全局变量不会在AJAX成功内从函数更新 [英] global variable won't update from function within AJAX success

问题描述

好的，所以我似乎无法在通过ajax后更改systemPath的全局变量，它可以在ajax内运行，但是我需要ajax之外的更新后的变量.基本上，我试图从xml创建路径数组，并使用它们查找其他可以从中生成表的xml文件.

OK, so I cannot seem to be able to change the global variable of systemPath after it goes through the ajax.It will work inside of ajax, but I need that updated variable outside of ajax. basically I'm trying to create an array of paths from xml and use them to locate other xml files that I can generate a table from.

有人知道这是怎么回事吗? ajax是否在变量设置之前运行，这就是为什么ajax之后的数组长度为0的原因?

Does anyone know what's going on here? Does ajax run before the variable is set and that is why I get an array length of 0 after the ajax?

    var systemPath = new Array();
var techDigestArr = new Array();
var addToArray = function(thisarray, toPush){
    thisarray.push(toPush);
}

$.ajax({
    url: fullPath+"technical/systems/systems.xml",
    dataType: ($.browser.msie) ? "text" : "xml",
    success: function(data){
                            var xml;    
                            if (typeof data == "string") {
                               xml = new ActiveXObject("Microsoft.XMLDOM");
                               xml.async = false;
                               xml.loadXML(data);
                            } else {
                               xml = data;
                            }
                            $(xml).find("system").each(function(){
                                var urlString = fullPath + "technical/system_" + $(this).attr("id") + "/" + $(this).attr("id") + "tech-digest.xml <br />";
                                //alert(urlString);
                            $("#td-articles").append(systemPath.length + urlString);
                                addToArray(systemPath,urlString);
                                //systemPath.push(urlString);
                            });
                        $("#msg-output").append("total - " +systemPath.length);//Returns 48

                    },//END SUCCSESS
    error: function(){
        alert("Sorry - ");
        history.go(-1);
    }
});//END AJAX CALL
    $(document).ready(function(){
        //$("#msg-output").append("total - " + systemPath.length); Returns 0
    });

推荐答案

ajax是异步运行的.事情在您的代码中按此顺序执行.

The ajax is ran asynchronously. Things execute in this order in your code.

1. $.ajax()
之前的内容
2. $.ajax()启动ajax调用(在等待响应的同时，它继续运行其余代码)
$.ajax() 之后的内容
3. success回调

1. stuff before $.ajax()
2. $.ajax() initiates an ajax call (while waiting for the response it continues to run the rest of the code)
3. stuff after $.ajax()
4. success callback

请注意，取决于通话3和4的速度，通话的顺序可能相反(此处不是这种情况)

Note that depending on how fast the call is 3 and 4 might occur in reverse order (not the case here)

因此，当执行$(document).ready()时，ajax调用可能尚未返回，因此成功回调中的代码没有机会执行.如果您很幸运并且连接速度很快，那么响应可能会在文档准备好之前就出现了，但这不太可能.

So when $(document).ready() is executed the ajax call might not have returned yet, so the code in the success callback didn't have a chance to execute. If you are lucky and have a fast connection than maybe the response will come before document ready, but it's unlikely.

只要您可以看到全局变量已更新，就可以设置超时时间:

Just so you can see that the global variable gets updated you can set a timeout:

$(document).ready(function(){
  setTimeout(function(){
    $("#msg-output").append("total - " + systemPath.length);
    //if the delay set below is more than the time between the ajax request and the server response than this will print the correct value 
  },2000);
});

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