Object.prototype.toString.call（obj）

<script type="text/javascript">
        var arr=[1,2,3];
        var obj=new Object();
        var str="hello";
        console.log(Object.prototype.toString.call(arr));
        console.log(Object.prototype.toString.call(obj));
        console.log(Object.prototype.toString.call(str));
        console.log(arr.toString());
        /*
          [object Array]
          [object Object]
          [object String]
          1,2,3
        */
    </script>

typeof arr;
A instanceof B;
a.constructor=A;

https://www.cnblogs.com/youhong/p/6209054.html