js定义对象

时间:2021-10-03 05:35:04

1.工厂模式

function createPerson(name,age,job){ 
var o = {}; 
o.name = name; 
o.age = age; 
o.job = job; 
o.sayName = function(){ 
alert(this.name); 
}; 
return o; 

var tanya = createPerson("tanya","30","female"); 
var ansel = createPerson("ansel","30","male"); 
tanya.sayName(); 
ansel.sayName();

这里先定义o为一个空的对象,然后为o设置了一堆属性。其实也可以直接给o属性的嘛,所以如果这样写也是ok的。

function createPerson(name,age,job){ 
var o = { 
name : name, 
age : age, 
job : job, 
sayName : function(){ 
alert(this.name); 

}; 
return o; 

var tanya = createPerson("tanya","30","female"); 
var ansel = createPerson("ansel","30","male"); 
tanya.sayName(); 
ansel.sayName();

2.构造函数模式

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

var tanya = new Person("tanya","30","female"); 
var ansel = new Person("ansel","30","male"); 
tanya.sayName(); 
ansel.sayName();

在这个例子中,tanya和ansel都有一个constructor属性,该属性指向person。 
考虑一下如下的情况:

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

Person("tanya","30","female"); 
Person("ansel","30","male"); 
window.sayName(); 
window.sayName();

发现两次弹出的都是ansel,这是因为不用new的话,就不是一个person的实例,而仅仅在执行函数。而在全局作用域调用一个函数时this总是指向Global对象。而Global对象在浏览器中就是window对象。

我们还可以用构造模式在另外一个对象中调用sayName方法,还记得Apply和call么,来吧再考虑另外一种情况,

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

var olivia = {}; 
Person.call(olivia,"tanya","30","female"); 
olivia.sayName(); 
var philip = {} 
Person.apply(philip,["ansel","30","male"]); 
philip.sayName();

原型模式就要考虑原型链了,分析一下,sayName方法在实例中被重复定义了两次,但其实没有必要创造两个一样的副本。使用原型方法,可以使是tanya和ansel的共享一个sayName方法。 
于是原型模式的写法如下:

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

Person.prototype.sayName= function(){ 
alert(this.name); 
}; 
var tanya = new Person("tanya","30","female"); 
var ansel = new Person("ansel","30","male"); 
tanya.sayName(); 
ansel.sayName();