判斷用到的例子

var a = "iamstring.";
var b = 222;
var c= [1,2,3];
var d = new Date();
var e = function(){alert(111);};
var f = function(){this.name="22";};

1.最常見的方法typeof

alert(typeof a)   ------------> string
alert(typeof b)   ------------> number
alert(typeof c)   ------------> object
alert(typeof d)   ------------> object
alert(typeof e)   ------------> function
alert(typeof f)   ------------> function

其中typeof返回的類型都是字符串形式，需注意，例如：
alert(typeof a === "string") -------------> true
alert(typeof a === String) ---------------> false

2.判斷已知對(duì)象類型的方法： instanceof

alert(c instanceof Array) ---------------> true
alert(d instanceof Date)  ---------------> true
alert(f instanceof Function) ------------> true
alert(f instanceof function) ------------> false

3.根據(jù)對(duì)象的constructor判斷： constructor

alert(c.constructor === Array) ----------> true
alert(d.constructor === Date) -----------> true
alert(e.constructor === Function) -------> true

4.考慮兼容，使用Object.prototype.toString.call(x)可以判斷

alert(Object.prototype.toString.call(a) === ‘[object String]’) -------> true;
alert(Object.prototype.toString.call(b) === ‘[object Number]’) -------> true;
alert(Object.prototype.toString.call(c) === ‘[object Array]’) -------> true;
alert(Object.prototype.toString.call(d) === ‘[object Date]’) -------> true;
alert(Object.prototype.toString.call(e) === ‘[object Function]’) -------> true;
alert(Object.prototype.toString.call(f) === ‘[object Function]’) -------> true;

內(nèi)容來自參考文：https://www.cnblogs.com/dushao/p/5999563.html