JS: Define a Class Without Using Keyword class

This page shows you how to define a class without using the keyword class 〔see Class〕 , and then another version without using any keywords class, new, this.

Suppose we want to define a class CC, with a constructor CC(x) that adds a property key kk with value x, and one prototype method ff, and one static method ss.

Here's a typical way by using the keyword class.

Using Keyword class

// Using Keyword class

class CC {
  constructor(x) {
    this.kk = x;
  }

  static ss(x) {
    return "ss " + x.toString();
  }

  ff(x) {
    return "ff " + x.toString();
  }
}

// --------------------------------------------------

console.log(CC.ss(3) === "ss 3");

const jj = new CC(4);

console.log(jj.hasOwnProperty("kk"));
console.log(jj.kk === 4);

console.log(jj.ff(2) === "ff 2");

console.log(Reflect.getPrototypeOf(jj) === CC.prototype);
console.log(jj.constructor === CC);

Without Keyword class

function CC(x) {
  this.kk = x;
}

CC.ss = function (x) {
  return "ss " + x.toString();
};

CC.prototype.ff = function (x) {
  return "ff " + x.toString();
};

// --------------------------------------------------

console.log(CC.ss(3) === "ss 3");

const jj = new CC(4);

console.log(jj.hasOwnProperty("kk"));
console.log(jj.kk === 4);

console.log(jj.ff(2) === "ff 2");

console.log(Reflect.getPrototypeOf(jj) === CC.prototype);
console.log(jj.constructor === CC);

Without Keywords class, new, this

This makes it easier to see what class is doing, because all parent child relationship are explicit. Here's the code:

const CC = ((x) => {
  const xthis = {};
  Reflect.setPrototypeOf(xthis, CC.prototype);

  xthis.kk = x;

  return xthis;
});

CC.ss = function (x) {
  return "ss " + x.toString();
};

CC.prototype = {
  ff: function (x) {
    return "ff " + x.toString();
  },
  constructor: CC,
};

// --------------------------------------------------

console.log(CC.ss(3) === "ss 3");

const jj = CC(4);

console.log(jj.hasOwnProperty("kk"));
console.log(jj.kk === 4);

console.log(jj.ff(2) === "ff 2");

console.log(Reflect.getPrototypeOf(jj) === CC.prototype);
console.log(jj.constructor === CC);

Without Keywords class, new, this, function

const CC = ((x) => {
  const xthis = {};
  Reflect.setPrototypeOf(xthis, CC.prototype);

  xthis.kk = x;

  return xthis;
});

CC.ss = (x) => {
  return "ss " + x.toString();
};

CC.prototype = {
  ff: ((x) => {
    return "ff " + x.toString();
  }),
  constructor: CC,
};

// --------------------------------------------------

console.log(CC.ss(3) === "ss 3");

const jj = CC(4);

console.log(jj.hasOwnProperty("kk"));
console.log(jj.kk === 4);

console.log(jj.ff(2) === "ff 2");

console.log(Reflect.getPrototypeOf(jj) === CC.prototype);
console.log(jj.constructor === CC);