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useStyles() - Styles

Styling is an important part of the design of a web application. Qwik is responsible for loading the style information when a component is mounted. Use useStyles$() to tell Qwik which style should be loaded.

Why not inline styles?

A naive way to ensure that a component has the correct styles loaded is to inline the style information into a component like so.

export const MyComponent = () => {
  return (
    <>
    <style>.my-class { color: red; }</style>
      My Component
    </>
  );
}

The problem with this approach is that we will load styles twice.

  1. The styles are inserted into the HTML as part of the SSR.
  2. Then when the component is invalidated and needs to be re-rendered, the styles are loaded again because they are inlined.

What is needed is to load the styles independently from the component. This is what useStyles$() is for. There are two scenarios:

  1. The component is rendered on the server and the styles are inserted into <head> as part of the SSR.
    • Adding a new instance of a component to the application does not require that we load the styles as they are already included as part of SSR.
  2. The component is rendered on the client for the first time. In that case, the new component does not have styles in the <head> as the component was not part of SSR.
    • Adding a new component that was not part of SSR requires that styles are loaded and inserted into <head>.

Example

This example contains two components:

  1. <Sibling>: The <Sibling> component is pre-rendered on the server. Because it is pre-rendered, it has styles in the <head> as it was part of SSR. Adding additional <Sibling> components does not require any styles to be loaded.
  2. <Child>: The <Child> component can be added by clicking the toggle button. Because it was not part of the SSR pre-rendered, it does not have styles in the <head>. Toggling <Child> requires that styles are loaded.

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