js base64 with btoa and atob,

base64.js

function strToB64(str) {
    return btoa(encodeURIComponent(str).replace(/%([0-9A-F]{2})/g, function(match, p1) {
        return String.fromCharCode('0x' + p1);
    }));
}

function b64ToStr(b64Str) {
    return decodeURIComponent(atob(b64Str).split('').map(function(c) {
        return '%' + ('00' + c.charCodeAt(0).toString(16)).slice(-2);
    }).join(''));
}

function buffToB64(buffer) {
    return btoa([].slice.call(new Uint8Array(buffer)).map(function (bin) {
        return String.fromCharCode(bin);
    }).join(""));
}

function b64ToBuff(b64Str) {
    return Uint8Array.from(atob(b64Str), c => c.charCodeAt(0)).buffer;
}