prevselect.js

function selectIfPreviousAll(base, previous) {
  var matches = [];

  document.querySelectorAll(base).forEach(function(e) {
    var siblings = e.parentElement.childNodes;
    if(siblings.length < 2)
      return;

    var eIndex = Array.prototype.indexOf.call(siblings, e);
    matches.push(siblings[eIndex - 1]);
  });

  return matches;
}