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Simple Javascript XHR Object With Fix For Missing Onreadystatechange Event In Firefox (for Synchronous Calls)

This code fixes the issue in Firefox where the onreadystatechange event is not called for synchronous XHR requests. It is based on the XHConn script from http://xkr.us/code/javascript/XHConn/, patched with the fix documented at http://lukav.com/wordpress/2007/04/12/firefox-firebug-and-synchronos-calls-problem/


/** XHConn - Simple XMLHTTP Interface - bfults@gmail.com - 2005-04-08        **
 ** Code licensed under Creative Commons Attribution-ShareAlike License      **
 ** http://creativecommons.org/licenses/by-sa/2.0/                           **/
/**
 * Modified slightly from original to support synchoronous transactions
 * CDB 2007-05-16, 2007-06-05
 */

function XHConn()
{
	var xmlhttp, bComplete = false;
	try { xmlhttp = new ActiveXObject("Msxml2.XMLHTTP"); }
	catch (e) { try { xmlhttp = new ActiveXObject("Microsoft.XMLHTTP"); }
	catch (e) { try { xmlhttp = new XMLHttpRequest(); }
	catch (e) { xmlhttp = false; }}}
	if (!xmlhttp) return null;
	this.connect = function(sURL, sMethod, sVars, fnDone, bAsynch)
	{
		if (!xmlhttp) return false;
		bComplete = false;
		sMethod = sMethod.toUpperCase();

		if (bAsynch == null) bAsynch = true; //treat asynch as an optional argument

		try {
			if (sMethod == "GET")
			{
				xmlhttp.open(sMethod, sURL+"?"+sVars, (bAsynch == true));
				sVars = "";
			}
			else
			{
				xmlhttp.open(sMethod, sURL, (bAsynch == true));
				xmlhttp.setRequestHeader("Method", "POST "+sURL+" HTTP/1.1");
				xmlhttp.setRequestHeader("Content-Type",
					"application/x-www-form-urlencoded");
			}

			xmlhttp.onreadystatechange = function(){
				if (xmlhttp.readyState == 4 && !bComplete)
				{
					bComplete = true;
					fnDone(xmlhttp);
				}
			};
			xmlhttp.send(sVars);

			/**
			 * Firefox <= 2.0.0 doesn't fire onreadystatechange for synchronous requests.
			 * See http://lukav.com/wordpress/2007/04/12/firefox-firebug-and-synchronos-calls-problem/
			 */
			var isGecko = (document.addEventListener) ? true : false;
			try {
				if (!bAsynch && isGecko && xmlhttp.onreadystatechange == null) {
					bComplete = true;
					fnDone(xmlhttp);
					return true;
				}
			}
			catch (e) { return false; }
			/**
			 * End synchronous request patch
			 */
		}
		catch(z) { return false; }
		return true;
	};
	return this;
}
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