title: regex to allow one comma and not at the start or end of string in JavaScript
body: <p>I am not very good at regex and I need 3 different regex's that follow the following rules:</p>
  
  <ol>
  <li>I need a regex that only allows one comma in string</li>
  <li>I need a regex that doesn't allow a comma at the start of a string but still allow only one comma.</li>
  <li>I need a regex that doesn't allow a comma at the end of a string but still allow only one comma.</li>
  </ol>
  
  <p>For the first rule: <code>21, day</code> would be okay but <code>21, day, 32</code> would not be okay.</p>
  
  <p>For the second rule: <code>,21</code> would not be okay.</p>
  
  <p>For the third rule: <code>21,</code> would not be okay.</p>
  
  <p>So far I have created a regex below which accommodates for the rules above but I was wondering if it could be split up into three different regex's that can accommodate for the three above rules.</p>
  
  <pre><code>^[a-z0-9A-Z&amp;.\/'_ ]+(,[a-zA-Z0-9&amp;.\/'_ ]+)?$
  </code></pre>
  
  <p>Any help would be much appreciated.
  Thanks</p>