check if function is a generator

In the latest version of nodejs (I verified with v0.11.12) you can check if the constructor name is equal to GeneratorFunction. I don't know what version this came out in but it works.

function isGenerator(fn) {
    return fn.constructor.name === 'GeneratorFunction';
}

We talked about this in the TC39 face-to-face meetings and it is deliberate that we don't expose a way to detect whether a function is a generator or not. The reason is that any function can return an iterable object so it does not matter if it is a function or a generator function.

var iterator = Symbol.iterator;

function notAGenerator() {
  var  count = 0;
  return {
    [iterator]: function() {
      return this;
    },
    next: function() {
      return {value: count++, done: false};
    }
  }
}

function* aGenerator() {
  var count = 0;
  while (true) {
    yield count++;
  }
}

These two behave identical (minus .throw() but that can be added too)