判断用到的例子
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.最常见的方法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返回的类型都是字符串形式，需注意，例如：
alert(typeof a === "string") -------------> true
alert(typeof a === String) ---------------> false
2.判断已知对象类型的方法： instanceof
alert(c instanceof Array) ---------------> true
alert(d instanceof Date) ---------------> true
alert(f instanceof Function) ------------> true
alert(f instanceof function) ------------> false
3.根据对象的constructor判断： constructor
alert(c.constructor === Array) ----------> true
alert(d.constructor === Date) -----------> true
alert(e.constructor === Function) -------> true
4.考虑兼容，使用Object.prototype.toString.call(x)可以判断
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;
