ES6中如何判断Set和Map等类型
怎么判断这些数据类型?
Chai 有过讨论，这个应该可以满足了
```
function getType(obj) {
     var type = Object.prototype.toString.call(obj).match(/^\[object (.*)\]$/)[1].toLowerCase();
     if(type === 'string' && typeof obj === 'object') return 'object'; // Let "new String('')" return 'object'
     if (obj === null) return 'null'; // PhantomJS has type "DOMWindow" for null
     if (obj === undefined) return 'undefined'; // PhantomJS has type "DOMWindow" for undefined
     return type;
   }
```
```
getType(new Map()) // "map"
```