Capturing Boolean Return Value from JS AJAX function call

Question

Really simple javascript function that does an AJAX call. When the function returns, it returns with a boolean value (not a string). Right now, for testing purposes, I have it set to always return 'true'. Problem is that I don't seem to be able to capture this value so that I can evaluate it. Here is the code:

function verifySession() {

    var xmlhttp = new XMLHttpRequest();

    var returnValue = xmlhttp.onreadystatechange=function() {
        if (xmlhttp.readyState==4 && xmlhttp.status==200) {

            // this is wrong, but I don't know how to alter it for boolean values
            session_verified = xmlhttp.responseText;

            // this outputs as empty, even though the return value is true
            console.log(session_verified); 

            if (!session_verified) {
                console.log("false value returned");
                return false;
            } else {
                console.log("true value returned");
                return true;
            }
        }
    }

    xmlhttp.open("GET", "/scripts/session_verifier.php", false);
    xmlhttp.send();
    return returnValue;
}

session_verifier.php basically looks like this (again, grossly simplified for testing purposes):

<?php
return true;
?>

I've used this many times for functions that return strings, but this time I need it to return a boolean value. How can I capture its return value? Thanks!

Answer 1

In your php script. Try returning the string value true ("true"), or the number 1

then in your JS

session_verified = Boolean(xmlhttp.responseText);

Answer 2

Testing your code I've noticed that the result is empty, as you can see here:

readyState: 4
response: ""
responseText: ""
responseType: ""
responseXML: null

But if you change a bit your PHP, you can see the result:

header('Content-Type: application/json');
echo json_encode(array(
    'success' => true,
));

I hope it helps you.

Cheers,

Answer 3

Since the XMLHttpRequest response might be a text or XML, you can handle the Boolean return value this way.

// PHP
function your_function(){
  if($something == TRUE){
    return 1;
  }else{
    return 0;
  }
}

// JavaScript
xhr = new XMLHttpRequest();
xhr.open("GET", url, true);
xhr.onreadystatechange = function () { 
  if (xhr.readyState == 4 && xhr.status == 200) {
      if(parseInt(xhr.responseText)){
        // true
      }else{
        // false
      }
  }
};
xhr.send();