findOverlappingCities.js

function getShowHash (element) {
  return Array.prototype.map.call(element.querySelectorAll('table.data tr'), function (row) {
    var key = row.querySelector('.sortkey');
    var city = row.querySelector('a[href*="City"]');
    if (!key || !city) { return; }
    key = key.textContent;
    city = city.href.match(/\d+$/).pop();
    return { city: city, key: key };
  })
  .filter(function (i) { return i; })
  .reduce(function (hash, curr) {
    hash[curr.city] = hash[curr.city] || [];
    hash[curr.city].push(curr.key);
    return hash;
  }, {});
}

function findHashDiff (hash1, hash2, diff) {
  return Array.from(new Set(Object.keys(hash1).map(function (city) {
    if (!hash2[city]) { return; }
    return hash1[city].map(function (time) {
      return hash2[city].map(function (time2) {
        return Math.abs(time - time2) < diff ? time : undefined;
      })
      .filter(function (e) { return e });
    })
    .filter(function (e) { return e && e.length > 0 })
  })
  .filter(function (e) { return e && e.length > 0 })
  .reduce(function (prev, curr) { return prev.concat(curr); }, [])
  .reduce(function (prev, curr) { return prev.concat(curr); }, [])));
}

function highlightOverlaps (keys) {
  Array.prototype.slice.call(document.querySelectorAll('table.data tr')).forEach(function (row) {
    var key = row.querySelector('.sortkey');
    if (!key) { return }
    key = key.textContent;
    if (keys.indexOf(key) < 0) { return }
    row.querySelector('td').style.fontWeight = 'bold';
  });
}

jQuery
.get(document.location.href.replace(/\/\d+$/, ''))
.then(function (res) {
  var resDom = document.createElement('div');
  resDom.innerHTML = res.replace(/<script(.|\s)*?\/script>/ig, '');
  
  Array.prototype.slice.call(resDom.querySelectorAll('img'))
  .forEach(function (el) {
    el.parentNode.removeChild(el);
  });

  highlightOverlaps(findHashDiff(
    getShowHash(document),
    getShowHash(resDom),
    6));
});