title: Validate jquery regex - number start with 931
body: <p>I need to validate number that use inputs into input box.
  Number must be exactly 12 characters long and start with 931.</p>
  
  <pre><code>var reg = /^931[0-9]$/;
  var val = $("#sms_number").val();
  
  if (val.length === 12 &amp;&amp; reg.test(val)) {                    
  
  
  }
  </code></pre>
  
  <p>Above is incorrect.</p>