typeof

var myFun=function(){};
var myObj={};
var myStr="str";
var myNum=1;
var myArr=[1,2,3];
var myNull=null;
var myUndefined=undefined;

typeof myFun;  //Function
typeof myObj;  //Object
typeof myStr;   //String
typeof myNum; //number
typeof myArr;   //Object
typeof myNull; //object
typeof myUndefined;   //undefined