Data: Patch & warn about props from Object.prototype in data objects

src/jquery/data.js

@@ -0,0 +1,86 @@
+import { migratePatchFunc, migrateWarn } from "../main.js";
+
+function patchDataProto( original, options ) {
+	var i,
+		apiName = options.apiName,
+		isInstanceMethod = options.isInstanceMethod,
+
+		// `Object.prototype` keys are not enumerable so list the
+		// official ones here. An alternative would be wrapping
+		// data objects with a Proxy but that creates additional issues
+		// like breaking object identity on subsequent calls.
+		objProtoKeys = [
+			"__proto__",
+			"__defineGetter__",
+			"__defineSetter__",
+			"__lookupGetter__",
+			"__lookupSetter__",
+			"hasOwnProperty",
+			"isPrototypeOf",
+			"propertyIsEnumerable",
+			"toLocaleString",
+			"toString",
+			"valueOf"
+		],
+
+		// Use a null prototype at the beginning so that we can define our
+		// `__proto__` getter & setter. We'll reset the prototype afterwards.
+		intermediateDataObj = Object.create( null );
+
+	for ( i = 0; i < objProtoKeys.length; i++ ) {
+		( function( key ) {
+			Object.defineProperty( intermediateDataObj, key, {
+				get: function() {
+					migrateWarn( "data-null-proto",
+						"Accessing properties from " + apiName +
+						" inherited from Object.prototype is removed" );
+					return ( key + "__cache" ) in intermediateDataObj ?
+						intermediateDataObj[ key + "__cache" ] :
+						Object.prototype[ key ];
+				},
+				set: function( value ) {
+					migrateWarn( "data-null-proto",
+						"Setting properties from " + apiName +
+						" inherited from Object.prototype is removed" );
+					intermediateDataObj[ key + "__cache" ] = value;
+				}
+			} );
+		} )( objProtoKeys[ i ] );
+	}
+
+	Object.setPrototypeOf( intermediateDataObj, Object.prototype );
+
+	return function jQueryDataProtoPatched() {
+		var result = original.apply( this, arguments );
+
+		if ( arguments.length !== ( isInstanceMethod ? 0 : 1 ) || result === undefined ) {
+			return result;
+		}
+
+		// Insert an additional object in the prototype chain between `result`
+		// and `Object.prototype`; that intermediate object proxies properties
+		// to `Object.prototype`, warning about their usage first.
+		Object.setPrototypeOf( result, intermediateDataObj );
+
+		return result;
+	};
+}
+
+// Yes, we are patching jQuery.data twice; here & above. This is necessary
+// so that each of the two patches can be independently disabled.
+migratePatchFunc( jQuery, "data",
+	patchDataProto( jQuery.data, {
+		apiName: "jQuery.data()",
+		isPrivateData: false,
+		isInstanceMethod: false
+	} ),
+	"data-null-proto" );
+migratePatchFunc( jQuery.fn, "data",
+	patchDataProto( jQuery.fn.data, {
+		apiName: "jQuery.fn.data()",
+		isPrivateData: true,
+		isInstanceMethod: true
+	} ),
+	"data-null-proto" );
+
+// TODO entry in warnings.md

src/migrate.js

@@ -6,6 +6,7 @@ import "./jquery/selector.js";
 import "./jquery/ajax.js";
 import "./jquery/attributes.js";
 import "./jquery/css.js";
+import "./jquery/data.js";
 import "./jquery/effects.js";
 import "./jquery/event.js";
 import "./jquery/manipulation.js";

test/data/testinit.js

@@ -62,6 +62,7 @@
 				"unit/jquery/ajax.js",
 				"unit/jquery/attributes.js",
 				"unit/jquery/css.js",
+				"unit/jquery/data.js",
 				"unit/jquery/deferred.js",
 				"unit/jquery/effects.js",
 				"unit/jquery/event.js",

test/unit/jquery/data.js

@@ -0,0 +1,21 @@
+QUnit.module( "data" );
+
+QUnit.test( "properties from Object.prototype", function( assert ) {
+	assert.expect( 6 );
+
+	var div = jQuery( "<div>" ).appendTo( "#qunit-fixture" );
+
+	div.data( "foo", "bar" );
+
+	expectNoMessage( assert, "Regular properties", function() {
+		assert.strictEqual( div.data( "foo" ), "bar", "data access" );
+		assert.strictEqual( jQuery.data( div[ 0 ], "foo" ), "bar", "data access (static method)" );
+	} );
+
+	expectMessage( assert, "Properties from Object.prototype", 2, function() {
+		assert.ok( div.data().hasOwnProperty( "foo" ),
+			"hasOwnProperty works" );
+		assert.ok( jQuery.data( div[ 0 ] ).hasOwnProperty( "foo" ),
+			"hasOwnProperty works (static method)" );
+	} );
+} );

warnings.md

@@ -144,6 +144,15 @@ This is _not_ a warning, but a console log message the plugin shows when it firs
 
 **Solution:** Always pass string values to `.css()`, and explicitly add units where required. For example, use `$.css("line-height", "2")` to specify 200% of the current line height or `$.css("line-height", "2px")` to specify pixels. When the numeric value is in a variable, ensure the value is converted to string, e.g. `$.css("line-height", String(height))` and `$.css("line-height", height+"px")`.
 
+### \[data-null-proto\] Accessing properties from jQuery.data() inherited from Object.prototype is removed
+### \[data-null-proto\] Setting properties from jQuery.data() inherited from Object.prototype is removed
+### \[data-null-proto\] Accessing properties from jQuery.fn.data() inherited from Object.prototype is removed
+### \[data-null-proto\] Setting properties from jQuery.fn.data() inherited from Object.prototype is removed
+
+**Cause:** As of jQuery 4.0.0, data objects no longer inherit from `Object.prototype`. This includes properties like `__proto__` or `hasOwnProperty`.
+
+**Solution:** Don't use properties inherited from `Object.prototype` on data objects. Instead of `jQuery.data( node ).hasOwnProperty( "foo" )` use `Object.hasOwn( jQuery.data( node ), "foo" )` or, if you need to support older browsers like IE 11, use `Object.prototype.hasOwnProperty.call( jQuery.data( node ), "foo" )`.
+
 ### \[self-closed-tags\] JQMIGRATE: HTML tags must be properly nested and closed: _(HTML string)_
 
 **Cause:** jQuery 3.5.0 changed the way it processes HTML strings. Previously, jQuery would attempt to fix self-closed tags like `<i class="test" />` that the HTML5 specification says are not self-closed, turning it into `<i class="test"></i>`. This processing can create a [security problem](https://nvd.nist.gov/vuln/detail/CVE-2020-11022) with malicious strings, so the functionality had to be removed.