Socket.io: how to clear the room ?

@wendux rooms are created and deleted automatically. That means when the room is empty, there are no more clients left on it, it will be deleted.
You can do this to remove all clients from a room:

io.of('/').in('chat').clients((error, socketIds) => {
  if (error) throw error;

  socketIds.forEach(socketId => io.sockets.sockets[socketId].leave('chat'));

});

https://socket.io/docs/server-api/#namespace-clients-callback

To complete @rllalloshi's answer, in a multi-server configuration you should use the removeLeave method of the adapter:

io.of('/').in('chat').clients((error, socketIds) => {
  if (error) throw error;

  socketIds.forEach(socketId => io.of('/').adapter.remoteLeave(socketId, 'chat'));

});

Reference

@wendux rooms are created and deleted automatically. That means when the room is empty, there are no more clients left on it, it will be deleted.
You can do this to remove all clients from a room:

io.of('/').in('chat').clients((error, socketIds) => {
  if (error) throw error;

  socketIds.forEach(socketId => io.sockets.sockets[socketId].leave('chat'));

});

https://socket.io/docs/server-api/#namespace-clients-callback

it did not work in socket.io 2.2.0

Why is there no simple call to remove all sockets from a room? It is a very common use case

i vote to add. room.kick() function where you can pass in a specific id, an array, or 'ALL" for removing everyone