CODEWITHSUNDEEP
javascriptjqueryhtmlajaxfunction
Atul Nar
Atul Nar

Reputation: 695

Error in accessing element in anonymous function in ajax program

I am trying to fetch data from file using ajax on mouseover. Everything works fine, except when I try to access a <p> element inside an anonymous function, I get nothing. Possible reason is that the element lost scope inside anonymous function. Please advise if you see a possible solution.

<html>
    <head>
        <title>MouseOver Effect And Ajax </title>
        <link rel="stylesheet" type="text/css" href="style.css"/>
        <script type="text/javascript" src="http://localhost/study/libraries/jquery-1.8.3.js"></script>
        <script type="text/javascript">
            $(document).ready(function(){
                var xhr=false;
                initAll();

                $('div.pcard').mouseover(function(){
                    if(xhr)
                    { 
                        var pname=$(this).children('p.pname').text();
                        var pname=pname+"_details.txt";
                        xhr.open("GET",pname);;
                        xhr.onreadystatechange=function(){
                            if(xhr.readyState==4)
                            { 
                                if(xhr.status==200)
                                { 
                                $(this).children('p.pdesc').text(""+msg);

                                alert($(this).children('p.pname').text());

                                $(this).children('p.pdesc').css({'visibility':'visible'});
                                }
                            }
                        }.bind(this);
                        xhr.send(null);
                    }
                });

                $('div.pcard').mouseout(function(){
                    $(this).children('p.pdesc').css({'visibility':'hidden'});   
                });


                function initAll()
                { 
                    if(window.XMLHttpRequest)
                    { 
                        xhr=new XMLHttpRequest();
                    }
                    else if(window.ActiveXObject)
                    { 
                        try{
                            xhr=new ActiveXObject("Microsoft.XMLHTTP");
                        }catch(e){}
                    }
                }


            });
        </script>
    </head>
    <body>
        <h2>Interactive MouseOver</h2>
        <div id="products">
            <div class="pcard">
                <p class="pname">Sandwhiches</p>
                <p class="pdesc"></p>           
            </div>
            <div class="pcard">
                <p class="pname">Pizzas</p>
                <p class="pdesc"></p>           
            </div>
            <div class="pcard">
                <p class="pname">Soups</p>
                <p class="pdesc"></p>           
            </div>
            <p style="clear:both"></p>
        </div>
    </body>
</html>

Upvotes: 0

Views: 916

Answers (2)

Ian
Ian

Reputation: 50905

Us commenters have concluded that sharing one XMLHttpRequest is not a good idea and you would probably want to fire off a new one for every mouseover event occurring. Things can get messy when you call open on an already opened/uncompleted request, while send should be okay. What is normally done is something like this:

$(document).ready(function () {
    $('div.pcard').mouseover(function () {
        var self = $(this);

        var pname = self.children('p.pname').text();
        var pname = pname + "_details.txt";

        var xhr = ajaxFunction();
        xhr.open("GET", pname);
        xhr.onreadystatechange = function () {
            if (xhr.readyState == 4) {
                if (xhr.status == 200) {
                    var msg = "" + xhr.responseText;

                    self.children('p.pdesc').text(""+msg);

                    //alert(self.children('p.pname').text());

                    self.children('p.pdesc').css({'visibility':'visible'});
                }
            }
        };
        xhr.send(null);
    });

    $('div.pcard').mouseout(function(){
        $(this).children('p.pdesc').css({'visibility':'hidden'});   
    });
});

function ajaxFunction() {
    var ajaxRequest; // The variable that makes Ajax possible!
    try {
        // Firefox, Chrome, Opera 8.0+, Safari
        ajaxRequest = new XMLHttpRequest();
    } catch (e) {
        // Internet Explorer Browsers
        try {
            ajaxRequest = new ActiveXObject("Microsoft.XMLHTTP");
        } catch (e) {
            try {
                ajaxRequest = new ActiveXObject("Msxml2.XMLHTTP");
            } catch (e) {
                try {
                    ajaxRequest = new ActiveXObject("Msxml2.XMLHTTP.6.0");
                } catch (e) {
                    try {
                        ajaxRequest = new ActiveXObject("Msxml2.XMLHTTP.3.0");
                    } catch (e) {
                        throw new Error("This browser does not support XMLHttpRequest.");
                    }
                }
            }
        }
    }
    return ajaxRequest;
}

In the ajaxFunction, I'm not sure if you really have to go past the first 2 ActiveXObject attempts, that's just something I've seen...and there's several more you can "try" for. There were a few other things that were weird in your original code (that was edited by others without looking) - you commented out the line that set the msg variable, and then you tried to use it on the next line. The .bind probably works, but I like the way I provided...that's up to you...try both and see if either one works separately.

But as the other answer already points out, if you're already using jQuery, why not use $.ajax?

Upvotes: 1

Ibu
Ibu

Reputation: 43820

You have jquery, why are you rewriting your own ajax call?

Save the this into a local variable : var that = this then you can reuse it.

$(document).ready(function(){
    $('div.pcard').mouseover(function(){

    var pname=$(this).children('p.pname').text();
    pname=pname+"_details.txt";
    var that = this; /// keeping the scope
    $.ajax({
       url:pname,
       success: function () {
           $(that).children('p.pdesc').text(""+msg);
           alert($(that).children('p.pname').text());
           $(that).children('p.pdesc').css({'visibility':'visible'});

       }
    });
});

Upvotes: 0

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