title: Best way to return duplicate elements in an Array
body: <p>Here is the way I am using to return duplicate elements..  But I am facing most dangerous performance issues like browser close etc when my array have large number of items with long texts..  </p>
  
  <pre><code>var arr = [9, 9, 111, 2, 3, 4, 4, 5, 7];
  var sorted_arr = arr.sort();
  var results = [];
  for (var i = 0; i &lt; arr.length - 1; i++) {
    if (sorted_arr[i + 1] == sorted_arr[i]) {
       results.push(sorted_arr[i]);
    }
  }
  alert(results);
  </code></pre>
  
  <p>Please suggest me a best way of doing this  </p>