index.js
function on(top) {
  top = typeof top === 'string' ? document.querySelector(top) : top;
  var h = handle.bind(this, top);
  h.once = once.bind(this, top);
  return h;
}
function on(top) {
  top = typeof top === 'string' ? document.querySelector(top) : top;
  var h = handle.bind(this, top);
  h.once = once.bind(this, top);
  return h;
}
Get a handle function for a given top

@param {Element} top The element to begin delegating from
@return {Function}
@api public