broadcastAppEvent function
Implementation
void broadcastAppEvent(int viewId, String name, JSObject data) {
final HTMLElement? root = ui_web.views.getHostElement(viewId) as HTMLElement?;
assert(root != null, 'Flutter root element cannot be found!');
final eventDetails = CustomEventInit(detail: data);
eventDetails.bubbles = true;
eventDetails.composed = true;
root!.dispatchEvent(CustomEvent(name, eventDetails));
}