On Webpack and CRA build there is an WARN "Critical dependency: the request of a dependency is an expression"

[dennisat]

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You want to:

• report a sort of bug
• request a feature

Current behaviour

When the webpack is trying to put the engine.io in a bundle, we get an optimization warning due to an expression in require() of the engine.io library.

Webpack tries to resolve required calls statically to make a minimal bundle.
Your library in node_modules/engine.io/lib/server.js file and at line 80 it doing this:

this.opts.wsEngine === "ws" ? require("ws") : require(this.opts.wsEngine);

The last require() has an expression as argument.

Can we rid of this warn?

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

• Add the engine.io into a project with a webpack builder.
• Build the app to make a bundle that has the engine.io.

Expected behaviour

• No Webpack warning: "Critical dependency: the request of a dependency is an expression"

Setup

• OS: macOs
• browser: node v12.19
• engine.io version: 4.0.1

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

The warning:

WARNING in ./node_modules/engine.io/lib/server.js 74:67-94
Critical dependency: the request of a dependency is an expression
 @ ./node_modules/engine.io/lib/engine.io.js
 @ ... the node app ...

[darrachequesne]

@dennisat do you have a suggestion on how to write this? We need to be able to load any WebSocket library that exposes an interface compatible with the ws module. (like uws or eiows)

Should we list all possible options? (but in that case they will all be included in the webpack bundle, won't they?)

[dennisat]

Yeah, I got your point.

I think the cleanest solution is to ask the reference of the ws module instead of the name (string) of it.

So we can have something like this.

const superWs = require('super-ws');
const engine = require('engine.io');

const server = new engine.Server({wsEngine: superWs});

This way will be safer for the developer since will not be possible to define a wsEngine that is not loaded in the bundle.

[darrachequesne]

That makes sense 👍 let's schedule this for v5 then.

[Navifra-Kerry]

@darrachequesne Has this problem been solved?
I have the same problem when building webpack.

[darrachequesne]

@kerry-Cho no, this is not resolved yet. Please note that this is only a warning, everything should work as expected.

[Korijn]

We're holding off on upgrading until it's fixed, since.. well.. warnings technically aren't a problem for the build or the functionality of the system, but they cause coworkers to ask questions and get worried since the error contains the words "WARN" and "Critical". :)

[Navifra-Kerry]

@darrachequesne thanks a lot , I look forward to fix that.

[darrachequesne]

Fixed by edb7343 and included in engine.io@5.0.0.