如何在循环中访问jquery getJson调用（$ .getJson）中的索引变量？ [英] How to access index variable in a jquery getJson call ($.getJson) during a loop?

问题描述

我有以下代码，已针对此问题进行了简化。基本上我有一个循环，在每次迭代，调用jquery getJSON函数，调用到一个API端点，以抓取一些天气数据。问题是，我需要从循环访问索引，当getJSON请求被触发，我有一些麻烦。我需要知道请求的索引，所以我可以与数据库中的一些数据匹配。

I have the following code, which has been simplified for this question. Basically i have a loop, that, on each iteration, calls the jquery getJSON function, calling out to a API end point to grab some weather data. The problem is that i need to access the index from the loop, when the getJSON request was fired, and am having some troubles with it. I need to know what index the request was for, so i can match it with some data from a database.

代码：

function buildCities()
{    
    for (var i = 0; i < 7; i++) 
    {
        var jqxhr = $.getJSON("http://api.openweathermap.org/data/2.5/weather?q=usa,phoenix&units=metric", function(response) 
       {
           alert(i); //this will always be 7 - this is the issue.  i desire it to be 0,1,2,3, etc.... 
       });
    }
}

这里是一个JSFiddle显示的问题，您可以根据需要处理;）
- http://jsfiddle.net/5tr34k/0xshvrzp/

Here is a JSFiddle that shows the issue, and that you can work on if need be ;) - http://jsfiddle.net/5tr34k/0xshvrzp/

请求：
如何在请求的回调函数中插入或访问此索引（i）？感谢您的任何帮助。

The request: How can i inject or otherwise access this index (i) inside of the callback function for the request ? Thanks for any help.

推荐答案

添加一个范围函数（IIFE），为您的变量创建一个新的范围：

Add a scoping function (an IIFE) that creates a new scope for your variable:

function buildCities()
{    
    for (var i = 0; i < 7; i++) 
    {
        (function(index){
            var jqxhr = $.getJSON("http://api.openweathermap.org/data/2.5/weather?q=usa,phoenix&units=metric", function(response) 
           {
                alert(index); 
           });
        })(i);
    }
}

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