Core: Support Symbol wrapper objects in jQuery.type

In ECMAScript 2015 (ES6), the native typeof operator returns "symbol"
for Symbol primitives. As it is possible to wrap symbols using the
Object constructor, symbols can be objects as well as any other
primitive type in JavaScript and should be determined by jQuery.type.

Cherry-picked from 8a734344f2
Closes gh-2627

src/core.js

@@ -498,7 +498,7 @@ if ( typeof Symbol === "function" ) {
 /* jshint ignore: end */
 
 // Populate the class2type map
-jQuery.each( "Boolean Number String Function Array Date RegExp Object Error".split( " " ),
+jQuery.each( "Boolean Number String Function Array Date RegExp Object Error Symbol".split( " " ),
 function( i, name ) {
 	class2type[ "[object " + name + "]" ] = name.toLowerCase();
 } );

test/unit/core.js

@@ -264,6 +264,19 @@ QUnit.test( "type", function( assert ) {
 	assert.equal( jQuery.type( new MyObject() ), "object", "Object" );
 } );
 
+QUnit.test( "type for `Symbol`", function( assert ) {
+	// Prevent reference errors
+	if( typeof Symbol !== "function" ) {
+		assert.expect( 0 );
+		return
+	}
+
+	assert.expect( 2 );
+
+	assert.equal( jQuery.type( Symbol() ), "symbol", "Symbol" );
+	assert.equal( jQuery.type( Object( Symbol() ) ), "symbol", "Symbol" );
+});
+
 QUnit.asyncTest( "isPlainObject", function( assert ) {
 	assert.expect( 16 );