判定类型

目前最精确的判定方法（不包括自定义类型）

//2010.6.1更新

        var is = function (obj,type) {

        return (type === "Null" && obj === null) ||

        (type === "Undefined" && obj === void 0 ) ||

        (type === "Number" && isFinite(obj)) ||

         Object.prototype.toString.call(obj).slice(8,-1) === type;

    },

用法如下：

//***************示例一，判定数组与函数

        var forEach = function(array,fn,bind){

          if(is(array,"Array") && is(Array.forEach,"Function")){

            array.forEach(fn,bind);

          }else{

            for(var i=0,n=array.length;i<n;i++){

              i in array && fn.call(bind,array[i],i,array)

            }

          }

        }

//***************示例二，判定null

var a = null

alert(is(a,"Null"))

//***************示例二，判定undefined

var b

alert(is(b,"Undefined"))

另一个变种，直接返回表示类型的字符串

var getType = function (obj) {

  var _toString = Object.prototype.toString,undefined;

  return obj === null? "Null":

    obj === undefined ? "Undefined":

    _toString.call(obj).slice(8,-1);

};

用法：

var arr = [1,2,3,4]

      alert(getType(arr));//Array

      var nil = null

      alert(getType(nil))//Null

      var und ;

      alert(getType(und))//Undefined

      var spans = document.getElementsByTagName("span");

      alert(getType(spans)) //HTMLCollection

      alert(getType(spans[0].childNodes))//NodeList

var _toS = {}.toString,

    _types = {

    'undefined' : 'undefined',

    'number' : 'number',

    'boolean' : 'boolean',

    'string' : 'string',

    '[object Function]' : 'function',

    '[object RegExp]' : 'regexp',

    '[object Array]' : 'array',

    '[object Date]' : 'date',

    '[object Error]' : 'error'

};

function type(o) {

    return _types[typeof o] || _types[_toS.call(o)] || (o ? 'object' : 'null');

} 

//2010.7.20

function isA (thing, canon) {

  // special case for null and undefined

  if (thing == null || canon == null) {

    return thing === canon;

  }

  return Object.getPrototypeOf(Object(thing)) == Object.getPrototypeOf(Object(canon));

}

function isBool (thing) {

  return isA(thing, true);

}

function isNumber (thing) {

  return isA(thing, 0) && isFinite(thing);

}

function isString (thing) {

  return isA(thing, "");

}

//2010.11.2更新

//用于取得数据的类型（一个参数时）或判定数据的类型(两个参数时)

// $$$$(type(1,"Number"));

// $$$$(type(NaN,"NaN"));

// $$$$(type(void(0),"Undefined"));

// $$$$(type("aaa","String"));

// $$$$(type([1,2,3],"Array"));

// $$$$(type(/i/,"RegExp"));

// $$$$(type({},"Object"));

// $$$$(type(document,"Document"));

// $$$$(type(document.body,"BODY"));

// $$$$(type(window,"Window"));

// $$$$(type(true,"Boolean"));

// $$$$(type(document.getElementsByTagName('p'),"HTMLCollection"));

 var type = (function(){

        var reg = /^(\w)/,

        regFn = function($,$1){

            return $1.toUpperCase()

        },

        to_s = Object.prototype.toString;

        return function(obj,str){

            var result = (typeof obj).replace(reg,regFn);

            if(result === 'Object' || (result === 'Function' && obj.exec) ){//safari chrome中 type /i/ 为function

                if(obj===null) result = 'Null';

                else if(obj.window==obj) result = 'Window'; //返回Window的构造器名字

                else if(obj.callee) result = 'Arguments';

                else if(obj.nodeType === 9) result = 'Document';

                else if(obj.nodeName) result = (obj.nodeName+'').replace('#',''); //处理元素节点

                else if(!obj.constructor || !(obj instanceof Object)){

                    if("send" in obj && "setRequestHeader" in obj){//处理IE5-8的宿主对象与节点集合

                        result = "XMLHttpRequest"

                    }else if("length" in obj && "item" in obj){

                        result = "namedItem" in obj ?  'HTMLCollection' :'NodeList';

                    }else{

                        result = 'Unknown';

                    }

                }else result = to_s.call(obj).slice(8,-1);

            }

            if(result === "Number" && isNaN(obj))  result = "NaN";

            //safari chrome中 对 HTMLCollection与NodeList的to_s都为 "NodeList",此bug暂时无解

            if(str){

                return str === result;

            }

            return result;

        }

    })()

再来个精简版

//2011.7.29

    function isType (obj, type) {

        return toString.call(obj).indexOf('[object ' + type) == 0;

    }

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