JS string rotation Byte64 []

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;
}