title: NodeJS mongoClient invalid operator: $eq
body: <p>I have a mongo property (category), where I want to filter with equals.
  I used the following syntax:</p>
  
  <pre><code>{"category":{"$eq":"cat1"}}
  </code></pre>
  
  <p>(I know, it can be written like:</p>
  
  <pre><code>{"category":"cat1"}
  </code></pre>
  
  <p>If I use the $eq operator, the mongoClient fails with "invalid operator: $eq". But only on localhost.
  If I deploy the same code to a remote server, it works perfectly.</p>
  
  <p>How can I make it work on localhost?
  It would be preferred to use the $eq operator - there are many places in the code where this is used.</p>
  
  <p>Thx</p>