为何下面会是相等的

wtcsy 2010-02-09 11:00:02

var  vvv = "1";

function cc(){

	var vv = "1"; 

	function xx(){

		

	}

	alert(xx.__parent__);

	alert(xx.__parent__ === cc.__parent__);

}

alert(cc.__parent__);

cc();

第一个弹出来的是window 这个好理解 cc是全局的作用域在window下
但是第2个xx 还是winow, xx的作用域不是在cc里面了吗为何window alert(xx.__parent__ === cc.__parent__);为 true

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wtcsy 2010-02-09

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引用 6 楼 azraeln 的回复:

因为 "undefined" === "undefined"

请用firefox测试
ie下无法访问__parent__属性...........

nobody@noone 2010-02-09

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因为 "undefined" === "undefined"

wtcsy 2010-02-09

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var  vvv = "1";

(function(){

	alert(this===window)  //true

	function cc(){

		var vv = "1";

		function xx(){

			alert(xx.__parent__ === cc.__parent__);

		}

	}

	alert(cc.__parent__);  //null

})();

wtcsy 2010-02-09

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不对噢
this只是指向他的对象与定义作用域无关吧

sohighthesky 2010-02-09

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var  vvv = "1";

function cc(){

    var vv = "1"; 

    function xx(){

        

    }

alert(this==window)

    alert(xx.__parent__);

    alert(xx.__parent__ === cc.__parent__);

}

alert(this==window)

alert(cc.__parent__);

cc();

wtcsy 2010-02-09

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你这是什么意思?

回复内容太短了！回复内容太短了！回复内容太短了！回复内容太短了！回复内容太短了！回复内容太短了！

xiaojing7 2010-02-09

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 this.xx=function(){

        

    }

wtcsy 2010-02-09

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恩有道理..............

dh20156 2010-02-09

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就是FF下的__parent__不能在嵌套函数中正确的执行，你问为什么那里不是返回null，那我也想知道，你为什么认为那里应该返回null。

在FF下测试的前提已经不对了，所以，不需要继续问这个问题了，你自己知道那里的scope object是什么就可以了，如果一定要测试，可以按#14楼的方法，到Rhino下去测试。

wtcsy 2010-02-09

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这个看的不是很懂
但你想表达的意思是说 firefox下调用函数的__parent__属性总是返回window or null
那为什么
var vvv = "1";
function cc(){
var vv = "1";
function xx(){

}
alert(xx.__parent__); //这里不是返回的 null了.........
alert(xx.__parent__ === cc.__parent__);
}
alert(cc.__parent__);
cc();

浴火_凤凰 2010-02-09

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只是听说过变量有局部作用域，还没有听说函数有局部作用域？是不是这个原因呢？

dh20156 2010-02-09

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Unfortunately, the __parent__ property does not work with nested functions when used with Firefox (SpiderMonkey). When __parent__ is used with Firefox, it always returns either the Window object or null.

dh20156 2010-02-09

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The JavaScript language does not provide you with a method of accessing a function’s Variable object. The only way to access this object is by taking advantage of the __parent__ magic property. For example, the following script (which works in Firefox) returns the Global scope object:

1: <script type="text/javascript">

2:

3: function doSomething() {}

4:

5: alert(doSomething.__parent__); // returns Window

6:

7: </script>

8:

The Global scope object in the case of a browser is the Window object. All global variables become properties of the Window object.

Unfortunately, the __parent__ property does not work with nested functions when used with Firefox (SpiderMonkey). When __parent__ is used with Firefox, it always returns either the Window object or null. If you want to use __parent__ with nested functions, then you need to use Rhino.

Rhino is the Java version of the Mozilla JavaScript engine. You can download Rhino from http://developer.mozilla.org/en/docs/Rhino. To get Rhino to work in Windows, I had to follow the instructions from the following blog entry by Luke Maciak: http://www.terminally-incoherent.com/blog/2008/01/08/rhino-scripting-java-with-javascript.

After Rhino is setup, you can execute JavaScript statements from the command line. I executed the following commands:

1: function f()

2:

3: {

4:

5: var bob='hello';

6:

7: var inner = function(){};

8:

9: var parent = inner.__parent__;

10:

11: var contents = '';

12:

13: for (k in parent) contents += k + ' ';

14:

15: print(contents);

16:

17: }

18:

19: f();

The script above contains a function named f(). This function contains an inner function named inner. The __parent__ property of the inner function returns f’s Variable object. Therefore, when the script is executed, the following list of items is printed:

arguments bob contents parent inner

These are the properties that you would expect for the f function’s Variable object. The first items, represents the parameters passed to the f() function. The remaining items correspond to each of the f() function’s local variables.

freespacezjx 2010-02-09

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额,学习...................................................

wtcsy 2010-02-09

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引用 10 楼 freespacezjx 的回复:

js 中的函数都可以看作一个对象,函数都是继承Object的,应该是由于这一点,上面的cc.parent===xx.parent;

你说的不对哦

函数是可以看成一个对象但是他是先继承的Function的prototype 然后在是继承到Object的prototye

Object.prototype.a="a";

Function.prototype.a="aa";

function xx(){}

alert(xx.a)

delete Function.prototype.a

alert(xx.a)

另外是__parent__属性不是 parent属性
这个属性很特殊(函数的[[scope]] 属性,不访问,在firefox下提供__parent__属性来访问) 它引用的是函数定义时的作用域链
这个与继承什么的无关只与函数定义时候的作用域有关

ps:这个眼睛是卡卡西或者说是带土的眼睛不是鼬或者zz的

freespacezjx 2010-02-09