Core: Warn and fill jQuery.isWindow

Fixes jquery#263
Closes jquery#290

src/core.js

@@ -89,6 +89,15 @@ jQuery.isNumeric = function( val ) {
 	return oldValue;
 };
 
+if ( jQueryVersionSince( "3.3.0" ) ) {
+	migrateWarnFunc( jQuery, "isWindow",
+		function( obj ) {
+			return obj != null && obj === obj.window;
+		},
+		"jQuery.isWindow() is deprecated"
+	);
+}
+
 migrateWarnFunc( jQuery, "holdReady", jQuery.holdReady,
 	"jQuery.holdReady is deprecated" );
 

test/core.js

@@ -250,6 +250,15 @@ QUnit.test( "jQuery.isNumeric", function( assert ) {
 	} );
 } );
 
+QUnit[ jQueryVersionSince( "3.3.0" ) ? "test" : "skip" ]( "jQuery.isWindow", function( assert ) {
+	assert.expect( 3 );
+
+	expectWarning( assert, "isWindow", 1, function() {
+		assert.equal( jQuery.isWindow( [] ), false, "array" );
+		assert.equal( jQuery.isWindow( window ), true, "window" );
+	} );
+} );
+
 QUnit.test( "jQuery.unique", function( assert ) {
 	assert.expect( 2 );
 

warnings.md

@@ -206,6 +206,11 @@ See jQuery-ui [commit](https://github.com/jquery/jquery-ui/commit/c0093b599fcd58
 
 **Solution:** Rewrite the page so that it does not require all jQuery ready handlers to be delayed. This might be accomplished, for example, by late-loading only the code that requires the delay when it is safe to run. Due to the complexity of this method, jQuery Migrate does not attempt to fill the functionality. If the underlying version of jQuery used with jQuery Migrate no longer contains `jQuery.holdReady()` the code will fail shortly after this warning appears.
 
+### JQMIGRATE: jQuery.isWindow() is deprecated
+
+**Cause:** This method returns `true` if its argument is thought to be a `window` element. It was created for internal use and is not a reliable way of detecting `window` for public needs.
+
+**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.
 
 ### JQMIGRATE: jQuery.fn.click() event shorthand is deprecated