code: function addEventListeners(el, eventName, handlers) {
    var handler;
    var i;
  
    if (!handlers) {
      return;
    }
  
    // Convert to array.
    if (handlers.constructor === Function) {
      handlers = [handlers];
    }
  
    // Register.
    for (i = 0; i < handlers.length; i++) {
      el.addEventListener(eventName, handlers[i]);
    }
  }
docs: Register event handlers for an event name to ref.
  
  @param {Element} el - DOM element.
  @param {string} eventName
  @param {array|function} eventHandlers - Handler function or array of handler functions.