Lazy loading and code splitting are optimization techniques used in web development to improve performance, especially for large applications and it is required when applying for front-end developer roles.

1. Lazy Loading

Lazy loading is a strategy to defer loading resources (like images, scripts, or components) until they are actually needed. This helps reduce the initial load time of the webpage, as only essential resources are loaded up front. For example, a web page may load just the content the user sees initially, and then load more content as the user scrolls down or navigates to other parts of the app.

In React, lazy loading can be implemented using React.lazy() and Suspense for loading components only when they are needed:

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

function App() {
  return (
    <Suspense fallback={<div>Loading...</div>}>
      <LazyComponent />
    </Suspense>
  );
}

2. Code Splitting

Code splitting is the process of breaking up your application’s code into smaller bundles, so that only the necessary code is loaded initially. This complements lazy loading by ensuring that only the code for the current view or feature is loaded, rather than loading the entire application at once.

Tools like Webpack or Vite provide automatic code splitting. In React, it’s typically done with dynamic import() statements, which enables splitting out parts of your app (like individual components or routes) into separate chunks.

For example, you might load specific routes as separate bundles like this:

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

<Route path="/lazy" component={LazyComponent} />

Together, lazy loading and code splitting can significantly enhance the performance of large apps, making them faster and more efficient.