pancakescon timezone converter

pancakescon.user.js

// ==UserScript==
// @name        pancakescon timezone converter
// @version     1
// @namespace   https://beta.vero.site/
// @include     https://pancakescon.com/attend/
// @grant       none
// @description poorly translate the times to your local time zone on pancakescon.com
// ==/UserScript==

function signed(n) {
  return ((n >= 0) ? '+' : '') + n;
}
function pad2(s) {
	s = String(s);
	return '0'.repeat(Math.max(0, 2 - s.length)) + s;
}

const tds = document.querySelectorAll('figure.is-style-stripes table td:first-child');
const utcOffset = -new Date().getTimezoneOffset(); // UTC to local
// why is this negative?? one can only speculate...
// https://stackoverflow.com/questions/21102435/why-does-javascript-date-gettimezoneoffset-consider-0500-as-a-positive-off
const offset = utcOffset + 300; // UTC-5 to local
for (let td of tds) {
  td.textContent = td.textContent.replaceAll(/\b\d{4}\b/g, (s) => {
    let allMins = 60 * Number(s.substr(0, 2)) + Number(s.substr(2, 4)) + offset;
    let days = Math.floor(allMins / 1440);
    let dayMins = allMins - (days * 1440);
    let res = pad2(Math.floor(dayMins / 60)) + ':' + pad2(dayMins % 60);
    if (days !== 0) res = '(' + signed(days) + ')' + res;
    return res;
  });
}

document.querySelector('figure.is-style-stripes table th:first-child').textContent = 'UTC' + signed(utcOffset/60);

for (let disclaimer of document.querySelectorAll('strong')) {
  console.log(disclaimer.textContent);
  if (disclaimer.textContent.startsWith('All times')) {
    disclaimer.style.textDecoration = 'line-through';
    disclaimer.parentNode.appendChild(document.createTextNode(' Questionably converted to UTC' + signed(utcOffset/60)));
    break;
  }
}