Can some explain this Injection token syntax

Question

I was looking at the angular 2 validator file . Can someone explain the syntax after "new InjectionToken"? I know its a generic type but how do you understand it?

new InjectionToken<Array<Validator|Function>>('NgValidators');

Answer 1

Your token can take the following type

Array<Validator|Function>

it means array of Validator or Function

where Validator is a class that implements Validator interface:

export interface Validator {
  validate(c: AbstractControl): ValidationErrors|null;
  registerOnValidatorChange?(fn: () => void): void;
}

InjectionToken gives you type checking benefit when getting a dependency through injector instance

See also

• Angular 2 OpaqueToken vs Angular 4 InjectionToken