title: Can someone explan this error: expression statement is not assignment or call
body: <p>I have these two blocks of code.</p>
  
  <pre><code>socket.on('chatMessage', function(message) {
      message.type = 'message';
      message.created = Date.now();
      message.username : socket.request.user.username;
  });
  
  socket.on('disconnect', function() {
      io.emit('chatMessage', {
          type: 'status',
          text: socket.request.user.username + ' left the conversation.',
          created: Date.now(),
          username: socket.request.user.username,
      });
  });
  </code></pre>
  
  <p>If i change <code>:</code> or <code>=</code> to other, Webstorm gives me error.<code>Expression statement is not assignment or call.</code> Could someone explain why this happens?  Thanks in advance.</p>