/**  *  * js的类型检测方式->typeof、constuctor。  * 推荐通过构造函数来检测变量的类型。  */  var obj = {key:'value'},          arr = ["hello","javascript"],          fn  = function(){},          str = "hello js",          num = 55,          bool = true,          User = function(){},          user = new User();      /*typeof测试*/      console.log(typeof obj);    //obj      console.log(typeof arr);    //obj      console.log(typeof fn);     //function      console.log(typeof str);    //string      console.log(typeof num);    //number      console.log(typeof bool);   //boolean      console.log(typeof user);   //object      /*constructor测试*/      console.log(obj.constructor == Object); //true      console.log(arr.constructor == Array);  //true      console.log(str.constructor == String); //true      console.log(num.constructor == Number); //true      console.log(bool.constructor == Boolean);//true      console.log(user.constructor == User);  //true