Base64 in browser with Unicode support (no deprecated 'unescape' and 'escape' functions)

b64utf.js

const b64EncodeUnicode = (str) => (
  window.btoa(window.encodeURIComponent(str).replace(/%([0-9A-F]{2})/g, (_match, p1) => (
    String.fromCharCode(`0x${p1}`)
  )))
)

const b64DecodeUnicode = (str) => (
  window.decodeURIComponent(window.atob(str).split('').map((c) => (
    `%${`00${c.charCodeAt(0).toString(16)}`.slice(-2)}`
  )).join(''))
)