From a28eadff48d5e56bb529fc7a5c7e1a74e46398ed Mon Sep 17 00:00:00 2001
From: jaubourg <j@ubourg.net>
Date: Thu, 21 Apr 2011 18:43:40 +0200
Subject: [PATCH] Makes sure no unload handler is bound when not in IE. Also
 simplifies the whole "on unload abort" code. Also avoids the declaration of
 yet another variables in the jQuery main closure for the temporary XHR used
 to assess support properties.

---
 src/ajax/xhr.js | 56 +++++++++++++++++++++++--------------------------
 1 file changed, 26 insertions(+), 30 deletions(-)

diff --git a/src/ajax/xhr.js b/src/ajax/xhr.js
index 5dbc33d3..a87c3239 100644
--- a/src/ajax/xhr.js
+++ b/src/ajax/xhr.js
@@ -1,21 +1,14 @@
 (function( jQuery ) {
 
-var // #5280: next active xhr id and list of active xhrs' callbacks
-	xhrId = jQuery.now(),
-	xhrCallbacks,
-
-	// XHR used to determine supports properties
-	testXHR;
-
-// #5280: Internet Explorer will keep connections alive if we don't abort on unload
-function xhrOnUnloadAbort() {
-	jQuery( window ).unload(function() {
+var // #5280: Internet Explorer will keep connections alive if we don't abort on unload
+	xhrOnUnloadAbort = window.ActiveXObject ? function() {
 		// Abort all pending requests
 		for ( var key in xhrCallbacks ) {
 			xhrCallbacks[ key ]( 0, 1 );
 		}
-	});
-}
+	} : false,
+	xhrId = 0,
+	xhrCallbacks;
 
 // Functions to create xhrs
 function createStandardXHR() {
@@ -45,15 +38,13 @@ jQuery.ajaxSettings.xhr = window.ActiveXObject ?
 	// For all other browsers, use the standard XMLHttpRequest object
 	createStandardXHR;
 
-// Test if we can create an xhr object
-testXHR = jQuery.ajaxSettings.xhr();
-jQuery.support.ajax = !!testXHR;
-
-// Does this browser support crossDomain XHR requests
-jQuery.support.cors = testXHR && ( "withCredentials" in testXHR );
-
-// No need for the temporary xhr anymore
-testXHR = undefined;
+// Determine support properties
+(function( xhr ) {
+	jQuery.extend( jQuery.support, {
+		ajax: !!xhr,
+		cors: !!xhr && ( "withCredentials" in xhr )
+	});
+})( jQuery.ajaxSettings.xhr() );
 
 // Create transport if the browser can provide an xhr
 if ( jQuery.support.ajax ) {
@@ -136,7 +127,9 @@ if ( jQuery.support.ajax ) {
 								// Do not keep as active anymore
 								if ( handle ) {
 									xhr.onreadystatechange = jQuery.noop;
-									delete xhrCallbacks[ handle ];
+									if ( xhrOnUnloadAbort ) {
+										delete xhrCallbacks[ handle ];
+									}
 								}
 
 								// If it's an abort
@@ -197,15 +190,18 @@ if ( jQuery.support.ajax ) {
 					if ( !s.async || xhr.readyState === 4 ) {
 						callback();
 					} else {
-						// Create the active xhrs callbacks list if needed
-						// and attach the unload handler
-						if ( !xhrCallbacks ) {
-							xhrCallbacks = {};
-							xhrOnUnloadAbort();
+						handle = ++xhrId;
+						if ( xhrOnUnloadAbort ) {
+							// Create the active xhrs callbacks list if needed
+							// and attach the unload handler
+							if ( !xhrCallbacks ) {
+								xhrCallbacks = {};
+								jQuery( window ).unload( xhrOnUnloadAbort );
+							}
+							// Add to list of active xhrs callbacks
+							xhrCallbacks[ handle ] = callback;
 						}
-						// Add to list of active xhrs callbacks
-						handle = xhrId++;
-						xhr.onreadystatechange = xhrCallbacks[ handle ] = callback;
+						xhr.onreadystatechange = callback;
 					}
 				},