Improving React App Performance with Lazy Loading
Tags: webdev, react, beginners, frontend
Published: 2023-04-21 16:54:19

When building React applications, it's important to consider performance. Slow applications can have a negative impact on user experience, specially on slower internet connections. One technique for improving performance is lazy loading. 
According to the official documentation of React JS 

> lazy lets you defer loading component’s code until it is rendered for the first time.
`const SomeComponent = lazy(load)`

## Why and When to Use Lazy Loading
Lazy loading can provide a number of benefits for your React application. By deferring or postponing the loading of non-critical components, one can reduce the initial bundle size and improve the time-to-interactive (a metric used to measure how long it takes for a web page to become fully interactive for the user).

It is an effective technique to use when you have large or infrequently used components in your React application. For example, in a multi-step form with multiple sections, instead of loading all the code for each section upfront, you can use lazy loading to load each section's code only when the user needs it. This helps to reduce the initial load time of the application.
## How to Use Lazy Loading in React
To use lazy loading in React, you can use the lazy(load) function and the Suspense component.
- lazy takes a parameter load which is a function that returns a promise. React will not execute the load function until the first time the returned component is rendered. Once React calls the load function, it will wait for it to resolve and then render the resolved value as a React component. 

Here's an example of how you might use lazy loading to defer the loading of a component called MyComponent:

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

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

function App() {
  return (
    <div>
      <Suspense fallback={<div>Loading...</div>}>
        <MyComponent />
      </Suspense>
    </div>
  );
}
```
In this example, the lazy() function is used to import the MyComponent module lazily, so that its code is only loaded when it's actually needed. The Suspense component is used to display a fallback UI while the code is being loaded. In this case, the fallback UI is simply the text "Loading...".
## Disadvantages of Using Lazy Loading
While lazy loading can provide significant performance benefits, it's important to use it judiciously and avoid overloading the browser with too many lazy-loaded components. Here are some potential disadvantages to consider:

- **Increased complexity:** Lazy loading adds an additional layer of complexity to your codebase, which can make it harder to understand and maintain.
- **Delayed rendering:** Because the code for lazy-loaded components is not loaded until it's needed, there may be a delay in rendering those components. This can result in a slower initial load time for the component.
- **Poor user experience on slow connections:** If a user is on a slow internet connection, lazy loading may result in a poor user experience, as components may take longer to load and render.

## Conclusion
Lazy loading is a powerful technique for improving the performance of your React applications. Using it can lead to a faster and more responsive application and improve user experience. However, it's important to weigh the potential advantages and disadvantages of lazy loading to avoid overloading the browser with too many lazy-loaded components.

## References
[lazy](https://react.dev/reference/react/lazy)