javascript - XMLHttpRequest timeout case - onreadystatechange executes before ontimeout? -

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i using xmlhttprequest make asynchronous requests. have

xhr.onreadystatechange = function () {     if (xhr.readystate === 4) {//handle if state has completed         if (xhr.status === 200) {             successhandler.call(context, xhr.responsetext);         } else {             console.warn('onreadystatechange:' + new date().gettime());             failurehandler.call(context, xhr.status, xhr.statustext);         }     } }; xhr.ontimeout = function () {     console.warn('ontimeout: ' + new date().gettime());     failurehandler.call(context, 0, 'timeout'); };

i forcing timeout using network throttling. observe both onreadystatechange , ontimeout callbacks called in case of timeouts, onreadystatechange preceding ontimeout. under impression 1 of 2 executed. using chrome. know if expected?

the modern solution use appropriate xmlhttprequest events: onload , onerror if want handle these cases separately, onloadend if wish detect http request completion regardless of success, , ontimeout timeouts. when timeout occurs, ontimeout called, not onloadend. onreadystatechange looks it's best left die quietly. full set of events can found here:

http://www.w3.org/tr/xmlhttprequest/#events

since onreadystatechange→ontimeout sequence doesn't appear afflict ie 8, purposes i'm happy following: use onreadystatechange in ie 8, , onloadend in firefox/modern msie (using following test see if event defined: if ("onloadend" in httpobj) ...).

this internal system, suffices me; op, more testing may required.


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