How to Pass Parameters Rendered from Backend to Angular2 Bootstrap Method

In Angular2, the bootstrap method initiates the application and accepts a component along with an optional array of providers. This article explores how to pass parameters obtained from the backend to the bootstrap method.

Using Angular's Dependency Injection

A straightforward solution involves using Angular's dependency injection:

import { bootstrap } from '@angular/platform-browser-dynamic';
import { AppComponent } from "./app.component.ts";

// Retrieve headers from the server
var headers = ...;

// Pass headers to bootstrap method using dependency injection
bootstrap(AppComponent, [{provide: 'headers', useValue: headers}]);

Within the component or service that needs the headers, you can inject them using the @Inject decorator:

class SomeComponentOrService {
   constructor(@Inject('headers') private headers) {}
}

Using a Custom RequestOptions Provider

Alternatively, you can create a custom BaseRequestOptions provider:

class MyRequestOptions extends BaseRequestOptions {
  constructor (private headers) {
    super();
  }
} 

// Retrieve header values from the server
var values = ...;
var headers = new MyRequestOptions(values);

// Pass the custom request options to the bootstrap method
bootstrap(AppComponent, [{provide: BaseRequestOptions, useValue: headers}]);

This method allows you to directly provide the modified request options to the bootstrap method, which can be useful if you need more control over the request configuration.

Utilizing APP_INITIALIZER

In recent versions of Angular (RC.5 and later), you can use the APP_INITIALIZER token to execute a function that initializes the context and waits for it to resolve before the app bootstraps.

function loadContext(context: ContextService) {
  return () => context.load();
}

@NgModule({
  ...
  providers: [ ..., ContextService, { provide: APP_INITIALIZER, useFactory: loadContext, deps: [ContextService], multi: true } ],
})

This approach provides a centralized way to initialize the context and delay the application startup until the required data is available.

Conclusion

By leveraging these techniques, you can pass parameters rendered from the backend to the Angular2 bootstrap method, enabling you to inject these parameters into components and services during the application's initialization phase.

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