title: String: Masking last n characters with * sign
body: <p>I have a following string:</p>
  
  <pre><code>99001155
  </code></pre>
  
  <p>I want to mask last 4 characters with <code>*</code> sign. For example:</p>
  
  <blockquote>
    <p>99001155 -> 9900****</p>
  </blockquote>
  
  <p>How to do that?</p>