breaking: drop node v10/v13/v15 support

[aladdin-add]

The version of ESLint you are using.
n/w

The problem you want to solve.
just like previous major releases, we can drop node v10 support in eslint v8.

• node v10 EOL: 2021-04-30
• node v13 EOL: 2020-06-01

Your take on the correct solution to problem.
drop node v10, v13 support.

question: do we like some features introduced in node v12, so we can pick a version( e.g. ">=12.8.0")?

Are you willing to submit a pull request to implement this change?
y

[nzakas]

TSC Summary: Node.JS 10 is EOL at the end of April and Node.JS 13 EOL is the end of June.

TSC Question: How do we want to handle these? Should we plan on a major release to coincide with one or both?

[ljharb]

Just because it’s EOL doesn’t mean there needs to be any rush to drop support for it.

if you’re doing a major anyways, then that’s a fine time to drop support if there’s a benefit to doing so.

[btmills]

We have several small changes waiting for the next major release, so we'll start working toward a v8 release and discuss this and other changes in the v8 project at the next TSC meeting.

[btmills]

This is now accepted as part of ESLint v8.0.0.

[nzakas]

Note: We want to use import() for flat config, so we probably want to ensure whatever minimum version we decide on supports that.

[mysticatea]

ES modules have gotten stable in ^12.22.0 || ^14.17.0 || >=15.3.0.

• v12.22.0 mark modules implementation as stable
• v14.17.0 mark modules implementation as stable
• v15.3.0 mark modules implementation as stable

Also, we can use class fields as well, except together with optional chaining (obj.#foo is OK, but obj?.#foo isn't).
We still cannot use private methods.

[btmills]

Thanks for looking at that, @mysticatea. In addition to those class features, there are a few other features we'll be able to start using:

• Object.fromEntries().
• Array.prototype.flat() and flatMap(). There's already a todo comment for this in Chore: Remove lodash #14287.
• String.prototype.matchAll().
• Separators in numeric literals.

Those are all supported by every version where ESM is stable.

• For Node 12, 12.22.0 is the most recent semver-minor release as of writing.
• For Node 14, 14.17.0 is the most recent release as of writing.
• For Node 15, I didn't see anything after 15.3.0 that we'd be able to use. There are some improvements to promise-based APIs and workers that have been backported to 14 but not 12, so we couldn't use them.
• For Node 16, there are syntax features after 16.0.0, but we wouldn't be able to use them because they haven't been backported.

I recommend we adopt @mysticatea's version range proposed above: ^12.22.0 || ^14.17.0 || >=15.3.0.

[ljharb]

(private methods and accessors only work in node v14.6+, unfortunately)

[nzakas]

Per #14592 (comment), we are also dropping support for v15.x, which is EOL this month.