JS类型检测

1. typeof 操作符(适合基本类型及function检测，遇到null失效)

typeof 100-->"number"typeof true --> "boolean"typeof function --> "function"typeof(undefined)--> "undefined"typeof new Object--> "object"typeof [1,2] --> "object"typeof NaN --> "number"typeof null --> "object" ?

2. instanceof（基于原型链，适合自定义对象，也可以用来检测原生对象，在不同的iframe和window间检测时失效）

[1,2] instanceof Array === truenew Object() instanceof Array === false

3. Object.prototype.toString（适合内置对象和基本类型，遇到null和undefined失效，ie678返回[Object Object]）

Object.prototype.toString.apply([]) === "[Object Array]"Object.prototype.toString.apply(function(){}) === "[Object Function]"Object.prototype.toString.apply(null) === "[Object Null]" ==> ie6/7/8返回"[Object Object]"Object.prototype.toString.apply(undefined) === "[Object Undefined]"

4. constructor属性
5. duck type