JavaScript判断数据类型的方法

1. 利用运算符typeof或者typeof()方法
   

   　　     //基本类型

           console.log(typeof 1);              //1

           console.log(typeof true);           //boolean

           console.log(typeof undefined);      //undefined

           console.log(typeof 'string');       //string

           console.log(typeof null);           //object

           console.log(typeof Symbol());       //symbol

           console.log(typeof 33n);            //bigint

           //对象类型

           console.log(typeof []);             //object

           console.log(typeof function(){});   //function

           console.log(typeof {});             //object

           console.log(typeof new Set([1,2,3]));//object

           console.log(typeof new Map([['o',1]]));//object

           console.log(typeof p1);                 //object    

   由此可以看出typeof运算符值对原始数据类型有用，对于对象数据类型就并没有那么准确

2. instanceof运算符
   

   console.log(1 instanceof Number);       //false
   console.log('str' instanceof String);   //false
   console.log([] instanceof Array);       //true
   console.log([] instanceof Object);      //true   
    

   首先，我们知道instanceof运算符是判断构造函数的prototype是否出现在实例的原型链上面，因此，此方法并不太适用判断数据类型

3. constructor属性
   

   //原始数据类型
           console.log((1).constructor);        //ƒ Number() { [native code] }
           console.log('str'.constructor);      //ƒ String() { [native code] }
           console.log(true.constructor);      //ƒ Boolean() { [native code] }
           console.log(null.constructor);      // 报错
           console.log(undefined.constructor);  //报错
           console.log((88n).constructor);        //ƒ BigInt() { [native code] }
           console.log(Symbol().constructor);      //ƒ Symbol() { [native code] }
    //对象数据类型
           console.log([].constructor);        //ƒ Array() { [native code] }
           console.log(function(){}.constructor);        //ƒ Function() { [native code] }
           console.log({}.constructor);        //ƒ Object() { [native code] }
           console.log(new Set([1,2,3]).constructor);        //ƒ Set() { [native code] }
           console.log(new new Map([['o',1]]).constructor);        //Map(0) {}

   虽然看似很完美BUT。。。。

   console.log(Number.prototype.constructor);  //ƒ Number() { [native code] }
   console.log(String.prototype.constructor);  //ƒ String() { [native code] }

   由于constructor属性是定义在对象的原型上面，所以原型对象的constructor属性也直接指向构造函数

4. 借用Object原型里的一个方法 ：Object.prototype.toString.call(对象)

       console.log(Object.prototype.toString.call(null));//[object Null]
       console.log(Object.prototype.toString.call(undefined)); //[object Undefined]
       console.log(Object.prototype.toString.call(true)); //[object Boolean]
       console.log(Object.prototype.toString.call('str'));//[object String]
       console.log(Object.prototype.toString.call(11));//[object Number]
       console.log(Object.prototype.toString.call(function(){}));//[object Function]
       console.log(Object.prototype.toString.call([]));//[object Array]
       console.log(Object.prototype.toString.call({}));//[object Object]
       console.log(Object.prototype.toString.call(new Set([4,5,6])));  //[object Set]

   此方法相对来说还是比较完美，但是要注意一定是从Object.prototype.toString用call方法借用才行