//haorooms是全局变量
if(haorooms!=undefined){
}//js会报错，说"Uncaught ReferenceError: haorooms is not defined"

 if(typeof haorooms!=undefined){
 }

var haorooms="string"; console.log(haorooms); //string
var haorooms=1; console.log(haorooms); //number
var haorooms=false; console.log(haorooms); //boolean
var haorooms; console.log(typeof haorooms); //undfined

var haorooms= null; console.log(typeof haorooms); //object
var haorooms = document; console.log(typeof haorooms); //object
var haorooms = []; console.log(haorooms); //object
var haorooms = function(){}; console.log(typeof haorooms) //function  除了可以判断数据类型还可以判断function类型

var haorooms=[];
console.log(haorooms instanceof Array) //返回true 

console.log([].constructor == Array);
console.log({}.constructor == Object);
console.log("string".constructor == String);
console.log((123).constructor == Number);
console.log(true.constructor == Boolean);

function employee(name,job,born){
  this.name=name;
  this.job=job;
  this.born=born; }

var haorooms=new employee("Bill Gates","Engineer",1985); 
console.log(haorooms.constructor); //输出function employee(name, jobtitle, born){this.name = name; this.jobtitle = job; this.born = born;}

Object.prototype.toString.apply({}) // "[object Object]"
Object.prototype.toString.apply([]) // "[object Array]"
Object.prototype.toString.apply(NaN)// "[object Number]"
Object.prototype.toString.apply(function(){}) // "[object Function]"

$.isWindow(window) // true

core.js#479
isWindow: function( obj ) {
  return obj != null && obj == obj.window;
}

var fakeWindow;
fakeWindow = {};
fakeWindow.window = fakeWindow;
$.isWindow(fakeWindow) // true