Question 352104 in Javascript Question posted in
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Javascript – How to make a class that returns an instance without `new` keyword

I would like to create a class that would work like for example 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.

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2

Answers


  1. 0

    To achieve something like this, you will have to use factory functions instead of the usual class constructors. Here is an example:

    function MyBigInt(value) {
    return {
      toString: function() {
        return `My Value: '${value}'`;
      }
    };
  }
  
console.log(MyBigInt('111').toString()); 
// Output: My Value: '111'
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  2. 0

    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();
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