4 methods for js data type detection

1.typeof

Disadvantages: It is not very convenient to detect types such as null and Array

Js code

typeof null; //"object"

typeof []; //"object"

2.instanceof

Disadvantages: 1. Only applicable to object types

2. As long as the current class is on the prototype chain of the instance, the detected results are true

Js code

123 instanceof Number; //false

null instanceof null; //TypeError

null instanceof Object; //false

function A(){}

function B(){}

A.prototype=new B();

var aObj=new A() ;

aObj instanceof B;//true

aObj instanceof A;//true

3.constructor

Note: An error will occur during class inheritance

Js code

function A(){};

function B(){};

A.prototype = new B();

var aObj = new A();

aObj.constructor === B; //true;

aObj.constructor === A; //false;

4. Custom method implementation (more general)

Js code

function getType(o){

return Object.prototype.toString.call(o).slice(8,-1 ;

getType({}); //"Object"

getType(()=>{}); //"Function"

getType(document.createElement('div')); //"HTMLDivElement"