material-web/controller/events.ts

/**
 * @license
 * Copyright 2021 Google LLC
 * SPDX-License-Identifier: Apache-2.0
 */

/**
 * Re-dispatches an event from the provided element.
 *
 * This function is useful for forwarding non-composed events, such as `change`
 * events.
 *
 * @example
 * class MyInput extends LitElement {
 *   render() {
 *     return html`<input @change=${this.redispatchEvent}>`;
 *   }
 *
 *   protected redispatchEvent(event: Event) {
 *     redispatchEvent(this, event);
 *   }
 * }
 *
 * @param element The element to dispatch the event from.
 * @param event The event to re-dispatch.
 * @return Whether or not the event was dispatched (if cancelable).
 */
export function redispatchEvent(element: Element, event: Event) {
  // For bubbling events in SSR light DOM (or composed), stop their propagation
  // and dispatch the copy.
  if (event.bubbles && (!element.shadowRoot || event.composed)) {
    event.stopPropagation();
  }

  const copy = Reflect.construct(event.constructor, [event.type, event]);
  const dispatched = element.dispatchEvent(copy);
  if (!dispatched) {
    event.preventDefault();
  }

  return dispatched;
}