websocket - What do these numbers mean in socket.io payload?

Question

When I am using native websocket API I can see just a payload in my chrome console for sockts:

But when I use socket.io with their emit event, I can see some strange numbers before my actual payload. I do understand that colors mean that you either send or received the data, but what does the numbers like 42, 3, 2, 430, 420, 5 mean.

Is there a place I can get a full list of these numbers with descriptions?

The code which generates it is kind of big, so I just post small snippets.

Client side always look like this:

socket.emit('joinC', room, function(color){ ... });

Server side looks like this:

io.sockets.in(room).emit('moveS', {...});

Answer 1

I know you asked a while ago, but the information remains for those who are researching.

I did an analysis with reverse engineering in version 2.3.0 (socket.io) and 3.4.2 (engine.io) and got the following:

The first number is the type of communication for engine.io, using the enumerator:

Key	Value
0	"open"
1	"close"
2	"ping"
3	"pong"
4	"message"
5	"upgrade"
6	"noop"