JSFiddle - React, Tailwind, and code Playground

HTML

<div id="whole_array"></div><br>
<div id="first_item"></div><br>
<div id="second_item"></div><br>
<div id="item_total"></div><br>
<div id="counter_total"></div><br>

JavaScript

a = [];

a[a.length] = "item a ";
a[a.length] = "item b ";
a[a.length] = "item c ";
a[a.length] = "item d ";

bar = a.length;

a[ bar++ ] = "new item a ";
a[ bar++ ] = "new item b ";

document.getElementById('whole_array').innerHTML = a;
document.getElementById('first_item').innerHTML = a[0];
document.getElementById('second_item').innerHTML = a[1];
document.getElementById('item_total').innerHTML = a.length;
document.getElementById('counter_total').innerHTML = bar;