Reflect.js
function ToPropertyKey(argument) {
            var key = ToPrimitive(argument, 3 /* String */);
            if (IsSymbol(key))
                return key;
            return ToString(key);
        }
function ToPropertyKey(argument) {
            var key = ToPrimitive(argument, 3 /* String */);
            if (IsSymbol(key))
                return key;
            return ToString(key);
        }
7.1.14 ToPropertyKey(argument) https://tc39.github.io/ecma262/#sec-topropertykey