auto_link_urls.js

autoLinkUrls = (function() {
  /**
   * Converts urls starting with "www" or "http(s)" to clickable links
   *
   * Inspired by rails' "auto_link_urls" method
   * http://apidock.com/rails/ActionView/Helpers/TextHelper/auto_link_urls
   */
  var URL_REG_EXP           = /(https?:\/\/|www\.)[^\s<]+/gi,
      TRAILING_CHAR_REG_EXP = /([^\w\/-])$/i,
      MAX_DISPLAY_LENGTH    = 55,
      TRUNCATION            = "...",
      BRACKETS              = {
        ")": "(",
        "]": "[",
        "}": "{"
      };
  
  function truncate(url, maxLength) {
    return url.length > maxLength ? url.slice(0, maxLength - TRUNCATION.length) + TRUNCATION : url;
  }
  
  return function(str) {
    return str.replace(URL_REG_EXP, function(url) {
      var punctuation = (url.match(TRAILING_CHAR_REG_EXP) || [])[1] || "",
          opening     = BRACKETS[punctuation];
      
      url = url.replace(TRAILING_CHAR_REG_EXP, "");
      
      if (url.split(opening).length > url.split(punctuation).length) {
        url = url + punctuation;
        punctuation = "";
      }
      
      var realUrl    = url,
          displayUrl = truncate(url, MAX_DISPLAY_LENGTH);
      
      // Add http prefix if necessary
      if (realUrl.substr(0, 4) == "www.") {
        realUrl = "http://" + realUrl;
      }
      
      return '<a href="' + realUrl + '" target="_blank">' + displayUrl + '</a>' + punctuation;
    });
  };
})();