title: Javascript: Add +1 to number that starts with 0 (like 01, 02, 03) and keep the zero
body: <p>I like to add (+1) to a number. But problem is my number can sometimes have 0 preceding it. Like 01, 02, 03, 04. So I like result to be:</p>
  
  <pre><code>mockup01 + 1 = mockup02
  mockup11 + 1 = mockup12
  </code></pre>
  
  <p>How can that be achieved? Example of how I would use it would be if I had filename named <strong>mockup_01.htm</strong> and change it to <strong>mockup_02.htm</strong></p>
  
  <p>Thanks!</p>