util.js

function urlB64ToUint8Array(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;
}

function subscribePush(registration) {
    return getPublicKey().then(function (key) {
        return registration.pushManager.subscribe({
            userVisibleOnly: true,
            applicationServerKey: key
        });
    });
}

function getPublicKey() {
    return fetch('./api/push/vapidpublickey')
        .then(function (response) {
            return response.json();
        })
        .then(function (data) {
            return urlB64ToUint8Array(data);
        });
}

function saveSubscription(subscription) {
    return fetch('./api/push/subscribe', {
        method: 'post',
        headers: {
            'Content-type': 'application/json'
        },
        body: JSON.stringify({
            subscription: subscription
        })
    })
        .then(response => response.json())
        .then(response => {
            localStorage.setItem('userId', response.userId);
        });
}

function deleteSubscription(subscription) {
    return fetch('./api/push/unsubscribe', {
        method: 'post',
        headers: {
            'Content-type': 'application/json'
        },
        body: JSON.stringify({
            subscription: subscription
        })
    });
}