Javascript Base64 singleton

Similar to the javascript MD5 singleton micro-lib I wrapped up some time ago (source code), here is an even tinier Base64.encode / Base64.decode singleton (source code) I reworked from Tyler Akins' public domain original. Absolutely no error handling or recovery in this variant, so don't pass anything but eight-bit data to Base64.encode, nor correct base64 data to Base64.decode.

// Based on public domain code by Tyler Akins <http://rumkin.com/>
// Original code at http://rumkin.com/tools/compression/base64.php

var Base64 = (function() {
  function encode_base64(data) {
    var out = "", c1, c2, c3, e1, e2, e3, e4;
    for (var i = 0; i < data.length; ) {
       c1 = data.charCodeAt(i++);
       c2 = data.charCodeAt(i++);
       c3 = data.charCodeAt(i++);
       e1 = c1 >> 2;
       e2 = ((c1 & 3) << 4) + (c2 >> 4);
       e3 = ((c2 & 15) << 2) + (c3 >> 6);
       e4 = c3 & 63;
       if (isNaN(c2))
         e3 = e4 = 64;
       else if (isNaN(c3))
         e4 = 64;
       out += tab.charAt(e1) + tab.charAt(e2) + tab.charAt(e3) + tab.charAt(e4);
    }
    return out;
  }

  function decode_base64(data) {
    var out = "", c1, c2, c3, e1, e2, e3, e4;
    for (var i = 0; i < data.length; ) {
      e1 = tab.indexOf(data.charAt(i++));
      e2 = tab.indexOf(data.charAt(i++));
      e3 = tab.indexOf(data.charAt(i++));
      e4 = tab.indexOf(data.charAt(i++));
      c1 = (e1 << 2) + (e2 >> 4);
      c2 = ((e2 & 15) << 4) + (e3 >> 2);
      c3 = ((e3 & 3) << 6) + e4;
      out += String.fromCharCode(c1);
      if (e3 != 64)
        out += String.fromCharCode(c2);
      if (e4 != 64)
        out += String.fromCharCode(c3);
    }
    return out;
  }

  var tab = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";
  return { encode:encode_base64, decode:decode_base64 };
})();