title: node + mongo: updating a record requires a callback
body: <p>So I'm listening for an event with socket.io, once that fires I'm trying to update a record to a new value. </p>
  
  <pre><code>socket.on('contentEdited', function (newContent) {
  
  collection.update(
      { '_id' : ObjectId("5279262e74d92da751eb2b8e") }, 
      { $set: { 
        'content': newContent
        } 
      }
    ), function (err, result) {
      if (err) throw err;
      console.log(result)
    };
  
  });
  </code></pre>
  
  <p>The syntax works in the shell, but throws the following error in node when the event fires:</p>
  
  <blockquote>
    <p>Error: Cannot use a writeConcern without a provided callback</p>
  </blockquote>
  
  <p>I tried adding an function at the end afterwards for basic error checking, but I'm not sure how to provide a callback in the way mongo expects.</p>
  
  <p>Still kinda new to this, thanks</p>