index.js

var shuffle = require('knuth-shuffle-seeded');

var chars_to_encode = "\"'~!@#$%^&*()<:>[]{}.,+=-ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";

var js_code_decode = "var d=function(b){var c=b.substring(0,"+chars_to_encode.length+");b=b.substring(c.length);var e,f,g,h='',d;for(e=0;e<b.length;e++)f=b.charAt(e),g=c.indexOf(f),d=(g-b.length+c.length)%c.length,d=0>d?c.length+d:d,h+=0<=g?c[d]:f;return h};";

var encode = function(text, seed){
  var key = shuffle(chars_to_encode.split(""), seed).join("");

  return key + text.split("").map(function(c){
    var i = key.indexOf(c);
    return i < 0 ? c : key[(i + text.length) % key.length];
  }).join('');
};

module.exports = function(html, seed){
  var id_i = 0;
  var inserts = {};
  html = html.split(/(<a href="mailto:(?:[^"]*)">(?:[^<]*)<\/a>)/gi).map(function(html_block, i){
      var matches = /^<a href="mailto:([^"]*)">(?:[^<]*)<\/a>$/gi.exec(html_block);
      if(matches && matches.length === 2){
        var email = matches[1];
        var id = 'droideka-' + id_i++;
        inserts[id] = '<a href="mailto:'+email+'">'+email+'</a>';
        return '<span id="'+id+'"><noscript>You must enable JavaScript to see the email.</noscript></span>';
      }
      return html_block;
  }).join('');
  if(Object.keys(inserts).length > 0){
    html += '<script type="application/javascript">';
    html += 'setTimeout(function(){';
    html += js_code_decode;
    html += Object.keys(inserts).map(function(id){
      var html = inserts[id];
      return '(function(){var a=document.getElementById("'+id+'");if(!a)return;a.innerHTML=d('+JSON.stringify(encode(html, seed))+');}());';
    }).join('');
    html += '}, 500);';
    html += '</script>';
  }
  return html;
};
module.exports.encode = encode;
module.exports.js_code_decode = js_code_decode;