return value from ajax call to javascript

Question

I am calling ajax to fetch a value from asp page and return to the calling javascript, and the code is like below

function getNameFromSession()
{
    xmlhttp=GetXmlHttpObject();
    if (xmlhttp==null)
    {
        alert ("Your browser does not support AJAX");
        return;
    }
    var url="getImageName.asp";
    url=url+"?fetch_name=1";
    xmlhttp.open("GET",url,true);
    xmlhttp.send(null); 
    xmlhttp.onreadystatechange=function(){

        if (xmlhttp.readyState==4)
        {
           alert(xmlhttp.responseText);
           return xmlhttp.responseText;

        }

    }
}

alert in function shows correct value, but javascript get undefined as value, can anybody tell me how can I return the value from this ajax to javascript calling function

Answer 1

The line in your code

return xmlhttp.responseText;

Doesn't have anywhere to return the value to. You'll either need to pass a callback function with the request to process it further or do you thing with the.

if(xmlHttp.readyState == 4)

conditional.

Answer 2

That is because your main function, getNameFromSession isn't returning anything.

What you can do is assign the response from your onreadystatechange handler to a variable, and then retrieving the variable after getNameFromSession is called.

Answer 3

AJAX is asynchronous, meaning the request is sent and then the code continues on. Your return statement happens after the function has already completed. You should move whatever you need to do with that return value into the function itself.

Answer 4

just synchronize the ajax by making third parameter as false in xmlhttp.open("GET",url,true). By this it will wait for server to give response before returning the control to calling java script.

function getNameFromSession()
{
    xmlhttp=GetXmlHttpObject();
    if (xmlhttp==null)
    {
        alert ("Your browser does not support AJAX");
        return;
    }
    var url="getImageName.asp";
    url=url+"?fetch_name=1";
    xmlhttp.open("GET",url,false);
    xmlhttp.send(null); 
    xmlhttp.onreadystatechange=function(){

        if (xmlhttp.readyState==4)
        {
           alert(xmlhttp.responseText);
           return xmlhttp.responseText;

        }

    }
}