工厂模式

function createPerson(name, age, job) {
  var o = new Object();
  o.name = name;
  o.age = age;
  o.job = job;
  o.sayName = function () {
    alert(this.name);
  };
  return o;
}
var person1 = createPerson("Nicholas", 29, "Software Engineer");
var person2 = createPerson("Greg", 27, "Doctor");

优点：避免创建多个对象时的重复代码问题

缺点：无法解决对象识别问题（不知道一个对象的类型）

构造函数模式

function Person(name, age, job) {
  this.name = name;
  this.age = age;
  this.job = job;
  this.sayName = function () {
    alert(this.name);
  }
}

var person1 = new Person("Nicholas", 29, "Software Engineer");
var person2 = new Person("Greg", 27, "Doctor");

alert(person1.constructor == Person); // true
alert(person1 instanceof Person); // true

构造函数可以当作普通函数一样使用，例如不使用new关键字：

Person("Greg", 27, "Doctor");// 添加到window
window.sayName(); // "Greg"

也可以在另一个对象作用域中使用：

var o = new Object();// 在另一个对象的作用域中调用
Person.call(o, "Kristen", 25, "Nurse");
o.sayName();

缺点：每个方法都会在实例上被创建一遍，sayName()是Function的实例，因此person1的sayName和person2的sayName不是同一个对象。解决方法是把sayName()放在外面，但是破坏了封装性。

function Person(name, age, job) {
  this.name = name;
  this.age = age;
  this.job = job;
  this.sayName = sayName;
}

function sayName() {
  alert(this.name);
}

var person1 = new Person("Nicholas", 29, "Software Engineer");
var person2 = new Person("Greg", 27, "Doctor");

alert(person1.constructor == Person);
alert(person1 instanceof Person);
alert(person1.sayName === person2.sayName);// true

原型模式

function Person() {

}

Person.prototype.name = "Nicholas";
Person.prototype.age = 29;
Person.prototype.job = "Software Engineer";
Person.prototype.sayName = function () {
  alert(this.name);
}

var person1 = new Person();
person1.sayName();

var person2 = new Person();
person2.sayName();

alert(person1.sayName === person2.sayName);// true