title: replace all characters in string except last 4 characters
body: <p>Using Go, how do I replace all characters in a string with "X" except the last 4 characters?</p>
  
  <p>This works fine for php/javascript but not for golang as "?=" is not supported.</p>
  
  <pre><code>\w(?=\w{4,}$)
  </code></pre>
  
  <p>Tried this, but does not work. I couldn't find anything similar for golang</p>
  
  <pre><code>(\w)(?:\w{4,}$)
  </code></pre>
  
  <p><a href="https://regex101.com/r/bxknUH/2" rel="nofollow noreferrer">JavaScript working link</a></p>
  
  <p><a href="https://regex101.com/r/T5ntlg/3" rel="nofollow noreferrer">Go non-working link</a></p>