showdownjs/src/subParsers/autoLinks.js

// url allowed chars [a-z\d_.~:/?#[]@!$&'()*+,;=-]

var simpleURLRegex  = /\b(((https?|ftp|dict):\/\/|www\.)[^'">\s]+\.[^'">\s]+)()(?=\s|$)(?!["<>])/gi,
    simpleURLRegex2 = /\b(((https?|ftp|dict):\/\/|www\.)[^'">\s]+\.[^'">\s]+?)([.!?()]?)(?=\s|$)(?!["<>])/gi,
    //simpleURLRegex3 = /\b(((https?|ftp):\/\/|www\.)[a-z\d.-]+\.[a-z\d_.~:/?#\[\]@!$&'()*+,;=-]+?)([.!?()]?)(?=\s|$)(?!["<>])/gi,
    delimUrlRegex   = /<(((https?|ftp|dict):\/\/|www\.)[^'">\s]+)>/gi,
    simpleMailRegex = /(^|\s)(?:mailto:)?([A-Za-z0-9!#$%&'*+-/=?^_`{|}~.]+@[-a-z0-9]+(\.[-a-z0-9]+)*\.[a-z]+)(?=$|\s)/gmi,
    delimMailRegex  = /<()(?:mailto:)?([-.\w]+@[-a-z0-9]+(\.[-a-z0-9]+)*\.[a-z]+)>/gi,

    replaceLink = function (options) {
      'use strict';

      return function (wm, link, m2, m3, trailingPunctuation) {
        var lnkTxt = link,
            append = '';
        if (/^www\./i.test(link)) {
          link = link.replace(/^www\./i, 'http://www.');
        }
        if (options.excludeTrailingPunctuationFromURLs && trailingPunctuation) {
          append = trailingPunctuation;
        }
        return '<a href="' + link + '">' + lnkTxt + '</a>' + append;
      };
    },

    replaceMail = function (options, globals) {
      'use strict';
      return function (wholeMatch, b, mail) {
        var href = 'mailto:';
        b = b || '';
        mail = showdown.subParser('unescapeSpecialChars')(mail, options, globals);
        if (options.encodeEmails) {
          href = showdown.helper.encodeEmailAddress(href + mail);
          mail = showdown.helper.encodeEmailAddress(mail);
        } else {
          href = href + mail;
        }
        return b + '<a href="' + href + '">' + mail + '</a>';
      };
    };

showdown.subParser('autoLinks', function (text, options, globals) {
  'use strict';

  text = globals.converter._dispatch('autoLinks.before', text, options, globals);

  text = text.replace(delimUrlRegex, replaceLink(options));
  text = text.replace(delimMailRegex, replaceMail(options, globals));

  text = globals.converter._dispatch('autoLinks.after', text, options, globals);

  return text;
});

showdown.subParser('simplifiedAutoLinks', function (text, options, globals) {
  'use strict';

  if (!options.simplifiedAutoLink) {
    return text;
  }

  text = globals.converter._dispatch('simplifiedAutoLinks.before', text, options, globals);

  if (options.excludeTrailingPunctuationFromURLs) {
    text = text.replace(simpleURLRegex2, replaceLink(options));
  } else {
    text = text.replace(simpleURLRegex, replaceLink(options));
  }
  text = text.replace(simpleMailRegex, replaceMail(options, globals));

  text = globals.converter._dispatch('simplifiedAutoLinks.after', text, options, globals);

  return text;
});