JSFiddle - React, Tailwind, and code Playground

HTML

<div id="text"></div>

JavaScript

var a=null;
var b;
$("#text").append("<div>a is null: " + (a==null) + "</div>");
$("#text").append("<div>a is undefined: " + (a==undefined) + "</div>");
$("#text").append("<div>b is null: " + (b==null) + "</div>");
$("#text").append("<div>b is undefined: " + (b==undefined) + "</div>");
$("#text").append("<div>undefined: " + undefined + "</div>");
$("#text").append("<div>null: " + null+ "</div>");


$("#text").append("<br>")
$("#text").append("<br> a is undefined: " + (typeof(a)=="undefined") );
$("#text").append("<br>b is undefined: " + (typeof(b)=="undefined") + "</div>");
$("#text").append("<br>typeof(a):" + typeof(a));
$("#text").append("<br>typeof(b):" + typeof(b));