Implementing the "new" operator in JavaScript

gistfile1.js

// New is a function that takes a function F
function New (F) {
   var o = {}; // and creates a new object o
   o.__proto__ = F.prototype // and sets o.__proto__ to be F's prototype
   
   // New returns a function that...
   return function () {
     F.apply(o, arguments); // runs F with o as "this", passing along any arguments
     return o; // and returns o, the new object we created
   }
}


// Example usage
function Student (name) {
  this.name = name
}
Student.prototype.greet = function () {
  console.log("Hi, ", this.name);
}

var nick = New (Student)("Nick");
// var nick = (New(Student))("Nick");  // the same! 
nick.name; // "Nick"
nick.greet(); // prints "Hi, Nick"

// Compare with:
var dave = new Student("Dave");
dave.name; // "Dave"
dave.greet(); // prints "Hi, Dave"