showdown/src/subParsers/encodeEmailAddress.js

/**
 *  Input: an email address, e.g. "foo@example.com"
 *
 *  Output: the email address as a mailto link, with each character
 *    of the address encoded as either a decimal or hex entity, in
 *    the hopes of foiling most address harvesting spam bots. E.g.:
 *
 *    <a href="&#x6D;&#97;&#105;&#108;&#x74;&#111;:&#102;&#111;&#111;&#64;&#101;
 *       x&#x61;&#109;&#x70;&#108;&#x65;&#x2E;&#99;&#111;&#109;">&#102;&#111;&#111;
 *       &#64;&#101;x&#x61;&#109;&#x70;&#108;&#x65;&#x2E;&#99;&#111;&#109;</a>
 *
 *  Based on a filter by Matthew Wickline, posted to the BBEdit-Talk
 *  mailing list: <http://tinyurl.com/yu7ue>
 *
 */
showdown.subParser('encodeEmailAddress', function (addr) {
  'use strict';

  var encode = [
    function (ch) {
      return '&#' + ch.charCodeAt(0) + ';';
    },
    function (ch) {
      return '&#x' + ch.charCodeAt(0).toString(16) + ';';
    },
    function (ch) {
      return ch;
    }
  ];

  addr = 'mailto:' + addr;

  addr = addr.replace(/./g, function (ch) {
    if (ch === '@') {
      // this *must* be encoded. I insist.
      ch = encode[Math.floor(Math.random() * 2)](ch);
    } else if (ch !== ':') {
      // leave ':' alone (to spot mailto: later)
      var r = Math.random();
      // roughly 10% raw, 45% hex, 45% dec
      ch = (
        r > 0.9 ? encode[2](ch) : r > 0.45 ? encode[1](ch) : encode[0](ch)
      );
    }
    return ch;
  });

  addr = '<a href="' + addr + '">' + addr + '</a>';
  addr = addr.replace(/">.+:/g, '">'); // strip the mailto: from the visible part

  return addr;
});