JavaScript ES6: Test for arrow function, built-in function, regular function?

Question

Is there an elegant way to tell Harmony\'s slim arrow functions apart from regular functions and built-in functions?

The Harmony wiki states that:

Answer 1

I wrote this for Node, should work in Chrome as well.

"Boundness" is detected (apparently, only on ES6) and reported as native && bound. This might or might not be an issue, depending on what you are using that information for.

const flags = {
  function: f instanceof Function,
  name: undefined,
  native: false,
  bound: false,
  plain: false,
  arrow: false
};

if (flags.function) {
  flags.name = f.name || '(anonymous)';
  flags.native = f.toString().trim().endsWith('() { [native code] }');
  flags.bound = flags.native && flags.name.startsWith('bound ');
  flags.plain = !flags.native && f.hasOwnProperty('prototype');
  flags.arrow = !(flags.native || flags.plain);
}

return flags;