Add 'require' flag to preload JS modules

[ooflorent]

This PR contains a:

• bugfix
• new feature
• code refactor
• test update
• typo fix
• metadata update

Motivation / Use-Case

Add --require flag (and its alias -r) to preload JS modules. The flag could be added multiple times to load multiple modules.

webpack-serve -r dotenv/env

Breaking Changes

none

Additional Info

The biggest wins with this flag is the possibility to use dotenv and esm packages. Unfortunately, esm does nothing because cosmiconfig uses require-from-string (track progress here cosmiconfig/cosmiconfig#109).

[codecov]

Codecov Report

Merging #83 into master will decrease coverage by 12.2%.
The diff coverage is 100%.

@@             Coverage Diff             @@
##           master      #83       +/-   ##
===========================================
- Coverage    92.7%   80.49%   -12.21%     
===========================================
  Files           7        7               
  Lines         274      282        +8     
===========================================
- Hits          254      227       -27     
- Misses         20       55       +35

Impacted Files	Coverage Δ
cli.js	97.43% <100%> (+0.66%)	⬆️
lib/bus.js	58.82% <0%> (-41.18%)	⬇️
lib/config.js	65.38% <0%> (-34.62%)	⬇️
lib/options.js	73.56% <0%> (-16.1%)	⬇️
lib/server.js	83.07% <0%> (-4.62%)	⬇️
index.js	91.48% <0%> (-4.26%)	⬇️

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[shellscape]

this will be a win for folks 🎉 thanks for putting it together

we'll need package-lock.json removed from the commit - that's something we maintain during publish because it's messy

and we'll need a test or two added to cli.js to make sure this doesn't break unexpectedly in the future.

[shellscape]

why this change? pretty sure that fails linting due to the prefer-destructuring rule.

[ooflorent]

Because it is using ES6 features for nothing. It is a clever trick but does not improve readability and may be confusing for JS beginners. I've reverted this change.

[shellscape]

@ooflorent I wonder if we could mock require-from-string and intercept the requiring of that module with https://www.npmjs.com/package/mock-require.

What I'm thinking is that we mock that module before requiring cosmiconfig, if the --require flag is used. They're passing the content of the file as well as the file path of the found config file. We could then use that path to require the file so the hooks can do their thing. That's the theory anyhow. Thoughts?

[ooflorent]

That could work but it's hacky. Another option is to replace cosmiconfig by something else.

[shellscape]

cosmiconfig really is the best at what it does. I'm not overly opposed to hacks for a development module when that hack is for somewhat-edge cases.

[ooflorent]

@shellscape If you PR something, I'll be glad to review it ;)