LibJS: Disallow static methods named prototype in classes

Author: https://github.com/davidot
Commit: 93b57e6d8c
Pull-request: https://github.com/SerenityOS/serenity/pull/8667
Reviewed-by: https://github.com/IdanHo
Reviewed-by: https://github.com/linusg

Userland/Libraries/LibJS/Parser.cpp

@@ -674,6 +674,12 @@ NonnullRefPtr<ClassExpression> Parser::parse_class_expression(bool expect_class_
                     break;
                 }
 
+                //https://tc39.es/ecma262/#sec-class-definitions-static-semantics-early-errors
+                // ClassElement : static MethodDefinition
+                //   It is a Syntax Error if PropName of MethodDefinition is "prototype".
+                if (is_static && name == "prototype"sv)
+                    syntax_error("Classes may not have a static property named 'prototype'");
+
             } else {
                 expected("property key");
             }