Decimate issues button for GitHub

thanos.js

const buttonHtml = `
<a id="thanos" class="btn btn-primary float-right" role="button"
  style="margin-left:38px">
  Decimate issues
</a>`;


var css = '#thanos:hover{ background-image: linear-gradient(-180deg,#6d3678,#693270 90%) }';
var style = document.createElement('style');

if (style.styleSheet) {
    style.styleSheet.cssText = css;
} else {
    style.appendChild(document.createTextNode(css));
}

document.getElementsByTagName('head')[0].appendChild(style);

document
  .querySelector(".subnav .pr-2")
  .insertAdjacentHTML("beforeend", buttonHtml);

const $button = document.getElementById("thanos");
const $tabCount = document.querySelector(
  "#js-repo-pjax-container > div.pagehead.repohead.instapaper_ignore.readability-menu.experiment-repo-nav > nav > span:nth-child(2) > a > span.Counter"
);
const $openCount = document.querySelector(
  "#js-issues-toolbar > div > div > div.flex-auto > div > a.btn-link.selected"
);
const $closedCount = document.querySelector(
  "#js-issues-toolbar > div > div > div.flex-auto > div > a:nth-child(2)"
);

document.body.style.transition =
  "filter 0.4s cubic-bezier(0.55, 0.055, 0.675, 0.19)";

const state = {
  openCount: parseFloat($openCount.childNodes[2].nodeValue.replace(/,/g, '')),
  closedCount: parseFloat($closedCount.childNodes[2].nodeValue.replace(/,/g, '')),
  brightness: 100,
  start: null
};

const duration = 12000;

$button.onclick = () => {
  state.brightness = 1000;
  state.start = performance.now();
  render();
  state.brightness = 100;
  setTimeout(() => requestAnimationFrame(loop), 500);
};

function loop() {
  render();
  requestAnimationFrame(loop);
}

function render() {
  const t =
    state.start &&
    Math.min(duration, performance.now() - state.start) / duration;
  const killed = Math.round((easeInOut(t) * state.openCount) / 2);
  const open = state.openCount - killed;
  const close = state.closedCount + killed;

  $tabCount.innerText = open.toLocaleString();
  $openCount.childNodes[2].nodeValue = ` ${open.toLocaleString()} Open`;
  $closedCount.childNodes[2].nodeValue = ` ${close.toLocaleString()} Closed`;
  
  document.body.style.filter = `brightness(${state.brightness}%)`;
}

render();

function easeInOut(t) {
  return t < 0.5 ? 8 * t * t * t * t : 1 - 8 * --t * t * t * t;
}