Base64 Encode/Decode in JavaScript

// Browser: btoa/atob
const encoded = btoa('Hello World');  // 'SGVsbG8gV29ybGQ='
const decoded = atob('SGVsbG8gV29ybGQ=');  // 'Hello World'

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

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

// Node.js: Buffer
const encoded = Buffer.from('Hello World').toString('base64');
const decoded = Buffer.from('SGVsbG8gV29ybGQ=', 'base64').toString('utf8');

// Base64 URL safe (replace +/ with -_)
const urlSafe = encoded.replace(/\+/g, '-').replace(/\//g, '_').replace(/=/g, '');

// Decode URL safe
const standard = urlSafe.replace(/-/g, '+').replace(/_/g, '/');
const padded = standard + '='.repeat((4 - standard.length % 4) % 4);