JSFiddle - React, Tailwind, and code Playground

JavaScript

function arrayBufferToBase64(buffer)
{
    var binary = ''
    var bytes = new Uint8Array(buffer)
    var len = bytes.byteLength;
    for (var i = 0; i < len; i++)
        binary += String.fromCharCode( bytes[i] );
    return window.btoa(binary);
}

function base64ToArrayBuffer(base64)
{
    var binary_string =  window.atob(base64);
    var len = binary_string.length;
    var bytes = new Uint8Array(len);
    for (var i = 0; i < len; i++)
        bytes[i] = binary_string.charCodeAt(i);
    return bytes.buffer;
}

let gulp = Uint8Array.of(123, 21, 89).buffer;
let encoded = arrayBufferToBase64(gulp);
let decoded = base64ToArrayBuffer(encoded);
console.log(new Uint8Array(decoded));