How to call a method of an object (especially a generator)?

[WhiredPlanck]

For example, a generator function like:

function* generator(i) {
    yield i
    yield i + 1
    yield i + 2
}

then eval on context to get Value instance in C++ ... :

Value generatorFunc = context.eval("generator");
Value generator = ((std::function<Value(int)>) generatorFunc)(10);

I've tried:

Value nextFunc = generator["next"];
Value result = ((std::function<Value(void)>) nextFunc)();

but got a TypeError: not a generator.