CSS: Warn and fill access to jQuery.cssProps

Fixes jquery#283

Author: dmethvin

src/.eslintrc.json

@@ -11,6 +11,8 @@
 	},
 	"globals": {
 		"window": true,
+		"Proxy": true,
+		"Reflect": true,
 
 		"define": true,
 		"module": true,

src/css.js

@@ -42,3 +42,13 @@ jQuery.swap = function( elem, options, callback, args ) {
 
 	return ret;
 };
+
+if ( jQueryVersionSince( "3.4.0" ) && typeof Proxy !== "undefined" ) {
+
+	jQuery.cssProps = new Proxy( jQuery.cssProps || {}, {
+		set: function() {
+			migrateWarn( "JQMIGRATE: jQuery.cssProps is deprecated" );
+			return Reflect.set.apply( this, arguments );
+		}
+	} );
+}

test/css.js

@@ -25,3 +25,19 @@ QUnit.test( "jQuery.swap()", function( assert ) {
 	} );
 
 } );
+
+QUnit[ ( jQueryVersionSince( "3.4.0" ) && typeof Proxy !== "undefined" ) ? "test" : "skip" ]
+		( "jQuery.cssProps", function( assert ) {
+	assert.expect( 2 );
+
+	expectWarning( assert, "Write to cssProps", function() {
+		jQuery.cssProps.devoHat = "awesomeHat";
+	} );
+
+	expectNoWarning( assert, "Read from cssProps", function() {
+		jQuery.cssProps.devoHat;
+		jQuery.cssProps.unknownProp;
+	} );
+
+	delete jQuery.cssProps.devoHat;
+} );

warnings.md

@@ -235,3 +235,9 @@ See jQuery-ui [commit](https://github.com/jquery/jquery-ui/commit/c0093b599fcd58
 **Cause:** This public but never-documented method has been deprecated as of jQuery 3.2.0.
 
 **Solution:** Replace calls such as `jQuery.nodeName( elem, "div" )` with a test such as `elem.nodeName.toLowerCase() === "div"`.
+
+### JQMIGRATE: jQuery.cssProps is deprecated
+
+**Cause:** The `jQuery.cssProps` property is a public but undocumented object that allows CSS properties with one name to be mapped into another name. It was used for legacy browsers like IE8 that used non-standard names. This object is no longer used inside jQuery since all supported browsers now use the standard CSS property names.
+
+**Solution:** Remove any uses of `jQuery.cssProps` in application code.