xmlhttprequest - TypeError: xhrReq.abort is not a function -

var xhrreq; function tpvajaxpost(json) {   if(xhrreq !== undefined) {       xhrreq.abort();       xhrreq = undefined;   }   xhrreq = $.post("inc/ajax/tpv.php", json, function (data) {       if(typeof (data['message']) !== 'undefined') {           tpvhandleerrors(data['message']);       } else {           tpvhandleresults(json['action'], data);       }   }, "json").always(function() { xhrreq = undefined; }); } 

why getting : typeerror: xhrreq.abort not function ????