Lazy Loading Lazy Loading Trap Avoiding Best Practices in Angular

introduction

Performance optimization has always been a key issue in the development of Angular applications. One of them is using Lazy Loading to delay loading certain parts of the application to reduce initial loading time and improve user experience. However, developers can get stuck in some common mistakes when implementing Lazy Loading, which this article will cover in detail and how to avoid them.

Why use Lazy Loading?

Before diving into the pitfalls of Lazy Loading, let's first understand why Lazy Loading is used. Lazy Loading is a technology that loads modules or components on demand, which can divide an application into small pieces and load the corresponding code only when the user navigates to a specific part. This helps reduce initial loading time and improve application performance.

In Angular, Lazy Loading is usually used with routing. Through routing configuration, we can map different routes to different modules or components to achieve on-demand loading. But it is in this process that developers may make some common mistakes.

Error 1: Avoid static import of Lazy Loaded code

In order for Code Splitting and Lazy Loading to take effect, the main app bundle should not contain any static import of code that you wish to delay load. Static imports cause the build tool to notice that the code is already included in the main application bundle, thus not generating a separate chunk of code (chunk).

This error may occur when we perform a static import in the main application to access the code that we wish to delay loading. Let's look at an example:

import { LazyLoadedModule } from './';
// ...
const module = new LazyLoadedModule();

In this example, we performed the pair in the main applicationLazyLoadedModulestatic import. This will cause the build tool toLazyLoadedModuleIncluded in the main application bundle, the effect of Lazy Loading cannot be achieved.

Error 2: Mixed static imports and dynamic imports

In some cases, developers may attempt to mix static and dynamic imports, even if they come from the same library entry point, which can break the effects of Lazy Loading and Tree Shaking (tree shake optimization). Even importing different symbols will result in the entire library entry point being statically included in the build rather than generating a separate code block.

For example, consider the following code:

import { SymbolA } from 'my-library';
import('my-library').then((module) => {
  const symbolB = ;
});

In this example, we first perform theSymbolAstatic import, then loaded asynchronously using dynamic importSymbolB. Although these two symbols come from the same library entry point, their combination causes the entire library entry point to be statically included in the build.

To avoid this problem, we should always use dynamic imports to load the Lazy Loaded code instead of performing static imports in the main application.

Best Practice: Create a standalone entry point for Lazy Loaded code

To avoid the trap of Lazy Loading, the best practice is to create separate entry points for code that you want to delay load. This means packing the code for the Lazy Loaded module or component into a separate bundle so that it will only be loaded if needed.

Let's look at an example, suppose we have a Lazy Loaded moduleLazyModule, we can create a separate entry point for it as follows:

// 
const path = require('path');
 = {
  entry: {
    lazyModule: './src/app/lazy-module/',
  },
  output: {
    path: (__dirname, 'dist'),
    filename: '[name].',
  },
};

In this example, weLazyModuleCreated a standalone Webpack configuration fileand define a separate entry pointlazyModule. This will cause Webpack to generate a name calledseparate code blocks.

Next, we need to update the routing configuration of the Angular application to ensure it is loaded if neededLazyModule. This can be usedloadChildrenThe properties are implemented as follows:

const routes: Routes = [
  // ...
  {
    path: 'lazy',
    loadChildren: () => import('./lazy-module/').then(m => ),
  },
  // ...
];

In this way, we tell the Angular application to navigate to/lazyLoading only when routingLazyModule。

Summarize

Lazy Loading is one of the important ways to improve the performance of Angular applications, but you need to be careful to avoid common errors when implementing them. Avoiding static import of Lazy Loaded code, not mixing static imports with dynamic imports, and creating independent entry points for Lazy Loaded code, is the key to achieving successful Lazy Loading. By following best practices, you can better optimize your Angular application and provide a better user experience.

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