Callable & Newable Objects in JavaScript: Full Example

      'use strict';

const ogp = Object.getPrototypeOf;
const ohp = Object.prototype.hasOwnProperty;

/**
 * Base constructor that returns a self-referential
 * callable/newable function.
 */
const Cstr = function () {
  const root = this;
  const main = this.constructor;
  const isItSelf = main === Cstr;

  const Self = function () {
    if (new.target) {
      const isSelfInside = this.constructor === Self;
      const isCstrInside = this.constructor === Cstr;

      if (!isSelfInside && !isCstrInside) {
        Object.setPrototypeOf(ogp(this), root);
        return Cstr.call(this);
      }

      const Constructor = isItSelf ? Cstr : main;
      return new Constructor();
    }
    return Self;
  };

  Object.setPrototypeOf(Self, root);
  Self.prototype.constructor = root;
  Self.value++;
  return Self;
};

Object.setPrototypeOf(Cstr.prototype, Cstr);
Cstr.prototype.value = 0;

/* ---------------- DEMO ---------------- */

console.log('\n=== basic construction ===');
const item = new Cstr();
console.log('item instanceof Cstr:', item instanceof Cstr);
console.log('item instanceof Function:', item instanceof Function);
console.log('item.value:', item.value);

new item; // works
item();   // works

console.log('\n=== class extension ===');
class ExtendedCstr extends Cstr {}
const entity = new ExtendedCstr();
console.log('entity instanceof ExtendedCstr:', entity instanceof ExtendedCstr);
console.log('entity instanceof Cstr:', entity instanceof Cstr);
new entity; // works
entity();   // works

console.log('\n=== deep extension & sequencing ===');
class ExtendedExtendedCstr extends ExtendedCstr {
  constructor() {
    super();
  }
}
const exEx = new ExtendedExtendedCstr();
exEx();           // callable
const exEx2 = new exEx(); // newable

class ItemExtendedCstr extends exEx2.constructor {
  constructor() {
    super();
  }
}
const itemItem = new ItemExtendedCstr();
itemItem();                   // callable
const postItemItem = new itemItem(); // newable

console.log('\n=== checks ===');
console.log('itemItem instanceof ItemExtendedCstr:', itemItem instanceof ItemExtendedCstr);
console.log('postItemItem instanceof ItemExtendedCstr:', postItemItem instanceof ItemExtendedCstr);
console.log('postItemItem.value:', postItemItem.value);
console.log('has own "value" on postItemItem:', ohp.call(postItemItem, 'value'));
console.log('proto(value):', ogp(postItemItem).value);
console.log('proto^2(value):', ogp(ogp(postItemItem)).value);