[Gist Age Highlighter] Highlights the age of different Github Gist results, based on age #UserScript

GistAgeHighlighter.user.js

// ==UserScript==
// @name         Gist Age Highlighter
// @description  Highlights the age of different Github Gist results, based on age
// @version      0.4
// @author       rjf89
// @match        https://gist.github.com/search*
// @grant        none
// ==/UserScript==
Array.prototype.flatMap = function(lambda) { return Array.prototype.concat.apply([], this.map(lambda)); };
const setColor          = (e, bgColor) => e.parentElement.style = `background-color: ${bgColor}; color: ivory`;

function highlightElement(e) {
  if (e.innerText) {
    if (/years? ago/.test(e.innerText))  setColor(e, 'darksalmon');
    if (/months? ago/.test(e.innerText)) setColor(e, 'darkorange');
    if (/weeks? ago/.test(e.innerText))  setColor(e, 'aliceblue');
    if (/days? ago/.test(e.innerText))   setColor(e, 'greenyellow');
  }
}

[...document.querySelectorAll('time-ago')].forEach(highlightElement);

const gistResults = document.querySelector('div.repository-content.gist-content > div > div.column.three-fourths');
const mutationConditions = { childList: true, subtree: true };
new MutationObserver((mutationsList) => [...mutationsList]
                     .filter(mutation => !!mutation.addedNodes)
                     .flatMap(mutation => [...mutation.addedNodes])
                     .filter(node => node.querySelectorAll)
                     .flatMap(node => [...node.querySelectorAll('time-ago')])
                     .forEach(highlightElement)
).observe(gistResults, mutationConditions);