Docs4dev
Docs
angular / 5 / api / core / optional.html

Optional

decorator stable

npm Package @angular/core
Module import { Optional } from '@angular/core';
Source core/src/di/metadata.ts

A parameter metadata that marks a dependency as optional. Injector provides null if the dependency is not found.

How To Use

@Injectable()
class Car {
  constructor(@Optional() public engine:Engine) {}
}

Description

For more details, see the "Dependency Injection Guide".

Example

class Engine {}

@Injectable()
class Car {
  constructor(@Optional() public engine: Engine) {}
}

const injector = ReflectiveInjector.resolveAndCreate([Car]);
expect(injector.get(Car).engine).toBeNull();

© 2010–2018 Google, Inc.
Licensed under the Creative Commons Attribution License 4.0.
https://v5.angular.io/api/core/Optional