Angular2 multiple constructor implementations are not allowed TS2392

Question

How can I get around using multiple constructors within a component? Currently I am getting the error:

'Multiple constructor implementations are not allowed'.

questions: any[];
constructor( service: QuestionSignupStepOneService ) { 
    this.questions = service.getQuestions(); 
}
constructor( service: QuestionSignupStepOneAService ) { 
    this.questions = service.getQuestions(); 
}

Is there anyway to simplify what I am trying to do? The code compiles properly but will only run through the first service, ignoring the second.

Edit in 2021: I realized long ago that this was a silly question, but I'm leaving this up because if I did not understand constructors enough so to ask the question then other might find themselves here as well

Answer 1

Making multiple constructors with the same parameters doesn't make sense unless they have different types, in Typescript you can do the following:

class Foo {
  questions: any[];
  constructor(service: QuestionSignupStepOneService, param2?: Param2Type) { 

    this.questions = service.getQuestions(); 
    if(param2){
        console.log(param2);
    }
  }
}

This is equal to two constructors, the first one is new Foo(service) and the second one is new Foo(service, param2).

Use ? to state that the parameter is optional.

If you want two constructors with the same parameter but for different types you can use this:

class Foo {
  questions: any[];
  constructor(service: QuestionSignupStepOneService | QuestionSignupStepOneAService) {

    if(service instanceof QuestionSignupStepOneService){
       this.questions = service.getQuestions(); 
    }
    else {
       this.questions = service.getDifferentQuestions(); 
    }
  }
}