Object.prototype.toString.call

查了 ecmascript 262 spec 以及 ie6 ，firefox3.5 实验才发现实际和标准还是不完全一样的

利用 Object.prototype.toString.call 得到 [[class]]

IE6 6.0.2900.5512

Js代码

Object.prototype.toString.call(String.prototype) : [object Object]
Object.prototype.toString.call(Number.prototype) : [object Number]
Object.prototype.toString.call(undefined) : [object Object]
Object.prototype.toString.call(null) : [object Object]
Object.prototype.toString.call(Boolean.prototype) : [object Boolean]
Object.prototype.toString.call(Function.prototype) : [object Function]
Object.prototype.toString.call(Array.prototype) : [object Array]
Object.prototype.toString.call(Date.prototype) : [object Date]
Object.prototype.toString.call(RegExp.prototype) : [object RegExp]
Object.prototype.toString.call(Object.prototype) : [object Object]
Object.prototype.toString.call(Error.prototype) : [object Object]
Object.prototype.toString.call(EvalError.prototype) : [object Error]
Object.prototype.toString.call(Error) : [object Function]
Object.prototype.toString.call(EvalError) : [object Function]
Object.prototype.toString.call(/t/) : [object RegExp]

Object.prototype.toString.call(String.prototype) : [object Object]
Object.prototype.toString.call(Number.prototype) : [object Number]
Object.prototype.toString.call(undefined) : [object Object]
Object.prototype.toString.call(null) : [object Object]
Object.prototype.toString.call(Boolean.prototype) : [object Boolean]
Object.prototype.toString.call(Function.prototype) : [object Function]
Object.prototype.toString.call(Array.prototype) : [object Array]
Object.prototype.toString.call(Date.prototype) : [object Date]
Object.prototype.toString.call(RegExp.prototype) : [object RegExp]
Object.prototype.toString.call(Object.prototype) : [object Object]
Object.prototype.toString.call(Error.prototype) : [object Object]
Object.prototype.toString.call(EvalError.prototype) : [object Error]
Object.prototype.toString.call(Error) : [object Function]
Object.prototype.toString.call(EvalError) : [object Function]
Object.prototype.toString.call(/t/) : [object RegExp]

Firefox 3.5.2

Js代码

Object.prototype.toString.call(String.prototype) : [object String]
Object.prototype.toString.call(Number.prototype) : [object Number]
Object.prototype.toString.call(undefined) : [object Window]
Object.prototype.toString.call(null) : [object Window]
Object.prototype.toString.call(Boolean.prototype) : [object Boolean]
Object.prototype.toString.call(Function.prototype) : [object Function]
Object.prototype.toString.call(Array.prototype) : [object Array]
Object.prototype.toString.call(Date.prototype) : [object Date]
Object.prototype.toString.call(RegExp.prototype) : [object RegExp]
Object.prototype.toString.call(Object.prototype) : [object Object]
Object.prototype.toString.call(Error.prototype) : [object Error]
Object.prototype.toString.call(EvalError.prototype) : [object Error]
Object.prototype.toString.call(Error) : [object Function]
Object.prototype.toString.call(EvalError) : [object Function]
Object.prototype.toString.call(/t/) : [object RegExp]

Object.prototype.toString.call(String.prototype) : [object String]
Object.prototype.toString.call(Number.prototype) : [object Number]
Object.prototype.toString.call(undefined) : [object Window]
Object.prototype.toString.call(null) : [object Window]
Object.prototype.toString.call(Boolean.prototype) : [object Boolean]
Object.prototype.toString.call(Function.prototype) : [object Function]
Object.prototype.toString.call(Array.prototype) : [object Array]
Object.prototype.toString.call(Date.prototype) : [object Date]
Object.prototype.toString.call(RegExp.prototype) : [object RegExp]
Object.prototype.toString.call(Object.prototype) : [object Object]
Object.prototype.toString.call(Error.prototype) : [object Error]
Object.prototype.toString.call(EvalError.prototype) : [object Error]
Object.prototype.toString.call(Error) : [object Function]
Object.prototype.toString.call(EvalError) : [object Function]
Object.prototype.toString.call(/t/) : [object RegExp]

ecma 262 spec

Js代码

Object.prototype.toString.call(String.prototype) : [object String]
Object.prototype.toString.call(Number.prototype) : [object Number]
Object.prototype.toString.call(undefined) : global object implementation dependent
Object.prototype.toString.call(null) : global object implementation dependent
Object.prototype.toString.call(Boolean.prototype) : [object Boolean]
Object.prototype.toString.call(Function.prototype) : [object Function]
Object.prototype.toString.call(Array.prototype) : [object Array]
Object.prototype.toString.call(Date.prototype) : [object Date]
Object.prototype.toString.call(RegExp.prototype) : [object RegExp]
Object.prototype.toString.call(Object.prototype) : [object Object]
Object.prototype.toString.call(Error.prototype) : [object Error]
Object.prototype.toString.call(EvalError.prototype) : [object Error]
Object.prototype.toString.call(Error) : [object Function]
Object.prototype.toString.call(EvalError) : [object Function]
Object.prototype.toString.call(/t/) : [object Object]

为什么要用Object.prototype.toString而不是Function.prototype.toString或者其它？这是和他们的toString解释方式有关系的。下面是ECMA中对Object.prototype.toString的解释：

Object.prototype.toString( )

When the toString method is called, the following steps are taken:

1. Get the [[Class]] property of this object.

2. Compute a string value by concatenating the three strings “[object “, Result (1), and “]”.

3. Return Result (2)

其过程简单说来就是：1、获取对象的类名（对象类型）。2、然后将[object、获取的类名、]组合并返回。

ECMA中对Array有如下说明：

The [[Class]] property of the newly constructed object is set to “Array”.

因此我们用如下代码来检测数组：

function isArray(o) {
return Object.prototype.toString.call(o) === '[object Array]';
}

这种方式既解决了instanceof存在的跨页面问题，也解决了属性检测方式所存在的问题，实在是一种妙招，一个很好的解决方案。

除此之外，这种解决办法也可以应用于判断Date,Function等类型的对象