Add eslint and JavaScript linting in GitHub Actions

[eason9487]

Changes proposed in this Pull Request:

Implements parts of #4

• Add eslint, related deps and their configurations.
• Add a GitHub Actions workflow to run JavaScript linting.
• Fix all linting errors and warnings.

Before merging this PR:

• Wait for Add annotation actions of eslint and stylelint for annotating the linting results via their formatter #35 to be released.
• Change actions-v1-pre to actions-v1.

Detailed test instructions:

1. npm install
2. npm run lint:js locally to test the eslint
   • 💡 It may gets some import/no-unresolved warnings because the node_modules directories in sub-packages don't exist. Those warnings will disappear after running npm install in those sub-packages.
3. View the check that was intentionally left with linting errors and warnings.
4. View the annotations attached to this PR:
   
5. View the Check tab of this PR to see the successful linting check.

[puntope]

💅 Maybe running this WorkFlow on PR against trunk would be enough?

[eason9487]

If the linting check only runs on PR against trunk, PR to PR, like this current one (#34), wouldn't be run. I think finding out linting errors earlier should be ideal.

[puntope]

What I meant is to remove the push directive.

[eason9487]

The temporarily merged code of a PR to be run checks is not always the same as the merged one after a PR actually gets merged.

For example, if there are other commits are pushed to trunk after this PR was opened, this PR won't be triggered and run the check again if there are no conflicts. When two PR change the same file like this:

const config = {
+	hello: '123', // Added by PR A
	howdy: '000',
+	hello: '456', // Added by PR B
 };
};

Both PR could pass the check, but it would be a problem after merging. When this happens, the check run on push events of trunk might find out this problem.

[puntope]

Right! Thanks for the explanation 👌

[puntope]

💅 If we are going to set up a global package.json I'd also add a .nvmrc file

[eason9487]

Added in fa4b346.

[puntope]

❓

When I run npm run lint:js I got this error:

[eason9487]

@puntope, thanks for the review.

When I run npm run lint:js I got this error: [...]

Thanks for catching this. Seems it results in a different node_modules structure in the initial install, and somehow the flatted structure of package-lock after running npm dedupe conflicts with npm install. I added the "prettier": "npm:[email protected]" by 6489389 to make it stable.

Could you help with another round of code reviews?

[puntope]

✅ LGTM

• Tested lint:js locally. I checked forcing some errors.
• Checked the action check
• Checked the code quality