btoa.js/README.md

btoa

A port of the browser's btoa function.

Uses Buffer to emulate the exact functionality of the browser's btoa (except that it supports unicode and the browser may not).

It turns binary data to base64-encoded ascii.

(function () {
  "use strict";
  
  var btoa = require('btoa')
    , bin = "Hello, 世界"
    , b64 = btoa(bin)
    ;

  console.log(b64); // "SGVsbG8sIBZM"
}());

Note: Unicode may or may not be handled incorrectly.