title: How to fix Javascript NaN issue?
body: <p>Here is my code</p>
  
  <pre><code>  var total_center_buttons=$('.center_button').length;
    var center_button_height=$('.center_button:first-child').height();
    var total_center_button_height=total_center_buttons + center_button_height;
    alert(total_center_button_height);
  </code></pre>
  
  <p>Here <code>total_center_button value =3</code>
  and <code>center_button_height is 40</code> while alerting them separately.It returns <code>NaN</code>. I tried ParseInt also but result is same.Please suggest me the solution.<br><br>Thanks in advance.<br>
  Krishna</p>