getting how many people are in a chat room in socket.io

If you're using version < 1,

var clients = io.sockets.clients(nick.room); // all users from room

For socket.io versions >= 1.0:

Note that rooms became actual types with a .length property in 1.4, so the 1.4.x method should be stable from now on. Barring breaking changes to that type's API, of course.

To count all clients connected to 'my_room':

1.4+:

var room = io.sockets.adapter.rooms['my_room'];
room.length;

1.3.x:

var room = io.sockets.adapter.rooms['my_room'];
Object.keys(room).length;

1.0.x to 1.2.x:

var room = io.adapter.rooms['my_room'];
Object.keys(room).length;

This is assuming you're running with the default room adapter on a single node (as opposed to a cluster). Things are more complicated if you're in a cluster.

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Other related examples:

• Count all clients connected to server:

  var srvSockets = io.sockets.sockets;
  Object.keys(srvSockets).length;
  

• Count all clients connected to namespace '/chat':

  var nspSockets = io.of('/chat').sockets;
  Object.keys(nspSockets).length