tachyonjs/tachyon.js

// tachyon.js 2.0.1 - @weebney - MIT License
const bodyDataValues = document.body.dataset;
const whitelistEnabled = 'tachyonWhitelist' in bodyDataValues;
const sameOriginOnly = 'tachyonSameOrigin' in bodyDataValues;
const timerDuration = bodyDataValues.tachyonTimer || 50;
let lastTouchedAnchor = null;

function toggleLinkTag() {
  lastTouchedAnchor = lastTouchedAnchor ? null : this;
  const linkTagId = 'tachyon';
  const linkTag = document.getElementById(linkTagId);
  if (linkTag) {
    linkTag.remove();
  } else {
    setTimeout(() => {
      if (lastTouchedAnchor === this) {
        const newLinkElement = document.createElement('link');
        newLinkElement.id = linkTagId;
        newLinkElement.href = this.href;
        newLinkElement.rel = 'prerender';
        document.head.appendChild(newLinkElement);
      }
    }, timerDuration);
  }
}

function initializeListeners(node) {
  if (node.dataset) {
    const listed = 'tachyon' in node.dataset;
    if ((node.tagName === 'A' && node.href) && (listed === whitelistEnabled || sameOriginOnly)
    && (!sameOriginOnly || (listed || (node.origin === window.location.origin)))) {
      ['mouseover', 'mouseout', 'touchstart', 'touchend'].forEach((eventName) => node.addEventListener(eventName, toggleLinkTag, { passive: true }));
    }
  }
}

const mutationObserver = new MutationObserver((mutationRecordArray) => mutationRecordArray
  .forEach((record) => record.addedNodes.forEach(initializeListeners)));

mutationObserver.observe(document.body, { childList: true, subtree: true });

document.querySelectorAll('a').forEach(initializeListeners);