title: Error using both lookahead and look behind regex
body: <p>I am having a problem using the following regex. It works fine in regexr and rubular but it gives me an error when running it on node.js. I am fairly new to using regex and i'm not sure what i'm doing wrong. It will work if I knock off the <code>(?&lt;= )</code> so I presume that is the problem.</p>
  
  <p>I'm trying to match 'is' with a leading and trailing space using <code>/(?&lt;= )is(?= )|==/g</code></p>
  
  <p>Example with test words:<br>
  <a href="http://regexr.com?33781" rel="noreferrer">http://regexr.com?33781</a></p>
  
  <p>Node error output  </p>
  
  <pre><code> temp = temp.replace(/(?&lt;= )is(?= )|==/g, '===');
  ^
  SyntaxError: Invalid regular expression: /(?&lt;= )is(?= )|==/: Invalid group
  at new RegExp (unknown source)
  </code></pre>