Analysis of the initialization technology instance of lazy loading module in Angular

Introduction

Angular is a powerful front-end development framework that provides many features to optimize application performance and user experience. One of the key features is the support of Lazy Loaded Modules, which allows applications to be divided into small modules and loaded on demand, thereby reducing initial loading time and resource usage. In this article, we will explore the initialization process of lazy loading modules in detail, focusing on theMODULE_INITIALIZERandAPP_INITIALIZERThe difference and how to use them.

First know about module initialization in Angular

In Angular applications, modules are the basic unit of code organization, and lazy loading modules is an advanced module concept. Usually, the initialization of the Angular application is inAPP_INITIALIZERCompleted in. This is a function that executes some initialization logic when the application starts. However,APP_INITIALIZERAn important feature of this is that it completes initialization before lazy loading, which can cause some problems.

Imagine you have a lazy loading module that contains initialization logic that needs to be run when the module is loading. becauseAPP_INITIALIZERRunning before lazy loading, these initialization logics will be forced to run during the main module initialization, rather than when the lazy loading module is loaded, which can lead to unnecessary performance problems.

Introduce MODULE_INITIALIZER

To solve this problem, Angular introducedMODULE_INITIALIZER. This is an injection token that allows you to provide an initialization function that runs before the lazy loading module is loaded. useMODULE_INITIALIZER, you can control the initialization process of the module with more precise accuracy.

Here's how to use itMODULE_INITIALIZERExample:

import { InjectionToken, NgModule, Injector } from '@angular/core';
export const MODULE_INITIALIZER = new InjectionToken<() => Promise<void>>('MODULE_INITIALIZER');
export function initializeApp(injector: Injector): () => Promise<void> {
  return () => {
    // Execute your initialization logic here    return ();
  };
}
@NgModule({
  providers: [
    {
      provide: MODULE_INITIALIZER,
      useFactory: initializeApp,
      deps: [Injector],
      multi: true,
    },
  ],
})
export class MyLazyLoadedModule {}

In the example above, we first create aMODULE_INITIALIZERInjection token, and then define a name calledinitializeAppinitialization function. This function will be run before the module is loaded. Finally, we use it in the module's provider arrayMODULE_INITIALIZER,WillinitializeAppFunctions are registered as initialization logic.

Combination of MODULE_INITIALIZER and lazy loading

MODULE_INITIALIZERWhat's really powerful is its close integration with lazy loading. When you define a module as lazy loading, Angular automatically recognizes theMODULE_INITIALIZER, and execute it before the module loads.

Let's look at a more specific example, suppose we have an e-commerce application with a lazy loading shopping cart module. We want to perform some initialization logic when the user first opens the cart, such as getting a list of items in the cart. Here's how to do it:

import { InjectionToken, NgModule, Injector } from '@angular/core';
export const MODULE_INITIALIZER = new InjectionToken<() => Promise<void>>('MODULE_INITIALIZER');
export function initializeCart(injector: Injector): () => Promise<void> {
  return () => {
    const cartService = (CartService);
    return (); // Get the shopping cart product list before loading the shopping cart module  };
}
@NgModule({
  providers: [
    {
      provide: MODULE_INITIALIZER,
      useFactory: initializeCart,
      deps: [Injector],
      multi: true,
    },
  ],
})
export class CartModule {}

In the example above, weCartModuleDefine aMODULE_INITIALIZER, it gets the shopping cart item list before loading the shopping cart module. This ensures that the initialization logic is performed only when the user accesses the cart.

Summarize

In this article, we have studied the lazy loading module initialization technology in Angular and paid special attention to itMODULE_INITIALIZERUse of By usingMODULE_INITIALIZER, you can control the initialization process of lazy loading modules more accurately, ensuring that the initialization logic runs when the module is loaded, rather than when the application is started. This is very helpful for improving application performance and user experience.

With practical examples, we show how to useMODULE_INITIALIZERto execute the initialization logic of lazy loading modules and how to run specific code in it. This will help you better understand and leverage lazy loading module initialization techniques in Angular to build more efficient front-end applications.

Remember to consider using Angular applicationsMODULE_INITIALIZERTo optimize the initialization of lazy load modules to provide better user experience and performance.

The above is the detailed analysis of the initialization technology example of the lazy load module in Angular. For more information about the initialization of Angular lazy load, please pay attention to my other related articles!