Function handler

tools/cli/src/webpack/error-handler.js:39–64

* @param event {PromiseRejectionEvent|ErrorEvent}

(event)

   * @param event {PromiseRejectionEvent|ErrorEvent}
   */
  function handler(event) {
    var error;

    if ('error' in event) {
      error =
        event.error ||
        (event.message === 'Script error.'
          ? new SyntaxError(event.message)
          : new Error(event.message));
    } else {
      error = event.reason;
    }

    console.error('unhandled unrecoverable error', error);

    var shouldCache =
      // syntax error
      error && error instanceof SyntaxError;

    if (!shouldCache) {
      return;
    }

    event.stopImmediatePropagation();
    showGlobalErrorPage();
  }

  function registerGlobalErrorHandler() {
    if (typeof document !== 'undefined') {