InjectionToken
Creates a token that can be used in a DI Provider.
class InjectionToken<T> {
constructor(_desc: string, options?: { providedIn?: Type<any> | "root"; factory: () => T; })
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
parameterized 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.
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
Properties
Property | Description |
---|---|
ngInjectableDef: never | undefined
|
Read-only. |
protected _desc: string
|
Declared in constructor. |
Methods
ParametersThere are no parameters. Returns
|
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');
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();