React.lazy, What and how to use in your app

#javascript #react

React 16.6 is out and with it comes the new Lazy API. The Rreact.lazy function lets you render a dynamic import as a regular component.

React.lazy takes a function that must call a dynamic import(). This must return a Promise which resolves to a module with a default export containing a React component.

Usage:

const LazyComponent = React.lazy(() => import('./Component'));

Show a fallback with Suspense

Wrap the component where it's used with Suspense and pass a fallback. The fallback prop accepts any React elements that you want to render while waiting for the component to load.

<Suspense fallback={<div>Loading Component...</div>}>
  <LazyComponent />
</Suspense>

I made a simple example to show

The app shows a Press Me!! button which when pressed fetches a random user data from randomuser then loads and renders the User component.

const User = React.lazy(() => import('./User'));

....

<React.Suspense fallback={<div>Loading Component...</div>}>
  {user && <User user={user}/>}
  {loading ? (
    <div>Loading User...</div>
  ) : (
    !user && <button onClick={this.loadUser}>Press Me!!</button>
  )}
</React.Suspense>

Live: react-lazy-example
Code: github

Run the app, open your Network tab in Dev console, Press the button and see the lazily loaded javascript chunk. 🎉🎉

Latest comments (5)

hafidzamr • Oct 12 '19

using React.lazy every import component is effective? I'm so confused about what condition should use Reac.lazy

Constantine Antonakos • Mar 7 '19 • Edited

Would this be a good use case for lazy loading a component that imports a large npm package? In other words, I used to dynamically import these type of packages with import() in the React component lifecycle before rendering something.