pure javascript implemented base64 encoding/decoding library.

b64.js

;
(
  function () {

    'use strict'

    var root = this
    var b64

    if (typeof exports !== 'undefined') {
      b64 = exports
    }
    else {
      b64 = root.b64 = {}
    }

    b64.VERSION = '0.0.1'

    var keyStr = b64.keyStr = "ABCDEFGHIJKLMNOP" +
      "QRSTUVWXYZabcdef" +
      "ghijklmnopqrstuv" +
      "wxyz0123456789+/" +
      "="

    var encode64 = b64.encode64 = function (input) {
      input = escape(input)
      var output = ""
      var chr1, chr2, chr3 = ""
      var enc1, enc2, enc3, enc4 = ""
      var i = 0

      do {
        chr1 = input.charCodeAt(i++)
        chr2 = input.charCodeAt(i++)
        chr3 = input.charCodeAt(i++)

        enc1 = chr1 >> 2
        enc2 = ((chr1 & 3) << 4) | (chr2 >> 4)
        enc3 = ((chr2 & 15) << 2) | (chr3 >> 6)
        enc4 = chr3 & 63

        if (isNaN(chr2)) {
          enc3 = enc4 = 64
        } else if (isNaN(chr3)) {
          enc4 = 64
        }

        output = output +
          keyStr.charAt(enc1) +
          keyStr.charAt(enc2) +
          keyStr.charAt(enc3) +
          keyStr.charAt(enc4)
        chr1 = chr2 = chr3 = ""
        enc1 = enc2 = enc3 = enc4 = ""
      } while (i < input.length)

      return output
    }

    var decode64 = b64.decode64 = function (input) {
      var output = ""
      var chr1, chr2, chr3 = ""
      var enc1, enc2, enc3, enc4 = ""
      var i = 0

      // remove all characters that are not A-Z, a-z, 0-9, +, /, or =
      var base64test = /[^A-Za-z0-9\+\/\=]/g
      if (base64test.exec(input)) {
        alert("There were invalid base64 characters in the input text.\n" +
              "Valid base64 characters are A-Z, a-z, 0-9, '+', '/',and '='\n" +
              "Expect errors in decoding.")
      }
      input = input.replace(/[^A-Za-z0-9\+\/\=]/g, "")

      do {
        enc1 = keyStr.indexOf(input.charAt(i++))
        enc2 = keyStr.indexOf(input.charAt(i++))
        enc3 = keyStr.indexOf(input.charAt(i++))
        enc4 = keyStr.indexOf(input.charAt(i++))

        chr1 = (enc1 << 2) | (enc2 >> 4)
        chr2 = ((enc2 & 15) << 4) | (enc3 >> 2)
        chr3 = ((enc3 & 3) << 6) | enc4

        output = output + String.fromCharCode(chr1)

        if (enc3 != 64) {
          output = output + String.fromCharCode(chr2)
        }
        if (enc4 != 64) {
          output = output + String.fromCharCode(chr3)
        }

        chr1 = chr2 = chr3 = ""
        enc1 = enc2 = enc3 = enc4 = ""

      } while (i < input.length)

      return unescape(output)
    }

  }

).call(this)
;

example.js

// example

var text = 'hello world! 你好! こんにちは！'

var encoded = b64.encode64(text)
console.log(encoded)                
// "aGVsbG8lMjB3b3JsZCUyMSUyMCV1NEY2MCV1NTk3RCUyMSUyMCV1MzA1MyV1MzA5MyV1MzA2QiV1MzA2MSV1MzA2RiV1RkYwMQ=="

var decoded = b64.decode64(encoded) 
console.log(decoded)                // 'hello world! 你好! こんにちは！'


// notice to export b64 when using with require.js.

thanks for this mate, I've modified this version with export default for my needed