simple base64 encode relied on window.btoa

base64encode.js

function base64Encode( str ) {
  str = str.replace( /[^\x00-\x7F]/g, function ( char ) {
      var hex = char.charCodeAt( 0 ).toString( 16 );
      while ( hex.length < 4 ) hex = '0' + hex;

      return '\\u' + hex;
  });

  return btoa( str );
}