web push 当用户已打开网页时不进行通知

self.addEventListener('push', function(event) {
    clients.matchAll().then( windowClients => {
    console.log(windowClients.length);
    if (windowClients.length<1){ //说明没有打开网站
        const msg = event.data.json()
        const title = 'title';
        const options = {
            body:msg.body,
            tag:msg.tag,
            icon:'icon.png',
        };
        event.waitUntil(self.registration.showNotification(title, options));
    }
    })
  });