This is the archived documentation for Angular v6. Please visit angular.io to see documentation for the current version of Angular.
API > @angular/core

InjectionToken

Creates a token that can be used in a DI Provider.

See more...

      
      class InjectionToken<T> {
  constructor(_desc: string, options?: {...})
  ngInjectableDef: never | undefined
  protected _desc: string
  toString(): string
}

Description

Use an InjectionToken whenever the type you are injecting is not reified (does not have a runtime representation) such as when injecting an interface, callable type, array or parametrized type.

InjectionToken is parameterized on T which is the type of object which will be returned by the Injector. This provides additional level of type safety.

interface MyInterface {...} var myInterface = injector.get(new InjectionToken<MyInterface>('SomeToken')); // myInterface is inferred to be MyInterface. 
      
      interface MyInterface {...}
var myInterface = injector.get(new InjectionToken<MyInterface>('SomeToken'));
// myInterface is inferred to be MyInterface.

When creating an InjectionToken, you can optionally specify a factory function which returns (possibly by creating) a default value of the parameterized type T. This sets up the InjectionToken using this factory as a provider as if it was defined explicitly in the application's root injector. If the factory function, which takes zero arguments, needs to inject dependencies, it can do so using the inject function. See below for an example.

Additionally, if a factory is specified you can also specify the providedIn option, which overrides the above behavior and marks the token as belonging to a particular @NgModule. As mentioned above, 'root' is the default value for providedIn.

Constructor

constructor(_desc: string, options?: { providedIn?: Type<any> | 'root' | null; factory: () => T; })
      
      constructor(_desc: string, options?: {
    providedIn?: Type<any> | 'root' | null;
    factory: () => T;
})

Parameters

_desc

Type: string.
options

Type: { providedIn?: Type | 'root' | null; factory: () => T; }.

Optional. Default is undefined.

Properties

Property Description
ngInjectableDef: never | undefined Read-only.
protected _desc: string Declared in constructor.

Methods

toString()

toString(): string
      
      toString(): string

Parameters

There are no parameters.

Returns

string

Usage notes

Basic Example

Plain InjectionToken

const BASE_URL = new InjectionToken<string>('BaseUrl'); const injector = Injector.create({providers: [{provide: BASE_URL, useValue: 'http://localhost'}]}); const url = injector.get(BASE_URL); // here `url` is inferred to be `string` because `BASE_URL` is `InjectionToken<string>`. expect(url).toBe('http://localhost'); 
      
      const BASE_URL = new InjectionToken<string>('BaseUrl');
const injector =
    Injector.create({providers: [{provide: BASE_URL, useValue: 'http://localhost'}]});
const url = injector.get(BASE_URL);
// here `url` is inferred to be `string` because `BASE_URL` is `InjectionToken<string>`.
expect(url).toBe('http://localhost');

Tree-shakable InjectionToken

class MyService { constructor(readonly myDep: MyDep) {} } const MY_SERVICE_TOKEN = new InjectionToken<MyService>('Manually constructed MyService', { providedIn: 'root', factory: () => new MyService(inject(MyDep)), }); const instance = injector.get(MY_SERVICE_TOKEN); expect(instance instanceof MyService).toBeTruthy(); expect(instance.myDep instanceof MyDep).toBeTruthy(); 
      
      
  1. class MyService {
  2.   constructor(readonly myDep: MyDep) {}
  3. }
  4.  
  5. const MY_SERVICE_TOKEN = new InjectionToken<MyService>('Manually constructed MyService', {
  6.   providedIn: 'root',
  7.   factory: () => new MyService(inject(MyDep)),
  8. });
  9.  
  10. const instance = injector.get(MY_SERVICE_TOKEN);
  11. expect(instance instanceof MyService).toBeTruthy();
  12. expect(instance.myDep instanceof MyDep).toBeTruthy();