Fixes #9887: ajax now supports circular references into objects passed as context. Prefilter and transport developpers should add their own custom option into flatOptions when needed. Unit test added.

src/ajax.js

@@ -135,6 +135,22 @@ function inspectPrefiltersOrTransports( structure, options, originalOptions, jqX
 	return selection;
 }
 
+// A special extend for ajax options
+// that takes "flat" options (not to be deep extended)
+// Fixes #9887
+function ajaxExtend( target, src ) {
+	var key, deep,
+		flatOptions = jQuery.ajaxSettings.flatOptions || {};
+	for( key in src ) {
+		if ( src[ key ] !== undefined ) {
+			( flatOptions[ key ] ? target : ( deep || ( deep = {} ) ) )[ key ] = src[ key ];
+		}
+	}
+	if ( deep ) {
+		jQuery.extend( true, target, deep );
+	}
+}
+
 jQuery.fn.extend({
 	load: function( url, params, callback ) {
 		if ( typeof url !== "string" && _load ) {
@@ -278,23 +294,16 @@ jQuery.extend({
 	// Creates a full fledged settings object into target
 	// with both ajaxSettings and settings fields.
 	// If target is omitted, writes into ajaxSettings.
-	ajaxSetup: function ( target, settings ) {
+	ajaxSetup: function( target, settings ) {
-		if ( !settings ) {
+		if ( settings ) {
-			// Only one parameter, we extend ajaxSettings
+			// Building a settings object
-			settings = target;
+			ajaxExtend( target, jQuery.ajaxSettings );
-			target = jQuery.extend( true, jQuery.ajaxSettings, settings );
 		} else {
-			// target was provided, we extend into it
+			// Extending ajaxSettings
-			jQuery.extend( true, target, jQuery.ajaxSettings, settings );
+			settings = target;
-		}
+			target = jQuery.ajaxSettings;
-		// Flatten fields we don't want deep extended
-		for( var field in { context: 1, url: 1 } ) {
-			if ( field in settings ) {
-				target[ field ] = settings[ field ];
-			} else if( field in jQuery.ajaxSettings ) {
-				target[ field ] = jQuery.ajaxSettings[ field ];
-			}
 		}
+		ajaxExtend( target, settings );
 		return target;
 	},
 
@@ -352,6 +361,15 @@ jQuery.extend({
 
 			// Parse text as xml
 			"text xml": jQuery.parseXML
+		},
+
+		// For options that shouldn't be deep extended:
+		// you can add your own custom options here if
+		// and when you create one that shouldn't be
+		// deep extended (see ajaxExtend)
+		flatOptions: {
+			context: true,
+			url: true
 		}
 	},
 
@@ -563,7 +581,7 @@ jQuery.extend({
 			completeDeferred.resolveWith( callbackContext, [ jqXHR, statusText ] );
 
 			if ( fireGlobals ) {
-				globalEventContext.trigger( "ajaxComplete", [ jqXHR, s] );
+				globalEventContext.trigger( "ajaxComplete", [ jqXHR, s ] );
 				// Handle the global AJAX counter
 				if ( !( --jQuery.active ) ) {
 					jQuery.event.trigger( "ajaxStop" );

test/unit/ajax.js

@@ -2076,6 +2076,22 @@ test( "jQuery.ajax - Location object as url (#7531)", 1, function () {
 	ok( success, "document.location did not generate exception" );
 });
 
+test( "jQuery.ajax - Context with circular references (#9887)", 2, function () {
+	var success = false,
+		context = {};
+	context.field = context;
+	try {
+		success = !jQuery.ajax( "non-existing", {
+			context: context,
+			beforeSend: function() {
+				ok( this === context, "context was not deep extended" );
+				return false;
+			}
+		});
+	} catch (e) { console.log( e ); }
+	ok( success, "context with circular reference did not generate an exception" );
+});
+
 test( "jQuery.ajax - statusCode" , function() {
 
 	var count = 12;