Components As Selectors

Referring to other components

This is a web-specific API and you won't be able to use it in react-native.

There are many ways to apply contextual overrides to a component's styling. That being said, it rarely is easy without rigging up a well-known targeting CSS selector paradigm and then making them accessible for use in interpolations.

styled-components solves this use case cleanly via the "component selector" pattern. Whenever a component is created or wrapped by the styled() factory function, it is also assigned a stable CSS class for use in targeting. This allows for extremely powerful composition patterns without having to fuss around with naming and avoiding selector collisions.

A practical example: here, our Icon component defines its response to the parent Link being hovered:

const Link = styled.a`
  display: flex;
  align-items: center;
  padding: 5px 10px;
  background: papayawhip;
  color: #BF4F74;
`;

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

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

const Label = styled.span`
  display: flex;
  align-items: center;
  line-height: 1.2;

  &::before {
    content: '◀';
    margin: 0 10px;
  }
`;

render(
  <Link href="#">
    <Icon viewBox="0 0 20 20">
      <path d="M10 15h8c1 0 2-1 2-2V3c0-1-1-2-2-2H2C1 1 0 2 0 3v10c0 1 1 2 2 2h4v4l4-4zM5 7h2v2H5V7zm4 0h2v2H9V7zm4 0h2v2h-2V7z"/>
    </Icon>
    <Label>Hovering my parent changes my style!</Label>
  </Link>
);

We could have nested the color-changing rule within our Link component, but then we'd have to consider both sets of rules to understand why Icon behaves as it does.

Caveat

This behaviour is only supported within the context of Styled Components: attempting to mount B in the following example will fail because component A is an instance of React.Component not a Styled Component.

class A extends React.Component {
  render() {
    return <div />
  }
}

const B = styled.div`
  ${A} {
  }
`

The error thrown - Cannot call a class as a function - occurs because the styled component is attempting to call the component as an interpolation function.

However, wrapping A in a styled() factory makes it eligible for interpolation -- just make sure the wrapped component passes along className.

class A extends React.Component {
  render() {
    return <div className={this.props.className} />
  }
}

const StyledA = styled(A)``

const B = styled.div`
  ${StyledA} {
  }
`