サービスワーカー、フロント側のコード．スターウォーズみたいだね．

if ('serviceWorker' in navigator && 'PushManager' in window) {
    navigator.serviceWorker.ready.then(function(registration) {
        registration.pushManager.subscribe({
            userVisibleOnly: true,
            applicationServerKey: urlBase64ToUint8Array('VAPID_PUBLIC_KEY')
        }).then(function(subscription) {
            fetch('/api/save-subscription', {
                method: 'POST',
                headers: {
                    'Content-Type': 'application/json',
                },
                body: JSON.stringify(subscription),
            });
        }).catch(function(error) {
            console.error('Push subscription error:', error);
        });
    });
}

function urlBase64ToUint8Array(base64String) {
    const padding = '='.repeat((4 - base64String.length % 4) % 4);
    const base64 = (base64String + padding).replace(/-/g, '+').replace(/_/g, '/');
    const rawData = window.atob(base64);
    const outputArray = new Uint8Array(rawData.length);
    for (let i = 0; i < rawData.length; ++i) {
        outputArray[i] = rawData.charCodeAt(i);
    }
    return outputArray;
}