StyleGuide - In TypeScript dependency injection

[mgechev]

To be discussed.

// cc @johnpapa @wardbell

---

• Use the @Injectable() decorator instead of explicitly declaring the dependencies using @Inject(TOKEN).

  Why?: Using @Injectable() the TypeScript compiler will emit the required type metadata, which makes the code using @Inject() unnecessary verbose and less readable.

[mgechev]

This style should be more explicit because some of the DI tokens are not types and need to be declared with @Inject.

[zoechi]

If you use @Inject(SomeType) does it need the @Injectable() decorator as well if it has constructor parameters?

[mgechev]

No, it doesn't. If you have SomeType1 and SomeType2 it is better to use @Injectable on top of the class instead of applying two times the parameter injector @Inject over the two constructor parameters, i.e.:

// avoid
class Bar {
  constructor(@Inject(Foo) foo: Foo, @Inject(Baz) baz: Baz) {
    //...
  }
}

// recommended
@Injectable()
class Bar {
  constructor(foo: Foo, baz: Baz) {
    //...
  }
}

[johnpapa]

@mgechev Want to take a stab at writing this one up? I think we should ad something on this, this week. Thanks!

[johnpapa]

we added this. closed with #1170

those i cant seem to close :) @wardbell some help please?