI libraries like react-bootstrap or semantic-ui which also use the the as prop. If you want to enable it for any styled component you can do so via the allowAs option.

const StyledFooter = styled(Footer, { allowAs: true })`
  color: red;
`;

Setup

If you want the simplest, most bare-bones setup you can use the included css-loader which will setup css-modules and postcss-nested. This is the minimum setup necessary to get it working. Any options passed to the loader are passed to the official webpack css-loader

{
  module: {
    rules: [
      {
        test: /\.css$/,
        use: ['style-loader', 'astroturf/css-loader'],
      },
      {
        test: /\.jsx?$/,
        use: ['babel-loader', 'astroturf/loader'],
      },
      // astroturf works out of the box with typescript (.ts or .tsx files).
      {
        test: /\.tsx?$/,
        use: ['ts-loader', 'astroturf/loader'],
      },
    ];
  }
}

You can add on here as you would normally for additional preprocesser setup. Here’s how you might set up Sass:

{
  module: {
    rules: [
      {
        test: /\.module\.scss$/,
        use: ['style-loader', 'astroturf/css-loader', 'sass-loader'],
      },
      {
        test: /\.jsx?$/,
        use: [
          'babel-loader',
          {
            loader: 'astroturf/loader',
            options: { extension: '.module.scss' },
          },
        ],
      },
    ],
  }
}

You can also skip the included css-loader entirely if your preprocessor handles nesting out of the box (like most do).

[
  {
    test: /\.module\.scss$/,
    use: ['style-loader', 'css-loader?modules=true', 'sass-loader'],
  },
  ...
]

Options

astroturf accepts a few query options.

• tagName: (default: 'css') The tag identifier used to locate inline css literals and extract them.
• styledTag: (default: 'styled') The tag identifier used to locate components.
• extension: (default: '.css') the extension used for extracted “virtual” files. Change to whatever file type you want webpack to process extracted literals as.
• enableCssProp: (default: false) compiles css props to styled components.

Note: astroturf expects uncompiled JavaScript code, If you are using babel or Typescript to transform tagged template literals, ensure the loader runs before babel or typescript loaders.

Use with Parcel

Add these lines to package.json to work with Parcel builder:

  "postcss": {
    "modules": true,
    "plugins": [
      "postcss-nested"
    ]
  },
  "babel": {
    "plugins": [
      "astroturf/plugin"
    ]
  },

Use with Gatsby

See gatsby-plugin-astroturf

Use with Preact

Add these lines to package.json to work with Preact:

  "browser": {
    "react": "preact"
  },

Use with Next.js

See example

Use without webpack

If you aren’t using webpack and still want to define styles inline, there is a babel plugin for that.

Config shown below with the default options.

// babelrc.js
module.exports = {
  plugins: [
    [
      'astroturf/plugin',
      {
        tagName: 'css',
        extension: '.css',
        writeFiles: true, // Writes css files to disk using the result of `getFileName`
        getFileName(hostFilePath, pluginsOptions) {
          const basepath = join(
            dirname(hostFilePath),
            basename(hostFilePath, extname(hostFilePath)),
          );
          return `${basepath}__extracted_style${opts.extension}`;
        },
      },
    ],
  ],
};

The extracted styles are also available on the metadata object returned from babel.transform.

const { metadata } = babel.transformFile(myJsfile);

metadata['astroturf'].styles; // [{ path, value }]