Trouble with jQuery Ajax timing

StackOverflow https://stackoverflow.com/questions/1279625

  •  16-09-2019
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Question

I have a very simple javascript class that does an ajax call to a web service of mine via jquery. It returns the data successfully, but I am unable to retrieve it via a variable I set the data to. I don't think it is a matter of the ajax call being asynchronous or not because I have set up event handlers for all the ajax events, but some of them do not fire. I have no idea what is wrong. Here is the complete code:

Javascript:

function testClass(){
    this.returnData = "";
    this.FireAjax = function(){
        $.getJSON("http://localhost/mywebapp/webservices/service.asmx/Initialize?userID=12&jsoncallback=?",
            function(data){
                this.returnData = data.d;
                alert(data.d);
            }
        );  
    }

}

HTML page:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Untitled Document</title>
<script type="text/javascript" src="http://localhost/mywebapp/js/jquery-1.3.2.min.js"></script>
<script type="text/javascript" src="testClass.js"></script>

<script type="text/javascript">
    $(document).ready(function(){

        var obj = new testClass();

        $("#debug").ajaxError(function(event, request, settings){
            $(this).append("<b>Ajax Error!</b><br />"); //this does not fire
        });

        $("#debug").ajaxSend(function(evt, request, settings){
            $(this).append("<b>Ajax Send!</b><br />"); //this does not fire!?
        });

        $("#debug").ajaxStop(function(){
            $(this).append("<b>Ajax Stopped</b><br />"); //this fires
        });

        $("#debug").ajaxComplete(function(event,request, settings){
            $(this).append("<b>Ajax Completed!</b><br />"); //this fires
            $(this).append("<h2>" + obj.returnData + "</h2>"); //this returns an empty string!!!!!!
        });

        $("#debug").ajaxSuccess(function(evt, request, settings){
            $(this).append("<b>Ajax Successful!</b><br />"); //this fires
        });

        $("#debug").ajaxStart(function(){
            $(this).append("<b>Ajax Started!</b><br />"); //this fires
        });

        obj.FireAjax();
    });
</script>
</head>

<body>
<div id="debug">

</div>
</body>
</html>

Additional Info: If I remove the complete event in my html page and place the call to obj.returnData in my stop event (thinking that perhaps my html complete event overwrites my testClass complete function), i get the same results.

Was it helpful?

Solution

Your problem is here:

this.returnData = data.d;

this inside the anonymous function refers to the jQuery Options object, not the instance of your object.

Try this:

function testClass(){
    this.returnData = "";
    var that = this;
    this.FireAjax = function(){
        $.getJSON("http://localhost/mywebapp/webservices/service.asmx/Initialize?userID=12&jsoncallback=?",
                function(data){
                        that.returnData = data.d;
                        alert(data.d);
                }
        );      
    }

}
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