title: concat variable in regexp pattern
body: <p>I use this regex</p>
  
  <pre><code>str = "asd34rgr888gfd98";
  var p = str.match(/\d{2}/);
  alert(p[0]);
  </code></pre>
  
  <p>butI not understood how can use variable as quantificator, that is how write this:</p>
  
  <pre><code> var number = 2;
   var p = str.match(/\d{number}/);
  </code></pre>
  
  <p>P.S. I see this page <a href="https://stackoverflow.com/questions/2712878/javascript-regex-pattern-concatenate-with-variable">JavaScript regex pattern concatenate with variable</a> 
  but not understood how use example from these posts, in my case.</p>