JSFiddle - React, Tailwind, and code Playground

HTML

<p id="am"></p>
<p id="pm"></p>

JavaScript

var timeString = "11:59";
var H = +timeString.substr(0, 2);
var h = (H % 12) || 12;
if (h <= 9) {
    h = '0' + h;
}
var ampm = H < 12 ? " AM" : " PM";
timeString = h + timeString.substr(2, 3) + ampm;
document.getElementById('am').innerHTML = timeString;


var timeString = "23:59";
var H = +timeString.substr(0, 2);
var h = (H % 12) || 12;
if (h <= 9) {
    h = '0' + h;
}
var ampm = H < 12 ? " AM" : " PM";
timeString = h + timeString.substr(2, 3) + ampm;
document.getElementById('pm').innerHTML = timeString;