Ajax: simplify XHR detection.

Closes jquery#1967

Author: FarSeeing

src/ajax/xhr.js

@@ -1,13 +1,10 @@
 define([
 	"../core",
-	"../var/support",
-	"../ajax"
+	"../var/support"
 ], function( jQuery, support ) {
 
 jQuery.ajaxSettings.xhr = function() {
-	try {
-		return new XMLHttpRequest();
-	} catch ( e ) {}
+	return new XMLHttpRequest();
 };
 
 var xhrId = 0,
@@ -18,8 +15,7 @@ var xhrId = 0,
 		// Support: IE9
 		// #1450: sometimes IE returns 1223 when it should be 204
 		1223: 204
-	},
-	xhrSupported = jQuery.ajaxSettings.xhr();
+	};
 
 // Support: IE9
 // Open requests must be manually aborted on unload (#5280)
@@ -32,14 +28,14 @@ if ( window.attachEvent ) {
 	});
 }
 
-support.cors = !!xhrSupported && ( "withCredentials" in xhrSupported );
-support.ajax = xhrSupported = !!xhrSupported;
+// Support: IE9
+support.cors = "withCredentials" in jQuery.ajaxSettings.xhr();
 
 jQuery.ajaxTransport(function( options ) {
 	var callback;
 
 	// Cross domain only allowed if supported through XMLHttpRequest
-	if ( support.cors || xhrSupported && !options.crossDomain ) {
+	if ( support.cors || !options.crossDomain ) {
 		return {
 			send: function( headers, complete ) {
 				var i,

test/unit/support.js

@@ -55,7 +55,6 @@ testIframeWithCallback( "Check CSP (https://developer.mozilla.org/en-US/docs/Sec
 		// Catches Chrome on Android as well (i.e. the default
 		// Android browser on Android >= 4.4).
 		expected = {
-			"ajax": true,
 			"boxSizingReliable": true,
 			"checkClone": true,
 			"checkOn": true,
@@ -72,7 +71,6 @@ testIframeWithCallback( "Check CSP (https://developer.mozilla.org/en-US/docs/Sec
 		};
 	} else if ( /(msie 10\.0|trident\/7\.0)/i.test( userAgent ) ) {
 		expected = {
-			"ajax": true,
 			"boxSizingReliable": false,
 			"checkClone": true,
 			"checkOn": true,
@@ -89,7 +87,6 @@ testIframeWithCallback( "Check CSP (https://developer.mozilla.org/en-US/docs/Sec
 		};
 	} else if ( /msie 9\.0/i.test( userAgent ) ) {
 		expected = {
-			"ajax": true,
 			"boxSizingReliable": false,
 			"checkClone": true,
 			"checkOn": true,
@@ -106,7 +103,6 @@ testIframeWithCallback( "Check CSP (https://developer.mozilla.org/en-US/docs/Sec
 		};
 	} else if ( /8.0(\.\d+|) safari/i.test( userAgent ) ) {
 		expected = {
-			"ajax": true,
 			"boxSizingReliable": true,
 			"checkClone": true,
 			"checkOn": true,
@@ -123,7 +119,6 @@ testIframeWithCallback( "Check CSP (https://developer.mozilla.org/en-US/docs/Sec
 		};
 	} else if ( /(6|7)\.0(\.\d+|) safari/i.test( userAgent ) ) {
 		expected = {
-			"ajax": true,
 			"boxSizingReliable": true,
 			"checkClone": true,
 			"checkOn": true,
@@ -140,7 +135,6 @@ testIframeWithCallback( "Check CSP (https://developer.mozilla.org/en-US/docs/Sec
 		};
 	} else if ( /firefox/i.test( userAgent ) ) {
 		expected = {
-			"ajax": true,
 			"boxSizingReliable": true,
 			"checkClone": true,
 			"checkOn": true,
@@ -157,7 +151,6 @@ testIframeWithCallback( "Check CSP (https://developer.mozilla.org/en-US/docs/Sec
 		};
 	} else if ( /iphone os 8/i.test( userAgent ) ) {
 		expected = {
-			"ajax": true,
 			"boxSizingReliable": true,
 			"checkClone": true,
 			"checkOn": true,
@@ -174,7 +167,6 @@ testIframeWithCallback( "Check CSP (https://developer.mozilla.org/en-US/docs/Sec
 		};
 	} else if ( /iphone os (6|7)/i.test( userAgent ) ) {
 		expected = {
-			"ajax": true,
 			"boxSizingReliable": true,
 			"checkClone": true,
 			"checkOn": true,
@@ -191,7 +183,6 @@ testIframeWithCallback( "Check CSP (https://developer.mozilla.org/en-US/docs/Sec
 		};
 	} else if ( /android 4\.[0-3]/i.test( userAgent ) ) {
 		expected = {
-			"ajax": true,
 			"boxSizingReliable": true,
 			"checkClone": false,
 			"checkOn": false,
@@ -208,7 +199,6 @@ testIframeWithCallback( "Check CSP (https://developer.mozilla.org/en-US/docs/Sec
 		};
 	} else if ( /android 2\.3/i.test( userAgent ) ) {
 		expected = {
-			"ajax": true,
 			"boxSizingReliable": true,
 			"checkClone": true,
 			"checkOn": false,
@@ -238,7 +228,7 @@ testIframeWithCallback( "Check CSP (https://developer.mozilla.org/en-US/docs/Sec
 
 			for ( i in expected ) {
 				// TODO check for all modules containing support properties
-				if ( jQuery.ajax || i !== "ajax" && i !== "cors" ) {
+				if ( jQuery.ajax || i !== "cors" ) {
 					equal( computedSupport[ i ], expected[ i ],
 						"jQuery.support['" + i + "']: " + computedSupport[ i ] +
 							", expected['" + i + "']: " + expected[ i ]);