feat: usage of ES6 class syntax

[theoludwig]

What is the purpose of this pull request? (put an "X" next to item)

[ ] Documentation update
[ ] Bug fix
[x] New feature
[ ] Other, please explain:

What changes did you make? (Give an overview)

• Convert var into let/const in README
• Update parseOpts references in tests and README to the new resolveEslintConfig function introduced in Add more JSDoc annotations + validate them and refactor to make them clearer #248
• Convert the Linter function constructor to ES6 class syntax
• Better respect the JavaScript camelCase/PascalCase notation, by exporting the Linter class as PascalCase instead of camelCase

Before:

const { linter } = require('standard-engine')

After:

const { Linter } = require('standard-engine')

Which issue (if any) does this pull request address?

Fixes #250

Is there anything you'd like reviewers to focus on?

BREAKING CHANGES introduced by this PR:

• Export is now called Linter, not linter
• Calling Linter() instead of new Linter() doesn't work anymore.

[voxpelli]

Overall 👍 Some minor thoughts, but nothing major.

I like the size of this PR, will be possible to wrap up and merge quite quickly.

Breaking changes introduced by this PR:

• Export is now called Linter, not linter
• It may be that calling Linter() instead of new Linter() doesn't work anymore.

[voxpelli]

This casing change isn't strictly caused by ES6, but I do like it and it should be done eventually.

I would prefer this export:

Suggested change

	module.exports.cli = require('./bin/cmd')
	module.exports.Linter = Linter
	module.exports = {
	cli: require('./bin/cmd'),
	Linter
	};

[theoludwig]

Changed the export but without the semicolon, that's why I didn't commit your suggestion. 😄

EDIT: It is not working with the StandardCliOptions type inside bin/cmd.js.

Error extracted from the test failing in the GitHub Actions:
Error: bin/cmd.js(8,29): error TS2694: Namespace '"/home/runner/work/standard-engine/standard-engine/index".export=' has no exported member 'Linter'.

So it's probably better to do the exports like that:

module.exports.cli = require('./bin/cmd')
module.exports.Linter = Linter

[theoludwig]

Could you review again my PRs (this one and #252) when you have some time? @voxpelli
Thank you very much for your help! 😄

[LinusU]

Neat 👍

[voxpelli]

Excellent! Very good improvement

[voxpelli]

The intention with doing require('../') here rather than in the top of the file must have been to avoid loading it if another linter had been provided, but then the code would have to be:

Suggested change

	const { Linter } = require('../')
	const standard = rawOpts.linter || new Linter(opts)
	const standard = rawOpts.linter || new ( require('../').Linter)(opts)

Just an observation 🤔

[theoludwig]

Somehow, if I put const { Linter } = require('../') at the top of the file, the tests are failing :
TypeError: Linter is not a constructor.
Do you have an idea, why?
Maybe you can test it yourself locally (I'm using Node.js v16.9.1).

But, yes if I take your recommendation const standard = rawOpts.linter || new (require('../').Linter)(opts), it is working, I'll change it then. 👍

[voxpelli]

I like the move to the bottom and the lowercasing of it!