API.md

API

Linaria exposes a core css method alongside with small, but just enough amount of helpers. Inside @linaria/core module you can find following methods:

Client APIs

css

String tag for tagged template literals consisting CSS code. The tagged template literal is evaluated to a unique class name by the Babel plugin:

import { css } from '@linaria/core';

const flower = css`
  display: inline;
  color: violet;
`;

// flower === flower__9o5awv –> with babel plugin

All rules inside the template literal are scoped to the class name, including media queries and animations. For example, we can declare CSS animation like so:

import { css } from '@linaria/core';

const box = css`
  animation: rotate 1s linear infinite;

  @keyframes rotate {
    { from: 0deg; }
    { to: 360deg; }
  }
`;

cx(...classNames: Array<string | false | void | null | 0>) => string

Takes a list of class names and returns a concatenated string with the class names. Falsy values are ignored.

import { css, cx } from '@linaria/core';

const cat = css`
  font-weight: bold;
`;

const yarn = css`
  color: violet;
`;

const fun = css`
  display: flex;
`;

function App({ isPlaying }) {
  return <Playground className={cx(cat, yarn, isPlaying && fun)} />;
}

Unlike the classnames library, this doesn't handle objects. If you want need the features of the classnames library, you can use it instead.

styled

Helper to build React components. It allows you to write your components in a similar syntax as styled-components:

The syntax is similar to the css tag. Additionally, you can use function interpolations that receive the component's props:

import { styled } from '@linaria/react';
import colors from './colors.json';

const Container = styled.div`
  background-color: ${colors.background};
  color: ${props => props.color};
  width: ${100 / 3}%;
  border: 1px solid red;

  &:hover {
    border-color: blue;
  }
`;

All rules inside the template literal are scoped to the component, similar to the css tag.

Dynamic function interpolations are replaced with CSS custom properties. A dynamic function interpolation will receive the props of the component as it's arguments and the returned result will be used as the value for the variable. When using this, a tiny helper is imported so that we don't duplicate the code for creating the component in all files.

You can also interpolate a component to refer to it:

const Title = styled.h1`
  font-size: 36px;
`;

const Article = styled.article`
  font-size: 16px;

  /* this will evaluate to the selector that refers to `Title` */
  ${Title} {
    margin-bottom: 24px;
  }
`;

If you want to swap out the tag that's rendered, you can use the as prop:

// Here `Button` is defined as a `button` tag
const Button = styled.button`
  background-color: rebeccapurple;
`;

// You can switch it to use an `a` tag with the `as` prop
<Button as="a" href="/get-started">
  Click me
</Button>;

You can also decorate another styled component with styled:

const Button = styled.button`
  background-color: rebeccapurple;
`;

// The background-color in FancyButton will take precedence
const FancyButton = styled(Button)`
  background-color: black;
`;

Server APIs (@linaria/server)

collect(html: string, css: string) => string

Takes HTML and CSS strings and returns the critical CSS used in the page by analyzing the class names. It can be used to determine critical CSS for server side rendering.

import { collect } from '@linaria/server';

const css = fs.readFileSync('./dist/styles.css', 'utf8');
const html = ReactDOMServer.renderToString(<App />);
const { critical, other } = collect(html, css);

// critical – returns critical CSS for given html
// other – returns the rest of styles

This will only detect critical CSS based on class names, so if you have any other type of selectors, they'll get added to the critical CSS.

Also note that extracting critical CSS this way will change the order of class names. It's not a problem if you're primarily using Linaria for styling. However if you're using a third party framework which imports its own CSS, then it's not recommended to use this helper on the extracted CSS.