getId = function(filePath, params) { if (window.XMLHttpRequest) { var xmlhr = new XMLHttpRequest(); } else { var xmlhr = new ActiveXObject('MSXML2.XMLHTTP.3.0'); } xmlhr.open('POST', filePath, true); xmlhr.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded'); xmlhr.onreadystatechange = function() { if (xmlhr.readyState == 1) { } else if (xmlhr.readyState == 4 && xmlhr.status == 200) { if (xmlhr.responseText) { var Id = xmlhr.responseText; alert(Id); // <-- this works return Id; // <-- this doesn't return if I do a call: var myId = getId(xx,xx); } } else if (xmlhr.readyState == 4) { alert('Invalid response received - Status: ' + xmlhr.status); } } xmlhr.send(params);}