Webpack fails silently when named import doesn't exist

[aherriot]

I'm submitting a feature request
Webpack version:
2.1.0-beta.21

Please tell us about your environment:
Linux

Current behavior:
When I try to import a named import, it fails silently if the name import does not exist. I wish webpack would fail loudly when it cannot find the import at build time

For example:

// file1.js
const var1 = 'var1'
export { var1 }

and

// file2.js
import { var2 } from './file1'
// at this point, var2 is undefined at runtime because it was never exported from file1.js

Desired behavior:
Instead, I want it to fail at build time. Is there a webpack option or some other technique I can use to catch this error sooner?

• What is the motivation / use case for changing the behavior?
  This will catch typos at build time, and prevent a lot of headaches caused by undefined imports.
• Browser: [all ]
• Language: [ES6/7]

[TheLarkInn]

Would you mind updating to webpack 2.1.0-beta.25 and confirm this is an issue or not still?

[aherriot]

This issue still persists with webpack2.1.0-beta.25 and if I remember correctly it also existed in webpack 1, though I didn't test it.

[sokra]

Babel configuration?

[aherriot]

This issue is not specific to only files that use the babel loader. I am thinking that I can write a custom loader to check for this, but it would be nice if webpack checked for undefined imports by default, or at least through an option.

[Jessidhia]

The issue is with webpack 2's harmony imports handler.

I can see, in the code, that there is some code to deal with that case, but it doesn't seem to get invoked in cases like in the sample.

The only thing helping in those cases is eslint-plugin-imports.

[SpaceK33z]

@Kovensky do you know if this issue is still relevant? And if not, could you close it?

[aherriot]

Simple webpack examples seem to work, but I have a complex project at work that has this problem still. I am not sure what the difference is.

[SpaceK33z]

@aherriot is that with the latest 2.2.0 version?

[adrianhelvik]

The behaviour is still the same. This is a really useful feature in native ES2015 modules and in the most recent version of create-react-app. Is there a way to enable it? Including it as a default would definitely warrant a major version bump, but in my opinion it is the right choice to do asap considering that's the way the native implementation works.

[sokra]

There is a warning for this case now

[aherriot]

@sokra What version was this fixed in?

[pascalpp]

@aherriot did you ever figure this out in your project? I'm trying to migrate a large CommonJS codebase to wepback3 and ES modules, can't figure out how to get these warnings.

[pascalpp]

I simplified my entry point and my config a lot, and figured out that the warning is generated by webpack if I disable babel-loader. With babel-loader enabled for .js files, the warnings are suppressed or swallowed somehow. I'm currently searching the babel-loader repo for answers on that.

Update: specifically the issue appears to be with babel-preset-env which transpiles ES6 modules and doesn't appear to warn about missing imports. I set my .babelrc to disable module transpilation in babel, and let webpack do that for me. Like so:

{
  "presets": [
      ["env", {
          "modules": false
      }],
      "react"
  ]
}

[adrienharnay]

Bumping into this as well, babel-preset-env's modules: false doesn't fix it in my case.

#6339

[matthieu-foucault]

Having the same issue with webpack 3.11.0 and babel 6.26

[Vasikaran]

@matthieu-foucault This issue were fixed in latest webpack and not documented yet. You can use strictExportPresence options in module configuration which throws an error when imported modules doesn't exist in the exported file. But it took a huge time even I'm running webpack in development mode.

[matthieu-foucault]

Thanks for the info! I decided to go the long way around and use Typescript to fix this issue (among other things that were becoming hard to maintain given the size of our project) 🙂

[harrywhite4]

strictExportPresence works great and is documented now https://webpack.js.org/configuration/module/#module-contexts

[fatso83]

@harrywhite4 strictExportPresence is deprecated and the docs do not mention what is replacing it for this use case. We had some failing builds, and it took a long while for us to to notice the warning about a missing member in an import.

[sokra]

It's not deprecated. Seems like this sneaked into the wrong docs section. Maybe you can send a PR to the docs to fix it.