Little function that returns the matching node by classname. Useful in all browsers

closestEl.js

function closestEl(elem, elClass) {
  var node = elem
  while (node.parentElement) {
    node = node.parentElement
    if (node.classList.contains(elClass)) {
      break
    }
  }
  node = node.classList.contains(elClass) ? node : elem
  return node
}