isGeneratorFunction

Checks if the given argument is a generator function.

• Use Object.prototype.toString() and Function.prototype.call() and check if the result is '[object GeneratorFunction]'.

const isGeneratorFunction = val =>
  Object.prototype.toString.call(val) === '[object GeneratorFunction]';

isGeneratorFunction(function() {}); // false
isGeneratorFunction(function*() {}); // true