Failed to convert socket.io event to Bacon EventStream

Below the event binding on socket.io worked correctly,

io = require('socket.io')()

io.on 'connection', (socket) ->
    console.log socket.id

io.listen 3000

Then tried to convert socket.io event to Bacon EventStream,

Bacon = require('baconjs').Bacon
io = require('socket.io')()

connections = Bacon.fromEventTarget io, 'connection'

connections.onValue (socket) ->
    console.log socket.id

io.listen 3000

Why did it fail below?

TypeError: Object connection has no method 'on'