(function() {

  var str = "this is a this test test";

  var index;

  var matches = str.match(/\w+(\s+\w+)*/)(?=.*\1)/);

  if (matches) {

    display("Found " + matches.length + ":");

    for (index = 0; index < matches.length; ++index) {

      display("[" + index + "]: " + matches[index]);

    }

  }

  else {

    display("No matches found");

  }

  function display(msg) {

    var p = document.createElement('p');

    p.innerHTML = String(msg);

    document.body.appendChild(p);

  }

})();