check if function is a generator

Question

I played with generators in Nodejs v0.11.2 and I\'m wondering how I can check that argument to my function is generator function.

I found this way typeof f ===

Answer 1

As @Erik Arvidsson stated, there is no standard-way to check if a function is a generator function. But you can, for sure, just check for the interface, a generator function fulfills:

function* fibonacci(prevPrev, prev) {

  while (true) {

    let next = prevPrev + prev;

    yield next;

    prevPrev = prev;
    prev = next;
  }
}

// fetch get an instance
let fibonacciGenerator = fibonacci(2, 3)

// check the interface
if (typeof fibonacciGenerator[Symbol.iterator] == 'function' && 
    typeof fibonacciGenerator['next'] == 'function' &&
    typeof fibonacciGenerator['throw'] == 'function') {

  // it's safe to assume the function is a generator function or a shim that behaves like a generator function

  let nextValue = fibonacciGenerator.next().value; // 5
}

Thats's it.