jQuery AJAX 调用 for 循环 [英] jQuery AJAX calls in for loop

问题描述

我是使用 AJAX 的新手，我正在编写一个用户脚本，它将处理页面上的一堆链接并为每个链接进行 AJAX 调用.

I'm new to using AJAX, and I'm writing a userscript that will process a bunch of links on a page and make AJAX calls for each one.

for (var i = 0; i < linkList.length; i++)
{
    $.ajax({
        url: linkList[i].getAttribute("href"),
        cache: false
    }).done(function( html )
    {
        var hasAppended = false;
        if (html.indexOf('someStringOnGottenPage') != -1 && !hasAppended)
        {
            hasAppended = true;
            var id = linkList[i].getAttribute("href").substring(linkList[i].getAttribute("href").indexOf('='));
            $( "#links a[href*='" + id + "']" ).append(' THIS PAGE CONTAINS SPECIFIED DATA');
        }
    });
}

简单地说，我有一个包含链接列表的页面.我希望遍历链接并让 AJAX 处理每个链接页面的内容，并报告该页面是否包含指定的内容.

To try to put it simply, I have a page with a list of links. I wish to iterate through the links and get AJAX to process the contents of each of the links pages, and report back if that page contains something specified.

我遇到的问题是用于遍历 linkList 的 [i] 的值始终为 6，而且永远不应该如此.我假设我需要传递一些数据，以便当 .done 最终触发时，它知道 AJAX 首次触发时的 [i] 值，而不是 .done 稍后触发时的 [i] 值.

The issue I'm having is the value of [i] used to iterate through the linkList is always 6, and it should never be. I'm assuming I need to pass some data so that when .done finally triggers, it knows its [i] value from when AJAX first triggered and not the value of [i] when .done triggers later.

我如何确保 .done 在第一次调用 AJAX 时知道它的 [i] 值?

How do I go about ensuring .done knows it's [i] value when AJAX is first called?

推荐答案

最简单的方法是使用闭包.每当你在循环中有一些异步的东西时，都是一样的.

The easiest way is to use a closure. Whenever you have something asynchronous in a loop, it is the same thing.

for (var i .....) {
  asynchronousFunction(function() {
    use(i);
  }
}

在这个伪代码片段中，内部函数捕获了i 引用的存储位置.循环运行，i 递增到其最终值，然后开始调用异步回调，所有这些回调都查找完全相同的位置(不是值).

In this pseudocode snippet, the inner function captures the storage location referenced by i. The loop runs, the i increments to its final value, and then the async callbacks start getting called, all of them looking up the exact same location (not value).

一般的解决方案是这样的:

The general solution is this:

for (var i .....) {
  (function (i) {
    asynchronousFunction(function() {
      use(i);
    });
  })(i);
}

即将循环的全部内容包装在一个自执行函数中.

i.e. wrap the whole contents of your loop in an self-executing function.

这里，外部 i 的 value 被传递到包装自执行匿名函数中；这个唯一值的位置被异步回调捕获.这样，每个 async 都有自己的值，在调用自执行函数时确定.

Here, the value of outer i gets passed into the wrapping self-executing anonymous function; this unique value's location gets captured by the async callback. In this way, each async gets its own value, determined at the moment the self-executing function is invoked.

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