Missing function from tutorial about web-push-codelab HOT 6 OPEN

/**
 * urlBase64ToUint8Array
 * 
 * @param {string} base64String a public vavid key
 */
function urlBase64ToUint8Array(base64String) {
    var padding = '='.repeat((4 - base64String.length % 4) % 4);
    var base64 = (base64String + padding)
        .replace(/\-/g, '+')
        .replace(/_/g, '/');

    var rawData = window.atob(base64);
    var outputArray = new Uint8Array(rawData.length);

    for (var i = 0; i < rawData.length; ++i) {
        outputArray[i] = rawData.charCodeAt(i);
    }
    return outputArray;
}