 
function Sandy(val){ 
var value = val; 
this.getValue = function(){ 
return value; 
}; 
this.setValue = function(val){ 
value = val; 
}; 
} 
//usage 
var sandy = new Sandy("test"); 
sandy.value 
// => undefined 
sandy.setValue("test2") 
sandy.getValue 

下面是JavaScript權(quán)威指南（中文第五版）中P152頁使用閉包的一個(gè)例子.

復(fù)制代碼代碼如下:

 
function makeProperty(o, name, predicate) { 
var value; //This is property value; 

//The setter method simply returns the value 
o['get' + name] = function() { return value;}; 

//The getter method stores the value or throws an exception if 
//the predicate rejects the value 
o['set' + name] = function(v) { 
if (predicate && !predicate(v) { 
throw 'set' + name + ': invalid value ' + v; 
} else { 
value = y; 
} 
} 
} 

//The following code demenstrates the makeProperty() method 
var o = {}; // Here is an empty object 

//Add property accessor methods getName and setName 
//Ensure that only string values are allowed 
makeProperty(o, 'Name', function(x) { return typeof x == 'string'; }); 

o.setName('Frank'); 　　//Set the property value; 
print(o.getName()); 　　//Get the property value 
o.setName(0); //Try to set a value of the wrong type 

第二種方法是使用__defineSetter__與__defineGetter__來實(shí)現(xiàn)accessor,看下劃線就知道它們并非標(biāo)準(zhǔn),適用于Firefox 2.0+, Safari 3.0+, Google Chrome 1.0+ 和 Opera 9.5+ ,方法使用見MDN.

復(fù)制代碼代碼如下:

 
function Sandy(val){ 
var value = val, 
_watch = function(newVal) { 
console.log('val is Changed to : ' + newVal); 
} 

this.__defineGetter__("value", function(){ 
return value; 
}); 

this.__defineSetter__("value", function(val){ 
value = val; 
_watch(val); 
}); 
} 

var sandy = new Sandy("test"); 
sandy.value 
// => test 
sandy.value = "test2"; 
// => 'val is Changed to : test2' 
sandy.value 
// => "test2" 

　除了__defineG/Setter__外, 你還可以使用'set'、'get'關(guān)鍵字在在原型對(duì)象上定義accessor,對(duì)于單個(gè)對(duì)象同樣適用, 適用于Firefox 2.0+, Safari 3.0+, Google Chrome 1.0+ 和 Opera 9.5+.

復(fù)制代碼代碼如下:

 
function Sandy(val){ 
this.value = val; 
} 

Sandy.prototype = { 
get value(){ 
return this._value; 
}, 
set value(val){ 
this._value = val; 
} 
}; 

//Or 

var sandy = { 
'_value' : 'sandy', 
get value() { 
　　return this._value; 
}, 
set value(val) { 
　　this._value = val; 
} 
} 

最后一種方法,用到了Object的靜態(tài)方法defineProperty,作用于單個(gè)對(duì)象,該方法應(yīng)該屬于ES5的范疇了,目前似乎只有Chrome 支持這種方法，其實(shí)Ie8也支持,但操作對(duì)象僅限于Dom節(jié)點(diǎn)(Dom node),見IEBlog,該方法的使用見MDN.

復(fù)制代碼代碼如下:

 
var sandy = {}, rValue; 
Object.defineProperty(sandy, 'value' , 
{ 
'set' : function(val) { 
rValue = val; 
}, 
'get' : function() { 
return rValue; 
}, 
'enumerable' : true, 
'configurable' : true 
} 
) 
//Ie8+ 
Object.defineProperty(document.body, "description", { 
get : function () { 
return this.desc; 
}, 
set : function (val) { 
this.desc = val; 
} 
}); 
document.body.description = "Content container"; 
// document.body.description will now return "Content container" 