Create Node-Target-Mapping.md

[orta]

This is the bare minimum to get some docs started for the node lib/target mapping.

Related:

• Typescript should support --lib node TypeScript#9466
• Target compiler flag should allow me to choose a Node.js version TypeScript#22306

[orta]

Oh, hey, it's my own PR - nice.

Yeah, this is still worth having IMO

[styfle]

@orta It might also be a good idea to also mention esnext here to avoid all downlevel-helpers.

I often use esnext with Node but I'll use es2017 for browsers.

[SimenB]

Include node 12 as well?

[BrendanBall]

Seems like this is something that should be automated with a script? There are way too many individual flags to check

[orta]

Honestly, there's a good argument for having these as options inside TypeScript itself (though it looks like that failed to stick) but I don't think this is just scriptable TBH there's not really two tables of definitions for features in node vs in TS. Just gotta do the grunt work to make sure they're in line for the docs.

[styfle]

One thing that might be difficult to get right is that Node 10 might get a new feature in Node 10.5 for example so settings target=node10 would be a moving target.

Although, there is precedent for such a flag: strict which could break an app upon updating TS when a new strict feature is introduced.

The problem is that you don't know if the user wants to target Node 10.1 or 10.5 and this would break at runtime which is much worse than strict which breaks at compile time.

Documenting is a good first step, but to add these settings into tsc will take some careful thought.

[SimenB]

Just doing whatever babel-preset-env does when people define {targets: {node: 10}} makes sense, no? Which means a moving target, but if the user don't wanna be specific, that's on the user. And precedence in babel makes it pretty ok in my mind 🙂

[AndrewKvalheim]

Link to the live page for convenience:

• Node Target Mapping

[Urigo]

If anyone wants to try the latest, not LTS version, on my personal apps I've been using latest Node (13.8.0) with native ES modules and with target es2020 and it's been working great so far.
Here is a simple example