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 === 'function' && Object.getPrototypeOf(f) !== Object.getPrototypeOf(Function) but I'm not sure if this is good (and working in future) way.

What is your opinion about this issue?

Answer 1

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)

Answer 2

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'; }