TypeError: io is not a function

[weeping-somnambulist]

You want to:

• report a bug
• request a feature

Current behaviour

socket.io does not work, throws obtuse error message when trying to implement. Issue is most likely in documentation, code quality (code comments are helpful here, these are useless), poor answers in issue tracker.

Basically a duplicate of #873, but that was never really answered to we get to do this all over again.

Steps to reproduce (if the current behaviour is a bug)

My code stub (I've tried all kinds of permutations of this):

const io = require('socket.io.slim.js');

var socket = io('http://localhost:9990'); // TIP: io() with no args does auto-discovery
socket.on('connect', function () {
socket.emit('ferret', 'tobi', 'woot', function (data) { console.log(data); // data will be 'tobi says woot' });
});

// error message:

2019-04-09 13:08:46.166650 [ERR] undefined:6 Exception: TypeError: io is not a function (near: "var socket = io('http://localhost:9990'); // TIP: io() with no args does auto-discovery")

Expected behaviour

It to work as shown in the example.

Setup

• OS: debian 9
• browser: chrome v8 engine
• socket.io version: commit 9c1e73c752aec63f48b511330a506d037783d897

Other information (e.g. stacktraces, related issues, suggestions how to fix)

See issue #873 for a whole bunch of other people all asking the same question.

[kapi2289]

If you downloaded this as a file, you need to add ./ before the name and you don't need to add .js extension

const io = require('./socket.io.slim');

[weeping-somnambulist]

Tried that, same behavior.

[kapi2289]

Try using this .js file in a <script> tag

<script src="/socket.io.slim.js"></script>
<script>
	var socket = io('http://localhost:9990');
</script>

OR

require('./socket.io.slim');
var socket = io('http://localhost:9990');

[weeping-somnambulist]

I am not launching this script via HTML. I've tried that exact block of code listed and got the exact same error message I gave to start with.

[kapi2289]

If you're using npm it would be better to install this lib using it

$ npm i socket.io-client

and then

const io = require("socket.io-client");

[weeping-somnambulist]

I am not using NPM. I am using the Chrome V8 engine - straight.

[kapi2289]

Is this for sure a client, not a server script? I've tried to reproduce your code, I've downloaded socket.io.slim.js from https://cdnjs.cloudflare.com/ajax/libs/socket.io/2.2.0/socket.io.slim.js and the only error I got was missing document ('cause I didn't run this in a browser)

> const io = require("./socket.io.slim");
> io("http://localhost:8888");
ReferenceError: document is not defined

[weeping-somnambulist]

It's a client, as in it is connecting to a socket as a client.

[davidwitten]

I'm running into this same issue. Were you able to find a solution @SwitchedToGitlab?

[darrachequesne]

For future readers, please see the documentation here: https://socket.io/docs/v3/client-initialization/

[adiswordfish]

Has anybody found the solution?

[mmirann]

This causes an error TypeError: io is not a function

const io = require("socket.io-client");

Solve it by using it like this:

const { io } = require("socket.io-client");

or

const io = require("socket.io-client").io;

[aliparsa]

same here by using npm -> TypeError: io is not a function