1.判断普通匿名函数

   var obj1 = Object.prototype.toString.call( function(){});
   console.log(obj1);
   console.log(obj1 === '[object Function]');

2.判断异步函数

   var obj2 = Object.prototype.toString.call( async function(){});
   console.log(obj2);
   console.log(obj2 === '[object AsyncFunction]');

 3.判断有名函数

   var obj3 = Object.prototype.toString.call( function *(){});
   console.log(obj3);
   console.log(obj3 === '[object GeneratorFunction]');