Dan Tao Dan Tao - 2 months ago 15
Javascript Question

How to identify an ES6 generator

Say I've got a generator function like this:

var g = function*() {
yield 1;
yield 2;
yield 3;

var gen = g();

How can I tell programmatically that
is a generator function, or that
is an iterator?

This seems like one possibility:

g.constructor.name === 'GeneratorFunction'

Is there a better way?

Update: I ended up taking an approach similar to Eric's answer, but using
to first determine whether generators are supported on the target platform in the first place. Here is the implementation:

var GeneratorConstructor = (function() {
try {
var generator;
return eval('generator = function*() { yield 1; };').constructor;

} catch (e) {
// If the above throws a SyntaxError, that means generators aren't
// supported on the current platform, which means isGenerator should
// always return false. So we'll return an anonymous function here, so
// that instanceof checks will always return false.
return function() {};

* Checks whether a function is an ES6 Harmony generator.
* @private
* @param {Function} fn
* @returns {boolean}
function isGenerator(fn) {
return fn instanceof GeneratorConstructor;


Combining your solution with other solutions, this avoids the need for the global GeneratorFunction:

g instanceof (function*() {}).constructor