Just run the sample app, and you'll see a few console errors.
Complete console logs
[Error] TypeError: Type error
send (socketcluster.js, line 940)
_send (socketcluster.js, line 940)
_sendObject (socketcluster.js, line 945)
_emitRaw (socketcluster.js, line 969)
_emitDirect (socketcluster.js, line 1018)
_trySubscribe (socketcluster.js, line 1115)
(anonymous function) (socketcluster.js, line 1263)
_resubscribe (socketcluster.js, line 1265)
_onSCOpen (socketcluster.js, line 582)
onopen (socketcluster.js, line 543)
[Error] Failed to load resource: the server responded with a status of 404 (Not Found) (favicon.ico, line 0)
[Log] RANDOM: 1 :D (127.0.0.1, line 33)
[Log] RANDOM: 2 :) (127.0.0.1, line 33)
[Log] RANDOM: 4 ;) (127.0.0.1, line 33)
[Error] TypeError: Type error
send (socketcluster.js, line 940)
_send (socketcluster.js, line 940)
_sendObject (socketcluster.js, line 945)
sendObject (socketcluster.js, line 953)
disconnect (socketcluster.js, line 560)
unloadHandler (socketcluster.js, line 458)
[Error] TypeError: Type error
send (socketcluster.js, line 940)
_send (socketcluster.js, line 940)
_sendObject (socketcluster.js, line 945)
_emitRaw (socketcluster.js, line 969)
_emitDirect (socketcluster.js, line 1018)
_trySubscribe (socketcluster.js, line 1115)
(anonymous function) (socketcluster.js, line 1263)
_resubscribe (socketcluster.js, line 1265)
_onSCOpen (socketcluster.js, line 582)
onopen (socketcluster.js, line 543)
[Log] RANDOM: 3 :3 (127.0.0.1, line 33)
[Log] RANDOM: 4 ;) (127.0.0.1, line 33)
[Log] RANDOM: 2 :) (127.0.0.1, line 33)
[Log] RANDOM: 0 ;p (127.0.0.1, line 33, x2)
[Log] RANDOM: 3 :3 (127.0.0.1, line 33)
[Log] RANDOM: 2 :) (127.0.0.1, line 33)
[Log] RANDOM: 3 :3 (127.0.0.1, line 33)
[Log] RANDOM: 2 :) (127.0.0.1, line 33)
[Error] ReferenceError: Can't find variable: callback
_handleEventAckTimeout (socketcluster.js, line 996)
(anonymous function) (socketcluster.js, line 1013)
[Log] RANDOM: 1 :D (127.0.0.1, line 33)
[Log] RANDOM: 0 ;p (127.0.0.1, line 33)
[Log] RANDOM: 2 :) (127.0.0.1, line 33)
[Error] TypeError: Type error
send (socketcluster.js, line 940)
_send (socketcluster.js, line 940)
_sendObject (socketcluster.js, line 945)
sendObject (socketcluster.js, line 953)
disconnect (socketcluster.js, line 560)
unloadHandler (socketcluster.js, line 458)
[Log] RANDOM: 3 :3 (127.0.0.1, line 33)
[Error] TypeError: Type error
send (socketcluster.js, line 940)
_send (socketcluster.js, line 940)
_sendObject (socketcluster.js, line 945)
_emitRaw (socketcluster.js, line 969)
_emitDirect (socketcluster.js, line 1018)
_trySubscribe (socketcluster.js, line 1115)
(anonymous function) (socketcluster.js, line 1263)
_resubscribe (socketcluster.js, line 1265)
_onSCOpen (socketcluster.js, line 582)
onopen (socketcluster.js, line 543)
[Log] RANDOM: 1 :D (127.0.0.1, line 33)
[Log] RANDOM: 4 ;) (127.0.0.1, line 33)
[Log] RANDOM: 2 :) (127.0.0.1, line 33, x2)
[Log] RANDOM: 3 :3 (127.0.0.1, line 33)
[Log] RANDOM: 1 :D (127.0.0.1, line 33, x3)
[Log] RANDOM: 2 :) (127.0.0.1, line 33)
[Error] ReferenceError: Can't find variable: callback
_handleEventAckTimeout (socketcluster.js, line 996)
(anonymous function) (socketcluster.js, line 1013)
[Log] RANDOM: 2 :) (127.0.0.1, line 33)
[Log] RANDOM: 3 :3 (127.0.0.1, line 33)
[Log] RANDOM: 1 :D (127.0.0.1, line 33, x2)
[Log] RANDOM: 4 ;) (127.0.0.1, line 33)
[Log] RANDOM: 1 :D (127.0.0.1, line 33)
[Log] RANDOM: 0 ;p (127.0.0.1, line 33)
[Log] RANDOM: 2 :) (127.0.0.1, line 33)
[Log] RANDOM: 3 :3 (127.0.0.1, line 33)
[Log] RANDOM: 1 :D (127.0.0.1, line 33, x2)
[Log] RANDOM: 2 :) (127.0.0.1, line 33)
[Log] RANDOM: 4 ;) (127.0.0.1, line 33, x2)
[Log] RANDOM: 1 :D (127.0.0.1, line 33)
[Error] TypeError: Type error
send (socketcluster.js, line 940)
_send (socketcluster.js, line 940)
send (socketcluster.js, line 949)
_onSCMessage (socketcluster.js, line 732)
onmessage (socketcluster.js, line 551)
[Log] RANDOM: 2 :) (127.0.0.1, line 33, x2)
[Log] RANDOM: 4 ;) (127.0.0.1, line 33)
[Log] RANDOM: 2 :) (127.0.0.1, line 33, x3)
[Log] RANDOM: 1 :D (127.0.0.1, line 33)
[Log] RANDOM: 4 ;) (127.0.0.1, line 33)
[Log] RANDOM: 2 :) (127.0.0.1, line 33)
[Log] RANDOM: 1 :D (127.0.0.1, line 33)
[Log] RANDOM: 0 ;p (127.0.0.1, line 33)
[Log] RANDOM: 2 :) (127.0.0.1, line 33)
[Log] RANDOM: 1 :D (127.0.0.1, line 33)
[Log] RANDOM: 4 ;) (127.0.0.1, line 33)
[Log] RANDOM: 1 :D (127.0.0.1, line 33, x3)
[Log] RANDOM: 0 ;p (127.0.0.1, line 33)
[Log] RANDOM: 1 :D (127.0.0.1, line 33, x2)
[Log] RANDOM: 3 :3 (127.0.0.1, line 33)
[Log] RANDOM: 0 ;p (127.0.0.1, line 33)
[Log] RANDOM: 4 ;) (127.0.0.1, line 33, x2)
[Log] RANDOM: 2 :) (127.0.0.1, line 33)
[Error] TypeError: Type error
send (socketcluster.js, line 940)
_send (socketcluster.js, line 940)
send (socketcluster.js, line 949)
_onSCMessage (socketcluster.js, line 732)
onmessage (socketcluster.js, line 551)
[Log] RANDOM: 3 :3 (127.0.0.1, line 33)
[Log] RANDOM: 4 ;) (127.0.0.1, line 33)
[Log] RANDOM: 0 ;p (127.0.0.1, line 33, x2)
[Log] RANDOM: 1 :D (127.0.0.1, line 33)
[Log] RANDOM: 4 ;) (127.0.0.1, line 33)
[Log] RANDOM: 1 :D (127.0.0.1, line 33, x2)
[Log] RANDOM: 2 :) (127.0.0.1, line 33)
[Log] RANDOM: 1 :D (127.0.0.1, line 33)
[Error] Socket error - Error: Client pong timed out
(anonymous function) (127.0.0.1, line 18)
emit (socketcluster.js, line 1419)
(anonymous function) (socketcluster.js, line 632)
[Error] TypeError: Type error
send (socketcluster.js, line 940)
_send (socketcluster.js, line 940)
_sendObject (socketcluster.js, line 945)
_emitRaw (socketcluster.js, line 969)
_emitDirect (socketcluster.js, line 1018)
_trySubscribe (socketcluster.js, line 1115)
(anonymous function) (socketcluster.js, line 1263)
_resubscribe (socketcluster.js, line 1265)
_onSCOpen (socketcluster.js, line 582)
onopen (socketcluster.js, line 543)
[Log] RANDOM: 0 ;p (127.0.0.1, line 33)
[Log] RANDOM: 4 ;) (127.0.0.1, line 33)
[Log] RANDOM: 0 ;p (127.0.0.1, line 33)
[Log] RANDOM: 2 :) (127.0.0.1, line 33)
[Log] RANDOM: 3 :3 (127.0.0.1, line 33)
[Log] RANDOM: 0 ;p (127.0.0.1, line 33)
[Log] RANDOM: 3 :3 (127.0.0.1, line 33)
[Log] RANDOM: 2 :) (127.0.0.1, line 33)
[Log] RANDOM: 4 ;) (127.0.0.1, line 33)
[Error] ReferenceError: Can't find variable: callback
_handleEventAckTimeout (socketcluster.js, line 996)
(anonymous function) (socketcluster.js, line 1013)
[Log] RANDOM: 1 :D (127.0.0.1, line 33, x2)
[Log] RANDOM: 0 ;p (127.0.0.1, line 33)
[Log] RANDOM: 4 ;) (127.0.0.1, line 33)
[Log] RANDOM: 1 :D (127.0.0.1, line 33)
[Log] RANDOM: 3 :3 (127.0.0.1, line 33)
[Log] RANDOM: 0 ;p (127.0.0.1, line 33, x2)
[Log] RANDOM: 4 ;) (127.0.0.1, line 33)
[Log] RANDOM: 2 :) (127.0.0.1, line 33)
[Log] RANDOM: 4 ;) (127.0.0.1, line 33)
[Log] RANDOM: 2 :) (127.0.0.1, line 33)
[Log] RANDOM: 3 :3 (127.0.0.1, line 33)
[Log] RANDOM: 1 :D (127.0.0.1, line 33)
[Log] RANDOM: 3 :3 (127.0.0.1, line 33)
[Error] TypeError: Type error
send (socketcluster.js, line 940)
_send (socketcluster.js, line 940)
send (socketcluster.js, line 949)
_onSCMessage (socketcluster.js, line 732)
onmessage (socketcluster.js, line 551)
[Log] RANDOM: 0 ;p (127.0.0.1, line 33)
[Log] RANDOM: 3 :3 (127.0.0.1, line 33)
[Log] RANDOM: 2 :) (127.0.0.1, line 33)
[Log] RANDOM: 4 ;) (127.0.0.1, line 33)
[Log] RANDOM: 0 ;p (127.0.0.1, line 33)
[Log] RANDOM: 1 :D (127.0.0.1, line 33)
[Log] RANDOM: 2 :) (127.0.0.1, line 33)
[Log] RANDOM: 4 ;) (127.0.0.1, line 33)
[Log] RANDOM: 3 :3 (127.0.0.1, line 33, x2)
[Log] RANDOM: 2 :) (127.0.0.1, line 33)
[Log] RANDOM: 3 :3 (127.0.0.1, line 33)
[Log] RANDOM: 0 ;p (127.0.0.1, line 33)
[Log] RANDOM: 4 ;) (127.0.0.1, line 33)
[Log] RANDOM: 2 :) (127.0.0.1, line 33, x2)
[Log] RANDOM: 0 ;p (127.0.0.1, line 33)
[Log] RANDOM: 1 :D (127.0.0.1, line 33)
[Log] RANDOM: 0 ;p (127.0.0.1, line 33)
[Log] RANDOM: 3 :3 (127.0.0.1, line 33)
[Log] RANDOM: 4 ;) (127.0.0.1, line 33)
[Log] RANDOM: 0 ;p (127.0.0.1, line 33)
[Log] RANDOM: 4 ;) (127.0.0.1, line 33, x2)
[Log] RANDOM: 3 :3 (127.0.0.1, line 33)
[Error] TypeError: Type error
send (socketcluster.js, line 940)
_send (socketcluster.js, line 940)
send (socketcluster.js, line 949)
_onSCMessage (socketcluster.js, line 732)
onmessage (socketcluster.js, line 551)
[Log] RANDOM: 4 ;) (127.0.0.1, line 33)
[Log] RANDOM: 3 :3 (127.0.0.1, line 33)
[Log] RANDOM: 1 :D (127.0.0.1, line 33)
[Log] RANDOM: 2 :) (127.0.0.1, line 33)
[Log] RANDOM: 1 :D (127.0.0.1, line 33)
[Log] RANDOM: 4 ;) (127.0.0.1, line 33)
[Log] RANDOM: 1 :D (127.0.0.1, line 33)
[Log] RANDOM: 4 ;) (127.0.0.1, line 33)
[Log] RANDOM: 3 :3 (127.0.0.1, line 33)
[Log] RANDOM: 0 ;p (127.0.0.1, line 33)
[Error] Socket error - Error: Client pong timed out
(anonymous function) (127.0.0.1, line 18)
emit (socketcluster.js, line 1419)
(anonymous function) (socketcluster.js, line 632)
[Error] TypeError: Type error
send (socketcluster.js, line 940)
_send (socketcluster.js, line 940)
_sendObject (socketcluster.js, line 945)
_emitRaw (socketcluster.js, line 969)
_emitDirect (socketcluster.js, line 1018)
_trySubscribe (socketcluster.js, line 1115)
(anonymous function) (socketcluster.js, line 1263)
_resubscribe (socketcluster.js, line 1265)
_onSCOpen (socketcluster.js, line 582)
onopen (socketcluster.js, line 543)
[Log] RANDOM: 2 :) (127.0.0.1, line 33, x2)
[Log] RANDOM: 4 ;) (127.0.0.1, line 33, x2)
[Log] RANDOM: 2 :) (127.0.0.1, line 33)
[Log] RANDOM: 0 ;p (127.0.0.1, line 33)
[Log] RANDOM: 1 :D (127.0.0.1, line 33)
[Log] RANDOM: 0 ;p (127.0.0.1, line 33)
[Log] RANDOM: 2 :) (127.0.0.1, line 33)
[Error] ReferenceError: Can't find variable: callback
_handleEventAckTimeout (socketcluster.js, line 996)
(anonymous function) (socketcluster.js, line 1013)
[Log] RANDOM: 4 ;) (127.0.0.1, line 33)
[Log] RANDOM: 2 :) (127.0.0.1, line 33, x4)
[Log] RANDOM: 1 :D (127.0.0.1, line 33)
[Log] RANDOM: 3 :3 (127.0.0.1, line 33)
[Log] RANDOM: 2 :) (127.0.0.1, line 33, x2)
[Log] RANDOM: 4 ;) (127.0.0.1, line 33)
[Log] RANDOM: 0 ;p (127.0.0.1, line 33)
[Log] RANDOM: 2 :) (127.0.0.1, line 33)
[Log] RANDOM: 1 :D (127.0.0.1, line 33)
[Log] RANDOM: 3 :3 (127.0.0.1, line 33)
[Log] RANDOM: 0 ;p (127.0.0.1, line 33)
[Error] TypeError: Type error
send (socketcluster.js, line 940)
_send (socketcluster.js, line 940)
send (socketcluster.js, line 949)
_onSCMessage (socketcluster.js, line 732)
onmessage (socketcluster.js, line 551)
[Log] RANDOM: 0 ;p (127.0.0.1, line 33)
[Log] RANDOM: 1 :D (127.0.0.1, line 33)
[Log] RANDOM: 4 ;) (127.0.0.1, line 33)
[Log] RANDOM: 0 ;p (127.0.0.1, line 33, x3)
[Log] RANDOM: 3 :3 (127.0.0.1, line 33, x2)
[Log] RANDOM: 1 :D (127.0.0.1, line 33, x2)
[Log] RANDOM: 0 ;p (127.0.0.1, line 33)
[Log] RANDOM: 4 ;) (127.0.0.1, line 33)
[Log] RANDOM: 1 :D (127.0.0.1, line 33)
[Log] RANDOM: 3 :3 (127.0.0.1, line 33)
[Log] RANDOM: 2 :) (127.0.0.1, line 33)
[Log] RANDOM: 1 :D (127.0.0.1, line 33, x2)
[Log] RANDOM: 4 ;) (127.0.0.1, line 33, x2)
[Log] RANDOM: 1 :D (127.0.0.1, line 33, x3)
[Log] RANDOM: 3 :3 (127.0.0.1, line 33)
[Log] RANDOM: 0 ;p (127.0.0.1, line 33)
[Log] RANDOM: 4 ;) (127.0.0.1, line 33)
[Error] TypeError: Type error
send (socketcluster.js, line 940)
_send (socketcluster.js, line 940)
send (socketcluster.js, line 949)
_onSCMessage (socketcluster.js, line 732)
onmessage (socketcluster.js, line 551)
[Log] RANDOM: 0 ;p (127.0.0.1, line 33)
[Log] RANDOM: 3 :3 (127.0.0.1, line 33)
[Log] RANDOM: 4 ;) (127.0.0.1, line 33)
[Log] RANDOM: 2 :) (127.0.0.1, line 33)
[Log] RANDOM: 3 :3 (127.0.0.1, line 33, x3)
[Log] RANDOM: 2 :) (127.0.0.1, line 33)
[Log] RANDOM: 0 ;p (127.0.0.1, line 33)
[Log] RANDOM: 4 ;) (127.0.0.1, line 33)
[Error] Socket error - Error: Client pong timed out
(anonymous function) (127.0.0.1, line 18)
emit (socketcluster.js, line 1419)
(anonymous function) (socketcluster.js, line 632)
[Error] TypeError: Type error
send (socketcluster.js, line 940)
_send (socketcluster.js, line 940)
_sendObject (socketcluster.js, line 945)
_emitRaw (socketcluster.js, line 969)
_emitDirect (socketcluster.js, line 1018)
_trySubscribe (socketcluster.js, line 1115)
(anonymous function) (socketcluster.js, line 1263)
_resubscribe (socketcluster.js, line 1265)
_onSCOpen (socketcluster.js, line 582)
onopen (socketcluster.js, line 543)
[Log] RANDOM: 4 ;) (127.0.0.1, line 33, x2)
[Log] RANDOM: 2 :) (127.0.0.1, line 33)
[Log] RANDOM: 3 :3 (127.0.0.1, line 33)
[Log] RANDOM: 2 :) (127.0.0.1, line 33)
[Log] RANDOM: 3 :3 (127.0.0.1, line 33)
[Log] RANDOM: 0 ;p (127.0.0.1, line 33, x2)
[Log] RANDOM: 2 :) (127.0.0.1, line 33)
[Error] ReferenceError: Can't find variable: callback
_handleEventAckTimeout (socketcluster.js, line 996)
(anonymous function) (socketcluster.js, line 1013)
[Log] RANDOM: 2 :) (127.0.0.1, line 33)
[Log] RANDOM: 1 :D (127.0.0.1, line 33)
[Log] RANDOM: 0 ;p (127.0.0.1, line 33)