Update ESLint & Prettier to latest

[eemeli]

This should make it easier to work with the project, as atm it appears to require using npm i --legacy-peer-deps to get running.

ESLint rules that are covered by Prettier are dropped, and a "prettier" config is added to the package.json to account for the default changes in its v1 -> v2 transition.

[hybrist]

Skimmed the formatting changes, RSLGTM.

[hybrist]

Would tabs already be replaced by prettier?

[eemeli]

There are places like comments where Prettier doesn't touch tabs, while this rule would complain about them.

[eemeli]

Rebased on master to trigger CI jobs.

[ochameau]

Thanks a lot for looking into this!

Note that when running npm run prettier locally I see modifications against .waiting.html. It might relate to your very latest change.
Shouldn't we have a check against prettier on Github actions?
It looks like we only run eslint.
Would it be easy to run prettier and fail in case of modification?

This should make it easier to work with the project, as atm it appears to require using npm i --legacy-peer-deps to get running.

This is for my own culture (feel free to ignore), but for me it works without --legacy-peer-deps.

$ npm i
npm WARN eslint-plugin-prettier@3.4.1 requires a peer of eslint@>=5.0.0 but none is installed. You must install peer dependencies yourself.
npm WARN optional SKIPPING OPTIONAL DEPENDENCY: fsevents@1.2.13 (node_modules/fsevents):
npm WARN notsup SKIPPING OPTIONAL DEPENDENCY: Unsupported platform for fsevents@1.2.13: wanted {"os":"darwin","arch":"any"} (current: {"os":"linux","arch":"x64"})
removed 157 packages and audited 779 packages in 4.887s
62 packages are looking for funding
run `npm fund` for details
found 98 vulnerabilities (17 moderate, 59 high, 22 critical)
run `npm audit fix` to fix them, or `npm audit` for details
$ npm run lint
=> WORKS
$ npm run prettier
=> ALSO WORKS

As if the warning during npm i is harmless?
(I'm on npm 6.14.17 and node v14.20.1)

Otherwise I confirm that this prettier error during npm i disappear with your patch.

ESLint rules that are covered by Prettier are dropped, and a "prettier" config is added to the package.json to account for the default changes in its v1 -> v2 transition.

I tried to find what rules prettier was applying without much success. Were you able to find such list online?
Again, this isn't super important as your patch looks good as-is.

I'd be more interested in trying to align slightly more with mozilla-central linting.
Regarding prettier rules, I see the following failures:

lib/wasm.js
115:12 error Insert `,` prettier/prettier (eslint)
116:10 error Insert `,` prettier/prettier (eslint)
129:10 error Insert `,` prettier/prettier (eslint)
source-map.js
6:29 error Delete `⏎·` prettier/prettier (eslint)
8:28 error Delete `⏎·` prettier/prettier (eslint)
and many others...

Otherwise beyond prettier, there is a few rules on mozilla-central that fails:

Use the global form of 'use strict'. strict (eslint)
Parameter 'aArgs' uses Hungarian Notation, consider using 'args' instead. mozilla/no-aArgs (eslint)
use .includes instead of .indexOf mozilla/use-includes-instead-of-indexOf (eslint)
Expected { after 'if' condition. curly (eslint)
error Prefer boolean length check mozilla/prefer-boolean-length-check (eslint)

We can also look into that in followups and not necessarily align all rules.

[eemeli]

Note that when running npm run prettier locally I see modifications against .waiting.html. It might relate to your very latest change.

The .waiting.html file looks like it's been accidentally included in the repo in #335, and should be dropped. We should do that separately from this PR.

Shouldn't we have a check against prettier on Github actions? It looks like we only run eslint. Would it be easy to run prettier and fail in case of modification?

Yes, we could/should also check the Prettier styling in CI, and adding that is pretty easy. I left it out here as that'd be an additional change to the nominal version update that's done here.

This is for my own culture (feel free to ignore), but for me it works without --legacy-peer-deps.

Good point! I'll drop that here as well.

As if the warning during npm i is harmless? (I'm on npm 6.14.17 and node v14.20.1)

It looks like that goes away if you wipe out the node_modules directory first.

I tried to find what rules prettier was applying without much success. Were you able to find such list online? Again, this isn't super important as your patch looks good as-is.

That's handled by eslint-config-prettier, which disables these rules.

I'd be more interested in trying to align slightly more with mozilla-central linting.
[...]
Otherwise beyond prettier, there is a few rules on mozilla-central that fails:
[...]
We can also look into that in followups and not necessarily align all rules.

Good point. I'm going to minimise the diff of this PR by not applying the updated Prettier formatting, and file another PR applying the m-c Prettier config and a stripped-down version of the m-c ESLint config here.