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- Title: 在js循环中，得到递增变量的永久引用
- 0/9
- stauren
IP hidden - 2008-05-07 11:13
5 days ago
如果我们需要在一个页面上，使用javascript为一系列的Dom事件添加处理函数，我们可能会用这种模式：
这样出现了一个问题，每一个callback里面保存了一个对i变量的引用，而且是同一个i！！后果是：这20个事件触发的alert的内容都是20
所以我们需要对每一个alert创建单独的变量的引用空间，一个麻烦之处在于，循环的时候我们倾向于使用递增的同一变量名的变量值，在本次循环执行过程中，该变量的值是我们想要的，但到下一个循环后，它的值就改变了，所以，如何得到一个该轮循环的变量值的一个本地副本呢？
我的答案是，闭包，伟大的closure
var i = 0;
while (i<20) {
var callback = function(alert(i));
do_callback_when_something_happen(callback);
i++;
这样，我们把20个事件加到了20个Dom事件上。这样出现了一个问题，每一个callback里面保存了一个对i变量的引用，而且是同一个i！！后果是：这20个事件触发的alert的内容都是20
所以我们需要对每一个alert创建单独的变量的引用空间，一个麻烦之处在于，循环的时候我们倾向于使用递增的同一变量名的变量值，在本次循环执行过程中，该变量的值是我们想要的，但到下一个循环后，它的值就改变了，所以，如何得到一个该轮循环的变量值的一个本地副本呢？
我的答案是，闭包，伟大的closure
var i = 0;
while (i<20) {
(function()
var _i = i,
callback = function(alert(_i));
do_callback_when_something_happen(callback);
})();
i++;
}
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1983-06-21:(40 days away)
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stauren@西湖湖畔
JavaScript is the world's most misunderstood programming language. The language has so much expressive power that it is possible to be somewhat productive with it without knowing what you're doing. But that is not an effective way to work. Programming is serious business that should never be undertaken in ignorance.
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一般的SB都是酷酷的
Belle
JavaScript is the world's most misunderstood programming language. The language has so much expressive power that it is possible to be somewhat productive with it without knowing what you're doing. But that is not an effective way to work. Programming is serious business that should never be undertaken in ignorance.
Listen Yahoo!
Let's start from here!
一般的SB都是酷酷的
Belle
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All we got here, are memories. With heart & soul. 2006-2008 STauren! © Ver 0.7.1