How to make a class that returns an instance without `new` keyword

Question

I would like to create a class that would work like, for example, the built-in BigInt. So I can do:

BigInt('111')
BigInt('222').toString()

Please guide me on how to code it. I'm using NodeJS with vanilla JavaScript. Thank you so much in advance.

Answer 1

There are several solutions.

It's probably easiest to create a normal class and then a helper function that creates the object.

class MyRealClass {
  constructor(name) {
    this.name = name;
  }
  hello() {
    console.log('Hello', this.name);
  }
}

function creteMyRealClass(name) {
  if (new.target) throw Error("Object should not be called with 'new'");
  return new MyRealClass(name);
}


creteMyRealClass('Alpha').hello();

Another option is to use a helper function that calls Object.create

// By declaring an external object with attributes
// common to all objects of this type, you save memory
// and execution time
const MyPrototype = {
  hello() {
    console.log('Hello', this.name);
  },
};

function createMyPrototype(name) {
  if (new.target) throw Error("Object should not be called with 'new'");
  const obj = Object.create(MyPrototype);
  obj.name = name;
  return obj;
}

const b = createMyPrototype('Beta');
b.hello();