Hello， I run following code in lastest JavascriptCore, the result is wrong. TypeError should be thrown when returns duplicate entries. var proxy = new Proxy({}, { ownKeys: function(target) { print("in ownKeys"); return ['a','b','a']; }, }); print(Reflect.ownKeys(proxy)); print("BT_FLAG"); SpiderMonkey and V8 throw a TypeError: 'ownKeys' on proxy: trap returned duplicate entries, However, JavascriptCore execute without failures. BT group 2019.3.8