io.on is not a function

Question

I have this code working for receiving data from my Arduino but I will like to send data back to my Arduino and get a response on my client page. I added a listening functi

Answer 1

Your value of io is not what it should be.

The usual way of doing things is like this:

var app = require('http').createServer(handler)
var io = require('socket.io')(app);
var fs = require('fs');

app.listen(80);

io.on('connect', ...);

But I'm guessing that your value of io is something like this:

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

That's not the same thing. That's the module handle. But, when you do it this way:

var io = require('socket.io')(app);

Then, io is a socket.io instance. You can bind listeners to an instance, not to the module handle.

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In every single socket.io server-side example on this doc page, they use one of these forms:

var io = require('socket.io')(app);
var io = require('socket.io')(port);
var io = require('socket.io')(server);

with this:

 io.on('connection', ....);

Nowhere do they do:

var io = require('socket.io`);
io.listen(server);
io.on('connection', ....);

That's just the wrong value for io.

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Long story, shortened, you need to fix what you assign to io to be consistent with the docs. It's the return value from require('socket.io')(app); that gives you a socket.io instance object that you can then set up event handlers on.