JSFiddle - React, Tailwind, and code Playground

HTML

<div id="before"></div>
<div id="after"></div>

JavaScript

var a=[0,1,2];
$("#before").text("before adding 5th integer: a[0]="+a[0]+",a[1]="+a[1]+",a[2]="+a[2])

 a[4]=4;
$("#after").text("after adding 5th integer: a[0]="+a[0]+",a[1]="+a[1]+",a[2]="+a[2]+",a[3]="+a[3]+",a[4]="+a[4])