Why can I not return responseText from an Ajax function?

Question

Here is part of my Ajax function. For some reason that I cannot figure out, I am able to alert() responseText but not able to return responseText. Can anybody help? I need that value to be used in another function.

http.onreadystatechange = function(){
    if( http.readyState == 4 && http.status == 200 ){
        return http.responseText;
    }
}

Answer 1

You will not be able to handle the return value that you are returning from your asynchronous callback. You should handle the responseText within the callback directly, or call a helper function to handle the response:

http.onreadystatechange = function () {
    if (http.readyState == 4 && http.status == 200) {
        handleResponse(http.responseText);
    }
}

function handleResponse (response) {
    alert(response);
}

Answer 2

See my answer to these related questions:

http://stackoverflow.com/questions/3715820/how-can-i-write-an-async-method-in-javascript-when-posting-or-looping/3716138#3716138

http://stackoverflow.com/questions/3720696/ajax-call-inside-a-function/3720827#3720827