typeof 返回值有六種可能： "number," "string," "boolean," "object," "function," 和 "undefined."

                var a;
                var a1='people'.name;
                alert("a的型別" + typeof a);//undefined
                alert("a1的型別" + typeof a1);//undefined

                var b = false;
                alert("b的型別" + typeof b);//boolean

                var c = 'abc';
                alert("c的型別" + typeof c);//string

                var d = 2;
                var d1 = 2.3;
                alert("d的型別" + typeof d);//number
                alert("d1的型別" + typeof d1);//number

                var e = function () {
                };
                var e1 = function () {
                    return 1;
                };
                alert("e的型別" + typeof e);//function
                alert("e1的型別" + typeof e1);//function

                var f = null;
                var f1= [];f1[f1.length]="張三";
                alert("f的型別" + typeof f);//object
                alert("f1的型別" + typeof f1);//object
 

想區別物件、陣列 單純使用 typeof 是不行的，JavaScript中,通過Object.prototype.toString方法，判斷某個物件值屬於哪種內建型別。

由於 JavaScript 中一切都是物件，任何都不例外，對所有值型別應用 Object.prototype.toString.call() 方法結果如下：

<script  type="text/javascript">

console.log(typeof 123)//number
console.log(typeof '123')//string
console.log(typeof true)//boolean
console.log(typeof function(){})//function
console.log(typeof {})//object
console.log(typeof [])//object
console.log(typeof new Date())//object
console.log(typeof null)//object
console.log(typeof  undefined)//undefined


console.log(Object.prototype.toString.call(123)) //[object Number]
console.log(Object.prototype.toString.call('123')) //[object String]
console.log(Object.prototype.toString.call(true)) //[object Boolean]
console.log(Object.prototype.toString.call(function(){})) //[object Function]
console.log(Object.prototype.toString.call({})) //[object Object]
console.log(Object.prototype.toString.call([])) //[object Array]
console.log(Object.prototype.toString.call(new Date()) )//[object Date]
console.log(Object.prototype.toString.call(null)) //[object Null]
console.log(Object.prototype.toString.call(undefined)) //[object Undefined]



</script>
 

判斷是否為函式

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

判斷是否為陣列：

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