title: JavaScript Calculate expression in octal radix
body: <p>For example, I have the following string:</p>
  
  <pre><code>15+6
  </code></pre>
  
  <p>I want to calculate this expression in octal radix. So I want to get:</p>
  
  <pre><code>23
  </code></pre>
  
  <p>Is there any function in js to support this case? If not, what is the best approach to calculate octal expression?</p>