Simple example of inheritance in JavaScript.

js-inheritance.js

function Car (licensePlate) {
  this.licensePlate = licensePlate;
}

Car.prototype.isLegal = function () {
  return !!this.licensePlate;
};

function Mustang (licensePlate) {
  Car.call(this, licensePlate);
}

Mustang.prototype = new Car();

Mustang.prototype.make = 'Ford';

var mustang = new Mustang('bullitt');
console.log(mustang.make); // 'Ford'
console.log(mustang.isLegal()); // true  

var car = new Car();
console.log(car.make); // undefined