Regular Expressions with Named Groups

regex-named-groups.js

/**
 * Allows you to specify named groups in regular expressions like in Perl/Python/.NET/etc. You have to
 * use a string to specify the regex, and the function returns an object that has `exec` and `replace`
 * functions like a normal RegExp object, but matches they generate have keys for the values of the named
 * groups.
 * 
 * n = NamedRegExp("(?<protocol>http|ftp)://(?<host>[\\w-]+\\.com)(?<path>/.+\\.html)?$");
 * res = n.exec("http://foobar.com"); -> res.protocol = http, res.host = foobar.com res.path = undefined
 * res = n.exec("http://foobar.com/"); -> res.protocol = http, res.host = foobar.com res.path = /
 * res = n.exec("http://foobar.com/index.html"); -> res.protocol = http, res.host = foobar.com res.path = /index.html
 *
 * n = NamedRegExp("(?<initial>[A-Z]) (?<surname>[A-Z][a-zA-Z]+)")
 * n.replace("J Skinner, M Cow and F Baloney", function(m) {
 *   return m.surname + ", " + m.initial + ".";
 * }) -> "Skinner, J., Cow M. and Baloney, F."
 * 
 * @param {String} regex_str
 * @param {String?} flags
 * @return {NamedRegExp}
 */
function NamedRegExp(regex_str, flags) {
  var
    name_order = [null],

    plain_regex = regex_str.replace(/\(\?<(\w+)>/g, function(match, name) {
      var i = name_order.indexOf(name);
      if (i == -1) {
        i = name_order.push(name);
      }
      return "(";
    }),

    matches_extend = function(matches) {
      if (matches) {
        for (var i = 1; i < matches.length; i++) {
          matches[name_order[i]] = matches[i];
        }
      }
      return matches;
    };

  return {
    exec: function(src) {
      var
        re = RegExp(plain_regex, flags),
        matches = re.exec(src);
      return matches_extend(matches);
    },

    replace: function(src, repl_func) {
      var re = RegExp(plain_regex, "g" + flags);

      return src.replace(re, function() {
        var match = matches_extend(Array.from(arguments).slice(0, -2));
        //console.dir(arguments);
        return repl_func(match);
      });
    }
  };
}



// --------------------------------------------------------------------

/**
 * array_to_obj([1, 5, 6], "x y z") -> { x: 1, y: 5, z: 6 }
 * array_to_obj([undefined, 4], ["score", "level"]) -> { level: 4 }
 */
function arr_to_obj(arr, names) {
  var keys = Array.isArray(names) ? names : names.split(" "),
    obj = {},
    i = 0;

  if (arr.length > keys.length) {
    throw Error("Not enough key names!");
  }

  for (; i < keys.length; i++) {
    if (typeof arr[i] !== "undefined") {
      obj[keys[i]] = arr[i];
    }
  }

  return obj;
}