Javascript HowItWorks: new, instanceOf etc implementations

implementations.js

// This will return an instance of the classConstructor, which is equalent to
// what we create using new keyword.
function _new (classConstructor, ...args) {
  var obj = Object.create(classConstructor.prototype);
  classConstructor.call(obj, ...args);
  return obj;
}

// alternative to instanceOf
function _instanceOf (object, classConstructor) {
  if (object === null) return false
  if (object.__proto__ === classConstructor.prototype) return true
  else return _instanceOf(object.__proto__, classConstructor) // check in the object's proto chain.
}

// alternative to Object.create
function _objectCreate (object) {
  var obj = {
    __proto__: object
  }
  return obj
}

test_new.js

function test_new () {
  function TestClass (name, location) {
    this._name = name;
    this._location = location;
    this.getName = function () { return this._name; }
  }

  TestClass.prototype.getLocation = function () { return this._location; }
  TestClass.prototype.setName = function (newName) { this._name = newName; }

  const a = new TestClass('anil', 'hyderabad');
  const b = _new(TestClass, 'anil', 'hyderabad');

  const assert = console.assert
  assert(a instanceof TestClass)
  assert(b instanceof TestClass)
  assert(a.constructor.name === 'TestClass');
  assert(b.constructor.name === 'TestClass');
  assert(a.getName() === b.getName());
  assert(a.getLocation() === b.getLocation());
  a.setName('kumar');
  b.setName('kumar');
  assert(a.getName() === b.getName());
}
test_new()