Fixes #13815: Ensure each element has its own private data object - Tests by @rwldrn

src/data.js

@@ -90,13 +90,9 @@ Data.prototype = {
 
 		// Handle: [ owner, { properties } ] args
 		} else {
-			// Support an expectation from the old data system where plain
-			// objects used to initialize would be set to the cache by
-			// reference, instead of having properties and values copied.
-			// Note, this will kill the connection between
-			// "this.cache[ unlock ]" and "cache"
+			// Fresh assignments by object are shallow copied
 			if ( jQuery.isEmptyObject( cache ) ) {
-				this.cache[ unlock ] = data;
+				jQuery.extend( this.cache[ unlock ], data );
 			// Otherwise, copy the properties one-by-one to the cache object
 			} else {
 				for ( prop in data ) {
@@ -104,6 +100,7 @@ Data.prototype = {
 				}
 			}
 		}
+		return cache;
 	},
 	get: function( owner, key ) {
 		// Either a valid cache is found, or will be created.

src/manipulation.js

@@ -527,11 +527,9 @@ function cloneCopyEvent( src, dest ) {
 	// 1. Copy private data: events, handlers, etc.
 	if ( data_priv.hasData( src ) ) {
 		pdataOld = data_priv.access( src );
-		pdataCur = jQuery.extend( {}, pdataOld );
+		pdataCur = data_priv.set( dest, pdataOld );
 		events = pdataOld.events;
 
-		data_priv.set( dest, pdataCur );
-
 		if ( events ) {
 			delete pdataCur.handle;
 			pdataCur.events = {};

test/unit/data.js

@@ -244,6 +244,18 @@ test("jQuery(plain Object).data(String, Object).data(String)", function() {
 	deepEqual( $obj[0], { exists: true }, "removeData does not clear the object" );
 });
 
+test(".data(object) does not retain references. #13815", function() {
+	expect( 2 );
+
+	var $divs = jQuery("<div></div><div></div>").appendTo("#qunit-fixture");
+
+	$divs.data({ "type": "foo" });
+	$divs.eq( 0 ).data( "type", "bar" );
+
+	equal( $divs.eq( 0 ).data("type"), "bar", "Correct updated value" );
+	equal( $divs.eq( 1 ).data("type"), "foo", "Original value retained" );
+});
+
 test("data-* attributes", function() {
 	expect(40);
 	var prop, i, l, metadata, elem,