optional dependencies when using es6 import/export

[RaananW]

I am trying to define optional externals in an es6 project.
The feature exists - #339 , but there is no flag that I can set in the (externals) configuration to make a dependency optional. Digging into the code I found that optional is a flag checking for reasons, and if every reason's dependency is marked as optional. But I can't seem to find where it is defined.

What would be the best way to define an external dependency optional? Have I missed something and it is possible doing it using configuration?

[sokra]

try {
  require("external");
} catch(e) {
  // fallback
}

[RaananW]

Thanks

But 😄
to keep an es6 (or esm) project consistent, I don't want to use require when importing anything. I use the import keyword.
As a fallback, we are also offering a UMD module, built with webpack. The UMD definition has the option to automatically define the require as optional, but, as i wrote, it is not a flag anywhere I can find.
You can see it here - https://github.com/webpack/webpack/blob/master/lib/UmdMainTemplatePlugin.js#L162
and here for AMD externals as global - https://github.com/webpack/webpack/blob/master/lib/UmdMainTemplatePlugin.js#L97

All I actually want to know is how to get the (external) module to be defined as optional, without using the try-catch method.

[webpack-bot]

This issue had no activity for at least half a year.

It's subject to automatic issue closing if there is no activity in the next 15 days.

[alexander-akait]

Answer above #7713 (comment)

[RaananW]

I know closing the ticket is automated, but this ticket is not resolved.
The issue is the fact that this has to be done manually, so es6 projects can't use this feature. Unless there is something I'm missing, of course.
The feature is already there, there is just a need to expose it using configuration.

[lorisleiva]

Hi everyone 👋

I've read a few issues across GitHub of libraries using optional externals via a try/catch. None of them are fully resolved.

The major issue is that you get a warning Module not found: Error: Can't resolve 'xxx'.

If a library wants to offer optional adapters for third-party dependencies out-of-the-box, its users will receive a warning for each optional dependencies that this user doesn't need. I'm not sure that this is an acceptable behaviour.

To be more precise.

Current context: wrap require('xxx') in a try/catch and register xxx as an external in webpack configurations.
Current behaviour: library users get WARNING Module not found: Error: Can't resolve 'xxx'
Expected behaviour: no warning

Am I missing something?

Here's a couple of those issues I was talking about:

• Resolve iconv-lite warning wowserhq/blizzardry#101
• [WIP] IntegratesQueryBuilder mixin lorisleiva/javel#3 (comment)

[ozyman42]

@lorisleiva here's another example: websockets/ws#1220
What would recommend in this case and what is the best fix? I dislike the idea that I need to know about every transitive dependency which has optional dependencies and I need to go explicitly externalize them in the webpack config. While this could lead to a can of worms implementation, it would be nice if webpack could analyze the code to see if the require is within a try catch, then auto externalize if so.

[slorber]

Hey,

If there is a good solution to this problem, please let me know.

In the meantime, you can probably disable the warning with warningsFilter option: https://webpack.js.org/configuration/stats/#statswarningsfilter

        stats: {
          warningsFilter: [
            (warning) =>
              warning.includes("Can't resolve 'xyz"),
          ],
        },

Not sure it will work for you because our setup is not very usual (we actually duplicate some code from Webpack), but this worked for me.

Edit, for Webpack 5 I believe this has changed a bit and now it became:

        ignoreWarnings: [
          (e) => e.message.includes("Can't resolve 'xyz'"),
        ],