AsyncFunction and GeneratorFunction issues

I think, tests should pass:

const type = require('type-detect');
const assert = require('assert');

const asyncFn = async () => {};
const generatorFn = function* generator () {};

function getTag(obj) {
  return Object.prototype.toString.call(obj).slice(8, -1);
}

assert(type(asyncFn) === getTag(asyncFn));
assert(type(generatorFn) === getTag(generatorFn));

Is it a bug? If not, you should add it to README.

[keithamus]

Hey @doasync thanks for the issue

This, again, is because of the early typeof optimisation; async () = >{} and function *() {} are all typeof x === "function", and so we return that early:

https://github.com/chaijs/type-detect/blob/c7895e499ecc0a93c567adef9fa2b33eec13d2ab/index.js#L54-L57

We could probably change that to:

  var typeofObj = typeof obj;
  if (typeofObj !== 'object' && typeofObj !== 'function') {
    return typeofObj;
  }

We’d welcome a PR, which includes that change plus you’ll need to change the tests for generatorfunction, which are here: https://github.com/chaijs/type-detect/blob/c7895e499ecc0a93c567adef9fa2b33eec13d2ab/test/new-ecmascript-types.js#L129-L135

Also, on top of that, this lib does not have tests for async functions as they weren’t around when the lib was written - so you’ll need to add tests for that.

[keithamus]

I would argue that type-detects role is really a fancy polyfill for @@toStringTag. Almost all of the code that isn’t returning just [Symbol.toStringTag] is for performance or for conformance - arguably that includes the typeof check at the beginning. Framed this way, it seems to make a lot more sense for type-detect to distinguish between different types of functions.