TypeScript Constructor Overload with Empty Constructor

user_2854890 0
Viewed 69086

Why is it not allowed to have separate constructor definitions in TypeScript?
To have e.g. two constructors, I need to write my code like this. 

constructor(id: number)
constructor(id: number, name?: string, surname?: string, email?: string) {
    this.id = id;
    this.name = name;
    this.surname = surname;
    this.email = email;
}

Thereby I need to put ? after the parameters that are not required in the first constructor.

Why can't I write it like this?

constructor(id: number) {
    this.id = id;
}

constructor(id: number, name: string, surname: string, email: string) {
    this.id = id;
    this.name = name;
    this.surname = surname;
    this.email = email;
}

So that for both constructors all parameters are mandatory.

Moreover, if I need to have an empty constructor things get even weirder, since I need to mark every parameter with a ?.

constructor()
constructor(id?: number, name?: string, surname?: string, email?: string) {
    this.id = id;
    this.name = name;
    this.surname = surname;
    this.email = email;
}

Why does TypeScript differs from common languages like C# or Python here?

I would expect it to work like this.

constructor() {

}
constructor(id: number, name: string, surname: string, email: string) {
    this.id = id;
    this.name = name;
    this.surname = surname;
    this.email = email;
}

So you can pass none parameter or must pass all parameters.

typescript constructor
4 Answers

You can use Builder pattern to solve this. Even in C# or Python, it quickly becomes a better approach as the number of constructor arguments grows.

class Foo {
  constructor(public id: number, public name: string, public surname: string, public email: string) {
  }
  static Builder = class {
    id: number = NaN;
    name: string = null;
    surname: string = null;
    email: string = null;
    Builder() {
    }
    build(): Foo {
      return new Foo(this.id, this.name, this.surname, this.email);
    }
  }
}
user_5336440
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