Constructor overload in TypeScript

Question

Has anybody done constructor overloading in TypeScript. On page 64 of the language specification (v 0.8), there are statements describing constructor overloads, but there wa

Answer 1

Regarding constructor overloads one good alternative would be to implement the additional overloads as static factory methods. I think its more readable and simple than checking for all possible argument combinations at the constructor. Here is a simple example:

function calculateAge(birthday): number {
  return new Date().getFullYear() - birthday;
}

class Person {
  static fromData(data: PersonData): Person {
    const { first, last, birthday, gender = 'M' } = data;
    return new this(
      `${last}, ${first}`,
      calculateAge(birthday),
      gender,
    );
  }

  constructor(
    public fullName: string,
    public age: number,
    public gender: 'M' | 'F',
  ) {}

  toString(): string {
    return `Hello, my name is ${this.fullName} and I'm a ${this.age}yo ${this.gender}`;
  }
}

interface PersonData {
  first: string;
  last: string;
  birthday: string;
  gender?: 'M' | 'F';
}


const personA = new Person('Doe, John', 31, 'M');
console.log(personA.toString());
const personB = Person.fromData({
  first: 'Jane',
  last: 'Smith',
  birthday: '1986',
  gender: 'F',
});
console.log(personB.toString());

---

Method overloading in TypeScript isn't for real, let's say, as it would require too much compiler-generated code and the core team try to avoid that at all costs. Currently the main reason for method overloading to be present on the language is to provide a way to write declarations for libraries with magic arguments in their API. Since you'll need to do all the heavy-lifting by yourself to handle different sets of arguments I don't see much advantage in using overloads instead of separated methods.