循环一个JavaScript里面异步进程 [英] Asynchronous Process inside a javascript for loop

问题描述

我运行以下形式的事件循环：

I am running an event loop of the following form:

var i;
var j = 10;
for (i = 0; i < j; i++) {

    asycronouseProcess(callBackFunction() {
        alert(i);
    });
}

我想这显示是一系列经过10警报，显示数字0的问题是，由当时的回调函数被触发循环经历了几次迭代已经走了，它显示的更高的价值一世。关于如何解决此问题的任何建议？

What I would like this to display is a series of alerts showing numbers 0 through 10. The problem is that by the time the call back function is triggered the loop has already gone through a few iterations and it displays a higher value of i. Any recommendation on how to fix this?

推荐答案

您必须通过它传递给函数的地方，冻结 I 的值，所以它的值唯一存在用于在功能闭合循环的每次迭代。否则，所有的非同步回调只会看到 i的值在循环是，当他们执行它们的回调（有时后，当循环完成它的价值到底），而不是每个自身的价值。

You have to freeze the value of i by passing it into a function somewhere so it's value exists uniquely for each iteration of the loop in a function closure. Otherwise, all asynch callbacks will just see the value of i at the end of the loop which is the value it has when they execute their callbacks (sometime later when the loop has finished), not each their own value.

假如你不能改变异步回调函数，那么你可以用这样的自我执行的功能，这对于每次循环创造了一个独特的功能封做到这一点：

Assuming you can't change the asynchronous function callback, then you could do it with a self executing function like this which creates a unique function closure for each iteration of the loop:

var i;
var j = 10;
for (i = 0; i < j; i++) {
    (function(cntr) {
        // here the value of i was passed into as the argument cntr
        // and will be captured in this function closure so each
        // iteration of the loop can have it's own value
        asycronouseProcess(function() {
            alert(cntr);
        });
    })(i);
}

如果您可以修改 asycronouseProcess（）函数，那么你可以只通过在那里的价值，并有 asycronouseProcess（）功能CNTR回这样的回调：

If you can modify the asycronouseProcess() function, then you could just pass the value in there and have the asycronouseProcess() function the cntr back to the callback like this:

var i;
var j = 10;
for (i = 0; i < j; i++) {
    asycronouseProcess(i, function(cntr) {
        alert(cntr);
    });
}

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