Use typeof to determine data type
(1) Judging basic data types

//Number type
typeof 1;//"number"
//Boolean type
typeof true;// "boolean"
//String type
typeof "zzz";// "string"
//Undefined
typeof  undefined;// "undefined"
//object
function Person(name, age) {
    this.name = name;
    this.age = age;
}
var person = new Person("Rose", 18);
typeof person;//"object"

Using typeof to determine data types in JavaScript, you can only distinguish between five basic types: number, string, undefined, boolean, and object.
Arrays, functions, and objects are intricately related, and typeof returns a uniform "object" string.

Use Object.prototype Native toString() method on to determine data type
(1) Judging basic types

Object.prototype.toString.call(null);//"[object Null]"
Object.prototype.toString.call(undefined);//"[object Undefined]"
Object.prototype.toString.call("abc");//"[object String]"
Object.prototype.toString.call(123);//"[object Number]"
Object.prototype.toString.call(true);//"[object Boolean]"

(2) Determining the Type of Native Reference

//Function type
Function fn(){console.log("test");}
Object.prototype.toString.call(fn);//"[object Function]"
//Date type
var date = new Date();
Object.prototype.toString.call(date);//"[object Date]"
//Array type
var arr = [1,2,3];
Object.prototype.toString.call(arr);//"[object Array]"
//regular expression
var reg = /[hbc]at/gi;
Object.prototype.toString.call(arr);//"[object Array]"
//Custom Type
function Person(name, age) {
    this.name = name;
    this.age = age;
}
var person = new Person("Rose", 18);
Object.prototype.toString.call(person ); //"[object Object]"
//It is obvious that this method does not accurately determine that person is an instance of the Person class, it can only be usedinstanceof Operators to make judgments, as follows:
console.log(person instanceof Person);//Output result is true

(3) Judging native JSON objects

var isNativeJSON = window.JSON && Object.prototype.toString.call(JSON);
console.log(isNativeJSON);//The output is "[object JSON]" which indicates that the JSON is native, otherwise it is not;

Be careful:Object.prototype.toString() itself is allowed to be modified, and what we are discussing now isObject.prototype.toStringThe application of this method assumes that the toString() method has not been modified as a precondition.