title: JavaScript regular expression exception (Invalid group)
body: <p>I have the following regular expression:</p>
  
  <pre><code>/(?&lt;={index:)\d+(?=})/g
  </code></pre>
  
  <p>I am trying to find index integer in strings like this one:</p>
  
  <pre><code>some text{index:1}{id:2}{value:3}
  </code></pre>
  
  <p>That expression works fine with php, but it doesn't work in javascript, I get the following error:</p>
  
  <blockquote>
    <p>Uncaught SyntaxError: Invalid regular
    expression: /(?&lt;={index:)\d+(?=})/:
    Invalid group</p>
  </blockquote>
  
  <p>What do I need to fix?</p>
  
  <p>Thanks.</p>