1、构造函数（相对于面向对象编程语言里面的类）
2、对象实例（它是由构造函数构造出来的对象，使用到关键字 new）
3、this关键字（往往是指我们的对象本身）
下面我们来看一个实例：
var Person = function Person(living, age, gender) {
// "this" below is the new object that is being created (i.e. this = new Object();)
this.living = living;
this.age = age;
this.gender = gender;
this.getGender = function() {return this.gender;};
}
// when the function is called with the new keyword "this" is returned instead of false
// instantiate a Person object named cody
var cody = new Person(true, 33, 'male');
// cody is an object and an instance of Person()
console.log(typeof cody); // logs object
console.log(cody); // logs the internal properties and values of cody
console.log(cody.constructor); // logs the Person() function