Core: Fill in & warn against jQuery.proxy

Fixes jquerygh-460

src/jquery/core.js

@@ -8,6 +8,8 @@ import {
 import "../disablePatches.js";
 
 var findProp,
+	arr = [],
+	slice = arr.slice,
 	class2type = {},
 	oldInit = jQuery.fn.init,
 	oldFind = jQuery.find,
@@ -176,4 +178,39 @@ if ( jQueryVersionSince( "3.3.0" ) ) {
 		}, "isWindow",
 		"jQuery.isWindow() is deprecated"
 	);
+
+	// Bind a function to a context, optionally partially applying any
+	// arguments.
+	// jQuery.proxy is deprecated to promote standards (specifically Function#bind)
+	// However, it is not slated for removal any time soon
+	migratePatchAndWarnFunc( jQuery, "proxy",
+		function( fn, context ) {
+			var tmp, args, proxy;
+
+			if ( typeof context === "string" ) {
+				tmp = fn[ context ];
+				context = fn;
+				fn = tmp;
+			}
+
+			// Quick check to determine if target is callable, in the spec
+			// this throws a TypeError, but we will just return undefined.
+			if ( typeof fn !== "function" ) {
+				return undefined;
+			}
+
+			// Simulated bind
+			args = slice.call( arguments, 2 );
+			proxy = function() {
+				return fn.apply( context || this, args.concat( slice.call( arguments ) ) );
+			};
+
+			// Set the guid of unique handler to the same of original handler, so it can be removed
+			proxy.guid = fn.guid = fn.guid || jQuery.guid++;
+
+			return proxy;
+		}, "proxy",
+		"jQuery.proxy() is deprecated"
+	);
+
 }

test/unit/jquery/core.js

@@ -449,3 +449,59 @@ TestManager.runIframeTest( "old pre-3.0 jQuery", "core-jquery2.html",
 
 		assert.ok( /jQuery 3/.test( log ), "logged: " + log );
 } );
+
+QUnit[ jQueryVersionSince( "3.3.0" ) ? "test" : "skip" ]( "jQuery.proxy", function( assert ) {
+	assert.expect( 10 );
+
+	var test2, test3, test4, fn, cb,
+		test = function() {
+			assert.equal( this, thisObject, "Make sure that scope is set properly." );
+		},
+		thisObject = { foo: "bar", method: test };
+
+	expectWarning( assert, "jQuery.proxy", 7, function() {
+
+		// Make sure normal works
+		test.call( thisObject );
+
+		// Basic scoping
+		jQuery.proxy( test, thisObject )();
+
+		// Another take on it
+		jQuery.proxy( thisObject, "method" )();
+
+		// Make sure it doesn't freak out
+		assert.equal( jQuery.proxy( null, thisObject ), undefined,
+			"Make sure no function was returned." );
+
+		// Partial application
+		test2 = function( a ) {
+			assert.equal( a, "pre-applied", "Ensure arguments can be pre-applied." );
+		};
+		jQuery.proxy( test2, null, "pre-applied" )();
+
+		// Partial application w/ normal arguments
+		test3 = function( a, b ) {
+			assert.equal( b, "normal", "Ensure arguments can be pre-applied and passed as usual." );
+		};
+		jQuery.proxy( test3, null, "pre-applied" )( "normal" );
+
+		// Test old syntax
+		test4 = {
+			"meth": function( a ) {
+				assert.equal( a, "boom", "Ensure old syntax works." );
+			}
+		};
+		jQuery.proxy( test4, "meth" )( "boom" );
+
+		// jQuery 1.9 improved currying with `this` object
+		fn = function() {
+			assert.equal( Array.prototype.join.call( arguments, "," ),
+				"arg1,arg2,arg3",
+				"args passed" );
+			assert.equal( this.foo, "bar", "this-object passed" );
+		};
+		cb = jQuery.proxy( fn, null, "arg1", "arg2" );
+		cb.call( thisObject, "arg3" );
+	} );
+} );

warnings.md

@@ -229,6 +229,12 @@ See jQuery-ui [commit](https://github.com/jquery/jquery-ui/commit/c0093b599fcd58
 
 **Solution:** Remove any use of `jQuery.isWindow()` from code. If it is truly needed it can be replaced with a check for `obj != null && obj === obj.window` which was the test used inside this method.
 
+### \[proxy\] JQMIGRATE: jQuery.proxy() is deprecated
+
+**Cause:** `jQuery.proxy` is similar to `Function.prototype.bind`; the main difference is it preserves function identity perceived by jQuery. The most common usage of that is in event handlers - you can unbind a proxied function by passing the original one. Because of the similarity to native `bind`, `jQuery.proxy` has been deprecated in jQuery 3.3.0.
+
+**Solution:** Replace any use of `jQuery.proxy()` with function `.bind()`. If a proxied function is passed as a jQuery event handler, make sure to pass the same bounded function to `.off()`.
+
 ### \[shorthand-deprecated-v3\] JQMIGRATE: jQuery.fn.click() event shorthand is deprecated
 
 **Cause:** The `.on()` and `.trigger()` methods can set an event handler or generate an event for any event type, and should be used instead of the shortcut methods. This message also applies to the other event shorthands, including: blur, focus, focusin, focusout, resize, scroll, dblclick, mousedown, mouseup, mousemove, mouseover, mouseout, mouseenter, mouseleave, change, select, submit, keydown, keypress, keyup, and contextmenu.