js检测数据类型

1.基本数据类型：String、Number、Boolean、undefined、null
2.引用数据类型：Object、Array、Date、RegExp、Function

检测基本类型用typeof
检测引用类型用instanceof

var u;
typeof "hello world";     //string
typeof 22;                    //number
typeof true;                  //boolean
typeof u;                      //undefined
typeof null;                  //object

引用类型用typeof都是object

var now = new Date();
var x = {};
var y = function(){};
now instanceof Date;       //true
[] instanceof Array;         //true
x instanceof Object        //true 
y instanceof Function     // true