What method would you use to check and improve speed of React app?

To check and improve the speed of a React app, one can use various methods.

One of the most common methods is to use the Chrome DevTools to analyze the performance of the app. The DevTools provide a Performance tab that can be used to record and analyze the performance of the app. This tab provides a detailed timeline of the app's activity, including the time taken for rendering, scripting, painting, and other activities. By analyzing this timeline, one can identify the bottlenecks and optimize the app's performance.

Another method to improve the speed of a React app is to use code splitting. Code splitting is a technique that involves breaking down the app's code into smaller chunks that can be loaded on demand. This technique can significantly reduce the initial load time of the app and improve its performance. React provides built-in support for code splitting through its dynamic import() function. This function allows developers to load components and modules on demand, rather than loading them all at once.

In addition to these methods, one can also optimize the app's rendering performance by using techniques such as memoization, shouldComponentUpdate, and PureComponent.

Memoization is a technique that involves caching the results of expensive function calls, so that they can be reused later.

shouldComponentUpdate is a lifecycle method that can be used to prevent unnecessary re-renders of components.

PureComponent is a variant of the React component that implements shouldComponentUpdate automatically, based on a shallow comparison of props and state.

By using these techniques, one can optimize the rendering performance of the app and improve its overall speed.

// Example of code splitting using dynamic import()

import React, { lazy, Suspense } from 'react';

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

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