function addHandler()

in applications/clouddemo/net4/CloudDemo.Mvc/Scripts/bootstrap.esm.js [416:453]

• 31 lines of code
• 13 McCabe index (conditional complexity)

function addHandler(element, originalTypeEvent, handler, delegationFunction, oneOff) {
  if (typeof originalTypeEvent !== 'string' || !element) {
    return;
  }

  let [isDelegated, callable, typeEvent] = normalizeParameters(originalTypeEvent, handler, delegationFunction); // in case of mouseenter or mouseleave wrap the handler within a function that checks for its DOM position
  // this prevents the handler from being dispatched the same way as mouseover or mouseout does

  if (originalTypeEvent in customEvents) {
    const wrapFunction = fn => {
      return function (event) {
        if (!event.relatedTarget || event.relatedTarget !== event.delegateTarget && !event.delegateTarget.contains(event.relatedTarget)) {
          return fn.call(this, event);
        }
      };
    };

    callable = wrapFunction(callable);
  }

  const events = getElementEvents(element);
  const handlers = events[typeEvent] || (events[typeEvent] = {});
  const previousFunction = findHandler(handlers, callable, isDelegated ? handler : null);

  if (previousFunction) {
    previousFunction.oneOff = previousFunction.oneOff && oneOff;
    return;
  }

  const uid = makeEventUid(callable, originalTypeEvent.replace(namespaceRegex, ''));
  const fn = isDelegated ? bootstrapDelegationHandler(element, handler, callable) : bootstrapHandler(element, callable);
  fn.delegationSelector = isDelegated ? handler : null;
  fn.callable = callable;
  fn.oneOff = oneOff;
  fn.uidEvent = uid;
  handlers[uid] = fn;
  element.addEventListener(typeEvent, fn, isDelegated);
}