In Angular 8, you can execute code before the application boots up using the APP_INITIALIZER
token and the APP_INITIALIZER
provider. This allows you to run some initialization code before the Angular application starts.
Here’s an example of how you can call a function before the Angular application boots up:
- Create a Function
Create a function that performs the initialization task you want to execute before the Angular app starts. For instance:
import { Injectable } from '@angular/core';
@Injectable({
providedIn: 'root'
})
export class MyInitializationService {
constructor() {}
initializeApp(): Promise<any> {
// Perform initialization tasks here
return new Promise((resolve, reject) => {
// Simulating asynchronous task, you can replace this with your logic
setTimeout(() => {
console.log('Initialization task completed');
resolve();
}, 2000); // Simulating a delay of 2 seconds
});
}
}
- Use
APP_INITIALIZER
in AppModule
Open yourapp.module.ts
file and provide the function you want to execute before bootstrap usingAPP_INITIALIZER
:
import { NgModule, APP_INITIALIZER } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { MyInitializationService } from './my-initialization.service';
// ... other imports and declarations
export function initializeApp(myInitializationService: MyInitializationService) {
return () => myInitializationService.initializeApp();
}
@NgModule({
declarations: [/* ... */],
imports: [BrowserModule],
providers: [
MyInitializationService,
{
provide: APP_INITIALIZER,
useFactory: initializeApp,
deps: [MyInitializationService],
multi: true
}
],
bootstrap: [/* ... */]
})
export class AppModule { }
In this example, MyInitializationService
is an Injectable service that contains the initializeApp()
method which performs the initialization tasks. Then, in the AppModule
, APP_INITIALIZER
is used to call this initialization function before the Angular app starts.
Remember to replace the initialization logic inside initializeApp()
with your actual initialization tasks.
This setup ensures that your function (initializeApp()
in this case) runs before the application bootstraps, allowing you to perform any required setup or tasks.