Wordpress archive widget to annually grouped list

wordpress.js

jQuery(function() {
  var archive = jQuery('.widget_archive li a').toArray().map(function(item) {
    var t = item.innerText.split(/ /);
    return {
      'link': item.getAttribute('href'),
      'year': parseInt(t[1], 10),
      'month': t[0],
      'count': parseInt(item.parentNode.innerText.match(/\(([0-9]+)\)$/)[1], 10)
    };
  }).reduce(function(memo, item) {
    if (!memo.hasOwnProperty(item.year)) { memo[item.year] = { items: [], count: 0 }; }
    memo[item.year].count += item.count;
    memo[item.year].items.push({ name: item.month, count: item.count, link: item.link });
    return memo;
  }, {});
  
  var years = Object.keys(archive).reverse();
  var root = document.createElement('ul');
  for(var i = 0; i < years.length; i++) {
    var yLi = document.createElement('li');
    var yLink = document.createElement('a');
    yLink.innerText = years[i] + " (" + archive[years[i]].count + ")";
  
    var mUl = document.createElement('ul');
    var mItems = archive[years[i]].items;
    for (var j = 0; j < mItems.length; j++) {
      var m = mItems[j];
      var mLi = document.createElement('li');
      var link = document.createElement('a');
      link.setAttribute('href', m.link);
      link.innerText = m.name + " (" + m.count + ")";
      mLi.appendChild(link);
      mUl.appendChild(mLi);
    }
  
    yLink.addEventListener('click', function() {
      jQuery(this).next('ul').toggle()
    });
  
    jQuery(mUl).hide();
  
    yLi.appendChild(yLink);
    yLi.appendChild(mUl);
  
    root.appendChild(yLi);
  }
  jQuery('.widget_archive ul').remove();
  jQuery('.widget_archive').append(root);
  jQuery('.widget_archive ul li:first ul').show();
});