判断js数据类型的函数实例详解

function judgeType(change) {
    if (arguments.length == 0) {
      return '0';//无参数传入
    }
    if (change === null) {
      return 'null'
    }
    if (change === undefined && arguments.length > 0) {
      return 'undefined'
    }
    if (change instanceof Function) {
      return 'function'
    }
    if (change instanceof Array) {
      return 'arry'
    }
    if (change instanceof Number || typeof change == 'number') {
      return 'number'
    }
    if (change instanceof String || typeof change == 'string') {
      return 'string'
    }
    if (change instanceof Boolean || typeof change == 'boolean') {
      return 'boolean'
    }
  }

 typeof  2   输出  number
    typeof  null  输出  object
    typeof  {}  输出  object
    typeof  []  输出  object
    typeof  (function(){})  输出 function 
    typeof  undefined     输出 undefined
    typeof  '222'         输出  string 
   typeof true          输出   boolean 

  var  gettype=Object.prototype.toString
    gettype.call('aaaa')    输出   [object String]
    gettype.call(2222)     输出   [object Number]
    gettype.call(true)     输出   [object Boolean]
    gettype.call(undefined) 输出   [object Undefined]
    gettype.call(null)         输出  [object Null]
     gettype.call({})          输出  [object Object]
     gettype.call([])          输出  [object Array]
     gettype.call(function(){})   输出  [object Function]

''.constructor==String   
      [].constructor==Array
      var obj= new Object()  
  obj.constructor==Object

 var  gettype=Object.prototype.toString
   var  utility={
     isObj:function(o){
        return  gettype.call(o)=="[object Object]";
     },
     isArray:function(o){
        return  gettype.call(o)=="[object Array]";
     },
     isNULL:function(o){
        return  gettype.call(o)=="[object Null]";
     },
     isDocument:function(){
         return  gettype.call(o)=="[object Document]"|| [object HTMLDocument];
     }
     ........
  }

var Type = (function() {
        var type = {};
        var typeArr = ['String', 'Object', 'Number', 'Array','Undefined', 'Function', 'Null', 'Symbol'];
        for (var i = 0; i < typeArr.length; i++) {
          (function(name) {
            type['Is' + name] = function(obj) {
              return Object.prototype.toString.call(obj) == '[object ' + name + ']';
            }
          })(typeArr[i]);
        }
        return type;
})();