Json encode is not initialized

I am facing an issue with a simple ajax request that retrieves a json encoded array. The error message I keep receiving is that the response is not defined. I suspect I have misplaced the return statement in my function. Here is how the function looks:

//Browser Support Code
function ajaxFunction(url,data){
    var ajaxRequest;  // The variable that makes Ajax possible!

    try{
        // Opera 8.0+, Firefox, Safari
        ajaxRequest = new XMLHttpRequest();
    } catch (e){
        // Internet Explorer Browsers
        try{
            ajaxRequest = new ActiveXObject("Msxml2.XMLHTTP");
        } catch (e) {
            try{
                ajaxRequest = new ActiveXObject("Microsoft.XMLHTTP");
            } catch (e){
                // Something went wrong
                alert("Your browser broke!");
                return false;
            }
        }
    }

    ajaxRequest.onreadystatechange = function(){
        if(ajaxRequest.readyState == 4){
            var response = ajaxRequest.responseText

        }
    }   
    queryString = "?dta="+data;
    ajaxRequest.open("GET", url + queryString, true);
    ajaxRequest.send(null);
return(response);   
}        

Here is how I am calling the function:

    var result = ajaxFunction('call.php','1');
    alert(result);

The response is being successfully retrieved as the console displays:

{"stage1":"550","stage2":"1500","stage3":"2000","total":"1"}

However, I am encountering the error: response is not defined

Any insights on how to resolve this issue?

Answer №1

Two reasons explain why the response is undefined:

  • Syntax: it is defined in an inner function, making it invisible in the outer scope. Your return (response) actually translates to return (window.response)
  • Logical: the response is set in an asynchronous callback, so when a synchronous function returns, it may not be set, even if defined within the ajaxFunction.

To solve this, create a callback that will eventually return the result. Learn how jQuery.ajax returns its result by utilizing success(data, textStatus, jqXHR) as an argument passed to the function.

You can also enforce synchronous requests by setting the third parameter of the open call to "false." Refer to MSDN or MDN for more information.

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