javascript - XHR State Error when readyState is as expected -

i writing javascript program requires significant usage of xhr methods. using asynchronous style. core of have.

        global = {};         global.xhr = {};         global.xhr.requestqueue = [];         global.xhr.responsequeue = [];          xhr = new xmlhttprequest();         xhr.first = true;         xhr.onreadystatechange = function() {             //console.log(this.readystate);             if(this.readystate == 4) {                 if(this.first) {                     this.first = false;                     global.carouselitems = parseint(this.responsetext);                     global.onslidecountreceived();                 } else {                     global.xhr.responsequeue.push({status: xhr.status, responsetext: xhr.responsetext});                     if(global.xhr.requestqueue.length > 0) {                         xhr.open("get", global.xhr.requestqueue[0]);                         global.xhr.requestqueue.shift();                     }                 }             }             if(xhr.readystate == 1) {                 xhr.send();             }         }         //code adds bunch of items global.xhr.requestqueue         xhr.open("get","assets/carousel/items.php"); 

but when run this, chrome dev console prints bunch of errors following.

uncaught invalidstateerror: failed execute 'send' on 'xmlhttprequest': object's state must opened.

this despite call xhr.send() being in snippet above, wrapped in if statement. confusing me, because way see suggests make call xhr.send() when xhr.readystate 1, equivalent xmlhttprequest.opened , yet complaint not being case.

by way, requests complete successfully, , global.xhr.responsequeue populated expected response info. these intra-domain requests.