如何从for循环中的匿名函数获取当前循环迭代？ [英] How to get current loop iteration from anonymous function within the for loop?

问题描述

可能重复：

循环内部的Javascript闭包 - 简单的实际示例

<我有一个带有匿名函数的for循环，在函数中我想访问当前的循环迭代。但由于某些原因而不是循环迭代，我得到4.唯一的另一个地方4是一个值是myArray.length。如果我将i作为参数传递，我会得到[object Object]。我究竟做错了什么？我的代码：

I have a for loop with an anonymous function inside, and in the function I want to access the current loop iteration. But for some reason instead of the loop iteration, I'm getting 4. The only other place 4 is a value is myArray.length. If I pass i as an argument, I get [object Object] out. What am I doing wrong? My code:

var width = function(){
   for(var i = 0, len = myArray.length; i < len; ++i){
      alert(i) //this outputs the current iteration
      myArray[i].load(function(){
         alert(i) //this outputs 4 (or [object Object])
      });
   };
};

谢谢。

推荐答案

传递给 .load 的匿名函数正在循环完成后执行。

Your anonymous function passed to .load is being executed way after your loop has finished.

您必须创建一个本地范围，并复制 i 变量：

You have to create a local scope, and copy the i variable:

var width = function(){
    for(var i = 0, len = myArray.length; i < len; ++i){
        (function(i){
            myArray[i].load(function(){
                alert(i) //this outputs 4 (or [object Object])
            });
        })(i);
    };
};

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