Angular Optimizing client application size with lightweight injection tokens
In Angular, injection tokens are used to provide dependencies to components and services. These tokens can be used to configure the application with different values at runtime. By default, Angular uses Type as the token for a dependency, which can lead to a large bundle size if there are many different types of dependencies in the application.
One way to optimize the bundle size of an Angular application is to use lightweight injection tokens instead of Type for dependencies. Lightweight injection tokens are a way to reduce the size of the application by replacing the Type token with a smaller token.
Here’s an example of how to create a lightweight injection token for a dependency:
import { InjectionToken } from '@angular/core';
export const LIGHTWEIGHT_TOKEN = new InjectionToken('lightweight_token');
Once you’ve created the lightweight injection token, you can use it to provide the dependency in the @Inject decorator:
import { Component, Inject } from '@angular/core';
import { LIGHTWEIGHT_TOKEN } from './lightweight-token';
@Component({
selector: 'app-example',
template: `{{value}}`,
})
export class ExampleComponent {
constructor(@Inject(LIGHTWEIGHT_TOKEN) public value: string) {}
}
You can also use the lightweight injection token to provide the dependency in the module’s providers array:
import { NgModule } from '@angular/core';
import { LIGHTWEIGHT_TOKEN } from './lightweight-token';
@NgModule({
providers: [{ provide: LIGHTWEIGHT_TOKEN, useValue: 'lightweight' }],
})
export class AppModule {}
It’s worth mentioning that by using lightweight injection tokens, the token’s name is not included in the final bundle, which can significantly reduce the size of your application. Additionally, it’s also recommended to use the useValue or useExisting instead of useClass or useFactory when providing the dependency in the providers array, which will further reduce the size of your application.
Angular When tokens are retained
In Angular, when a token is retained, it means that the token is not released when it is no longer needed. This can lead to a memory leak, as the token continues to occupy memory even though it is no longer in use.
There are several situations in which tokens can be retained in an Angular application:
Singleton services: When a service is provided as a singleton, it means that the same instance is used throughout the application. If the service holds a reference to a token, the token will be retained until the service is destroyed.
Retained tokens in component constructors: If a component constructor holds a reference to a token, the token will be retained until the component is destroyed.
Retained tokens in observables: If an observable holds a reference to a token, the token will be retained until the observable is unsubscribed.
Retained tokens in subscriptions: If a subscription holds a reference to a token, the token will be retained until the subscription is unsubscribed.
To prevent tokens from being retained, it’s important to ensure that references to tokens are released when they are no longer needed. This can be done by unsubscribing from observables, unsubscribing from subscriptions, and properly destroying components and services.
It’s worth mentioning that Angular’s change detection mechanism can help with preventing retained tokens as well, as it allows the framework to automatically unsubscribe and destroy components that are no longer needed. Additionally, using Angular’s dependency injection mechanism to provide services and tokens can also help to prevent retained tokens.
When to use the lightweight injection token pattern example code
The lightweight injection token pattern is a technique that can be used to reduce the size of an Angular application by replacing the Type token with a smaller token. This pattern can be useful in several scenarios:
1. Large number of dependencies: If your application has a large number of dependencies, using lightweight injection tokens can help to reduce the size of the application by replacing the Type token with a smaller token for each dependency.
2. Large number of components: If your application has a large number of components, each component may have a reference to the Type token for its dependencies, which can lead to a large bundle size. Using lightweight injection tokens can help to reduce the size of the bundle by replacing the Type token with a smaller token for each component.
3. Third-party libraries: If your application uses third-party libraries, they may have a large number of dependencies and components. Using lightweight injection tokens can help to reduce the size of the application by replacing the Type token with a smaller token for each dependency and component in the third-party library.
4. Large applications : In general, for large applications, using lightweight injection tokens can help to reduce the bundle size and improve the application’s performance.
Here’s an example of how to use the lightweight injection token pattern in an Angular application:
import { InjectionToken } from '@angular/core';
export const LIGHTWEIGHT_TOKEN = new InjectionToken('lightweight_token');
@Injectable({
providedIn: 'root',
useValue: 'lightweight'
})
export class Service {
constructor(@Inject(LIGHTWEIGHT_TOKEN) public value: string) {}
}
Angular Using lightweight injection tokens example code
Yes, here is an example of how to use lightweight injection tokens in an Angular application:
1. Create a new injection token for a dependency:
import { InjectionToken } from '@angular/core';
export const LIGHTWEIGHT_TOKEN = new InjectionToken('lightweight_token');
This creates an injection token with the name “lightweight_token” that can be used to provide the dependency.
2. Use the injection token to provide the dependency in a service:
import { Injectable, Inject } from '@angular/core';
import { LIGHTWEIGHT_TOKEN } from './lightweight-token';
@Injectable({
providedIn: 'root',
useValue: 'lightweight'
})
export class Service {
constructor(@Inject(LIGHTWEIGHT_TOKEN) public value: string) {}
}
This service uses the LIGHTWEIGHT_TOKEN to inject the value of ‘lightweight’ into the service.
3. Use the service in a component
import { Component } from '@angular/core';
import { Service } from './service';
@Component({
selector: 'app-example',
template: `{{value}}`,
})
How to use Angular Use the lightweight injection token for API definition example
An example of using a lightweight injection token for an API definition in an Angular application might look like this:
1. Create a new injection token for the API definition:
import { InjectionToken } from '@angular/core';
export const API_URL = new InjectionToken('api_url');
This creates an injection token with the name “api_url” that can be used to provide the API definition.
2. Use the injection token to provide the API definition in the app.module.ts file:
import { NgModule, InjectionToken } from '@angular/core';
import { HttpClientModule } from '@angular/common/http';
import { API_URL } from './api-token';
@NgModule({
imports: [
HttpClientModule
],
providers: [
{ provide: API_URL, useValue: 'https://api.example.com' }
]
})
export class AppModule { }
This configures the application to use the value “https://api.example.com” for the API_URL token.
3. Use the API_URL token in a service to make HTTP requests:
import { Injectable, Inject } from '@angular/core';
import { HttpClient } from '@angular/common/http';
import { API_URL } from './api-token';
@Injectable({
providedIn: 'root'
})
export class ApiService {
constructor(private http: HttpClient, @Inject(API_URL) private apiUrl: string) {}
getData() {
return this.http.get(`${this.apiUrl}/data`);
}
}
In this example, the ApiService uses the API_URL token to construct the URL for making HTTP requests to the API.
This way, you can use the same injection token in any other service or component to make requests to the API, and you can change the URL of the API in a single place, which makes it easier to manage the application.