Minimalist jQuery Local Date/Time Script Without Moment.js

localdate.js

$(document).ready(function(){

  // Convert RFC2822 date/time string to local date/time in format MM/DD/YYYY HH:MM XM.
  // Note that PHP has a date format of 'r' that generates RFC2822 format.
  // Wrap your RFC2822 HTML element with the localdate class and this function converts it.
  $('.localdate').each(function(){
    var o = $(this);
    var d = new Date(o.text());
    var s = d.toLocaleString();
    s = s.replace(/(?<!\d)(\d)(?!\d)/g,'0$1');
    var a = s.split(':');
    var n = '' + a[0];
    n += ':' + a[1];
    var a2 = s.split(' ');
    n += ' ' + a2.pop();
    n = n.split(',').join('');
    o.text(n);
  });
  
  // Handy function to display a 3 digit timezone code that also accounts for daylight savings time for the given user's local timezone.
  $('.timezonecode').each(function(){
    var o = $(this);
    o.text((new Date()).toString().match(/\(.*\)/)[0].match(/\b(\w)/g).join('').split('CUT').join('UTC'));
  });

});

This wouldn't take much to convert it from jQuery to Vanilla Javascript. Instead of $(sel), use document.querySelectorAll(sel). Instead of .each(function(){...});, use .forEach(function(el,i){...};. Instead of $(this), use el in the forEach(function(el,i){...}); loop. Instead of .text, use .innerText and as an assignment instead of function. Instead of $(document).ready(function(){...}, use document.addEventListener("DOMContentLoaded", function(event) {...}.