Base64 encoding and decoding solutions for modern ES6 JavaScript that encode and decode utf-8 buffers unlike the utf-16 solution on MDN.

utf8-b64.js

function b64enc(input) {
    const encoder = new TextEncoder();
    const unicodeBuffer = encoder.encode(input);

    return btoa(
        String.fromCharCode(
            ...unicodeBuffer
        )
    );
}

function b64dec(input) {
    const rawDecode = atob(input);

    const unicodeBuffer = new Uint8Array(
        [...rawDecode].map(
            (_,i) => rawDecode.charCodeAt(i)
        )
    );

    const decoder = new TextDecoder();
    return decoder.decode(unicodeBuffer);
}