css-to-react-native-transform

A lightweight wrapper on top of css-to-react-native to allow valid CSS to be turned into React Native Stylesheet objects.

To keep things simple it only transforms class selectors (e.g. .myClass {}) and grouped class selectors (e.g. .myClass, .myOtherClass {}). Parsing of more complex selectors can be added as a new feature behind a feature flag (e.g. transform(css, { parseAllSelectors: true })) in the future if needed.

Example:

.myClass {
  font-size: 18px;
  line-height: 24px;
  color: red;
}

.other {
  padding: 1rem;
}

is transformed to:

{
  myClass: {
    fontSize: 18,
    lineHeight: 24,
    color: "red"
  },
  other: {
    paddingBottom: 16,
    paddingLeft: 16,
    paddingRight: 16,
    paddingTop: 16
  }
}

API

Transform CSS

import transform from "css-to-react-native-transform";
// or const transform = require("css-to-react-native-transform").default;

transform(`
  .foo {
    color: #f00;
  }
`);

↓ ↓ ↓ ↓ ↓ ↓

{
  foo: {
    color: "#f00";
  }
}

CSS Modules :export block

Parsing the CSS Modules (ICSS) :export is supported. The :export is often used to share variables from CSS or from a preprocessor like Sass/Less/Stylus to Javascript:

transform(`
  .foo {
    color: #f00;
  }

  :export {
    myProp: #fff;
  }
`);

↓ ↓ ↓ ↓ ↓ ↓

{
  foo: {
    color: "#f00";
  },
  myProp: "#fff";
}

CSS Media Queries (experimental)

The API and parsed syntax for CSS Media Queries might change in the future

transform(
  `
  .container {
    background-color: #f00;
  }

  @media (orientation: landscape) {
    .container {
      background-color: #00f;
    }
  }
`,
  { parseMediaQueries: true },
);

↓ ↓ ↓ ↓ ↓ ↓

{
  __mediaQueries: {
    "@media (orientation: landscape)": [{
      expressions: [
        {
          feature: "orientation",
          modifier: undefined,
          value: "landscape",
        },
      ],
      inverse: false,
      type: "all",
    }],
  },
  container: {
    backgroundColor: "#f00",
  },
  "@media (orientation: landscape)": {
    container: {
      backgroundColor: "#00f",
    },
  },
}

You can also speficy a platform as the media query type ("android", "dom", "ios", "macos", "web", "windows"):

transform(
  `
  .container {
    background-color: #f00;
  }

  @media android and (orientation: landscape) {
    .container {
      background-color: #00f;
    }
  }
`,
  { parseMediaQueries: true },
);

CSS Viewport Units (experimental)

When CSS Viewport Units are used, a special __viewportUnits feature flag is added to the result. This is done so that the implementation that transforms viewport units to pixels knows that the style object has viewport units inside it, and can avoid doing extra work if the style object does not contain any viewport units.

transform(`.foo { font-size: 1vh; }`);

↓ ↓ ↓ ↓ ↓ ↓

{
   __viewportUnits: true,
  foo: {
    fontSize: "1vh";
  }
}

Limitations

• For rem unit the root element font-size is currently set to 16 pixels. A setting needs to be implemented to allow the user to define the root element font-size.
• There is also support for the box-shadow shorthand, and this converts into shadow- properties. Note that these only work on iOS.

Dependencies

This library has the following packages as dependencies:

• css - CSS parser / stringifier
• css-mediaquery - Parses and determines if a given CSS Media Query matches a set of values.
• css-to-react-native - Convert CSS text to a React Native stylesheet object