(function() {

  var str = "Hi there @john, it's @mary, my email is mary@example.com.";

  var re = /\B@(\w+)/g;

  var m;

  for (m = re.exec(str); m; m = re.exec(str)) {

    display("Found: " + m[1]);

  }

  function display(msg) {

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

    p.innerHTML = String(msg);

    document.body.appendChild(p);

  }

})();