title: RegEx for single asterisk (*) and alphanumeric
body: <p>I need a javascript regex that accepts any alphanumeric character (can be any amount of characters or 0 characters if an asterisk is present) and a single asterisk anywhere in the string (but it does not need the asterisk).</p>
  
  <p><strong>Matches</strong></p>
  
  <pre><code>*
  abc
  *abc
  abc*
  a*bc
  </code></pre>
  
  <p><strong>Invalid Matches</strong></p>
  
  <pre><code>**
  *_abc
  *abc*
  abc**
  **abc
  </code></pre>
  
  <p>I have </p>
  
  <pre><code>^([A-Za-z\d*]?)+$ 
  </code></pre>
  
  <p>but that matches multiple asterisks and I'm not sure how to only allow one <a href="https://regex101.com/r/a1C9bf/1" rel="nofollow noreferrer">https://regex101.com/r/a1C9bf/1</a></p>