js中有六種資料型別，包括五種基本資料型別（Number,String,Boolean,Undefined,Null）,和一種複雜資料型別（Object）。

typeof

由於js中的變數是鬆散型別的，所以它提供了一種檢測當前變數的資料型別的方法，也就是typeof關鍵字.

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

可以看到 typeof 在對複雜型別進行判斷統一都是object型別的

 toString方法可以獲得複雜物件型別更加詳細的資訊

var toString = {}.toString
console.log(toString.call(new Date))     //[object Date]
console.log(toString.call([]))                //[object Array]
console.log(toString.call({}))               //[object Object]

封裝函式

var toString = {}.toString
    var types = {"[object Boolean]":"boolean","[object Number]":"number","[object String]":"string","[object Function]":"function","[object Array]":"array","[object Date]":"date","[object RegExp]":"regexp","[object Object]":"object","[object Error]":"error"}
    
 
function getType( obj ) {
        //如果為null 或者 undefined 直接返回 'null'，'undefined'
        if ( obj == null ) {
            console.log(1,obj)
            return String( obj );
        }
        //如果是複雜物件型別或者函式型別
        if(typeof obj === "object" || typeof obj === "function"){
            return types[ toString.call(obj) ] || "object"
            //如果是基本型別
        }else {
            return typeof obj
        }
    }

    console.log(getType(123))       //number
    console.log(getType('abc'))     //string
    console.log(getType(true))      //boolean
    console.log(getType(new String()))  //string
    console.log(getType(new Number()))  //number
    console.log(getType(undefined))     //undefined
    console.log(getType(null))          //null
    console.log(getType({}))            //object
    console.log(getType([]))            //array
    console.log(getType(console.log))   //function