op = Object.prototype,
   ostring = op.toString,
...

function isFunction(it) {
        return ostring.call(it) === '[object Function]';
    }

    function isArray(it) {
        return ostring.call(it) === '[object Array]';
    }

最近在看requireJS的源码时，看到上面一段代码，很是好奇，为啥进行类型判断时使用Object.prototype.toString? 如果是我的话就直接用typeof得了，后来查阅了一些资料：

 

 

typeof

在使用 typeof 运算符时采用引用类型存储值会出现一个问题，无论引用的是什么类型的对象，它都返回 "object"。

 

 

ECMA 对Object.prototype.toString的解释

 

Object.prototype.toString ( )

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

If the this value is undefined, return "[object Undefined]".
If the this value is null, return "[object Null]".
Let O be the result of calling ToObject passing the this value as the argument.
Let class be the value of the [[Class]] internal property of O.
Return the String value that is the result of concatenating the three Strings "[object ", class, and "]".

               var oP = Object.prototype,          toString = oP.toString;                    console.log(toString.call([123]));//[object Array]          console.log(toString.call('123'));//[object String]          console.log(toString.call({a: '123'}));//[object Object]          console.log(toString.call(/123/));//[object RegExp]          console.log(toString.call(123));//[object Number]          console.log(toString.call(undefined));//[object Undefined]          console.log(toString.call(null));//[object Null]          //....
var oP = Object.prototype,
toString = oP.toString;

console.log(toString.call([123]));//[object Array]
console.log(toString.call('123'));//[object String]
console.log(toString.call({a: '123'}));//[object Object]
console.log(toString.call(/123/));//[object RegExp]
console.log(toString.call(123));//[object Number]
console.log(toString.call(undefined));//[object Undefined]
console.log(toString.call(null));//[object Null]
//....