Core: Make jQuery objects iterable

Make iterating over jQuery objects possible using ES 2015 for-of:

    for ( node of $( "<div id=narwhal>" ) ) {
        console.log( node.id ); // "narwhal"
    }

(partially cherry-picked from bb026fc12c)

Fixes gh-1693

src/core.js

@@ -477,6 +477,16 @@ jQuery.extend({
 	support: support
 });
 
+// JSHint would error on this code due to the Symbol not being defined in ES5.
+// Defining this global in .jshintrc would create a danger of using the global
+// unguarded in another place, it seems safer to just disable JSHint for these
+// three lines.
+/* jshint ignore: start */
+if ( typeof Symbol === "function" ) {
+	jQuery.fn[ Symbol.iterator ] = deletedIds[ Symbol.iterator ];
+}
+/* jshint ignore: end */
+
 // Populate the class2type map
 jQuery.each("Boolean Number String Function Array Date RegExp Object Error".split(" "),
 function(i, name) {

test/.jshintrc

@@ -24,6 +24,7 @@
 		"DOMParser": false,
 		"JSON": false,
 		"Promise": false,
+		"Symbol": false,
 		"QUnit": false,
 		"ok": false,
 		"equal": false,

test/unit/core.js

@@ -1519,3 +1519,23 @@ testIframeWithCallback( "Don't call window.onready (#14802)", "core/onready.html
 			equal( error, false, "no call to user-defined onready" );
 	}
 );
+
+test( "Iterability of jQuery objects (gh-1693)", function() {
+	/* jshint unused: false */
+	expect( 1 );
+
+	var i, elem, result;
+
+	if ( typeof Symbol === "function" ) {
+
+		elem = jQuery( "<div></div><span></span><a></a>" );
+		result = "";
+
+		try {
+			eval( "for ( i of elem ) { result += i.nodeName; }" );
+		} catch ( e ) {}
+		equal( result, "DIVSPANA", "for-of works on jQuery objects" );
+	} else {
+		ok( true, "The browser doesn't support Symbols" );
+	}
+} );