在javascript匿名方法中访问复制的整数变量 [英] Access a copied integer variable in javascript anonymous method

问题描述

我是一个C＃开发人员，习惯了闭包在C＃中工作的方式。
目前我必须使用匿名javascript函数，并遇到以下代码片段的问题：

I am a C# developer and used to the way closures work in C#. Currently I have to work with anonymous javascript functions and experience a problem with the following snippet:

    function ClosureTest() {
    var funcArray = new Array();

    var i = 0;
    while (i < 2) {
        var contextCopy = i;

        funcArray[i] = function() { alert(contextCopy); return false; };

        i++;
    }

    funcArray[0]();
    funcArray[1]();
}

我希望第一个 funcArray c $ c>调用 0 ，第二个说 1 。但是，他们都说 1 。

I expect the first funcArray() call to say 0 and the second to say 1. However, they both say 1. How is that possible?

通过写 var contextCopy = i 我确保我创建了一个 i -variable。然后，在每个while-iteration中，我创建一个全新的函数指针。每个函数引用其自己的 i 副本，即 contextCopy 。但是，由于某些原因创建的函数指的是相同的 contextCopy -variable。

By writing var contextCopy = i I make sure that I create a copy of the i-variable. Then, in each while-iteration I create a completely new function pointer. Each function refers to its own copy of i, which is contextCopy. However, both created functions for some reason refer to the same contextCopy-variable.

？

推荐答案

JavaScript具有词法闭包，而不是闭包。即使您将i分配给contextCopy，contextCopy本身也是ClosureTest的一个词汇成员（它与C＃不同，其中{}为您提供了一个新的范围块）。尝试这样：

JavaScript has lexical closures, not block closures. Even though you are assigning i to contextCopy, contextCopy is, itself, a lexical member of ClosureTest (which is different from C#, where the {} give you a new scoped block). Try this:

while (i < 2) {
    funcArray[i] = (function(value) { 
        return function(){ alert(value); return false; }
    })(i);
    i++;
}

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