What tsconfig settings does lit recommend?

[cadamsdev]

Is the documentation on this page outdated?
https://lit.dev/docs/tools/publishing/#compiling-with-typescript

I'm looking at the lit-element-starter-ts repo and it's using slightly different settings
https://github.com/lit/lit-element-starter-ts/blob/main/tsconfig.json

Questions
For "target" is there a reason it's using "es2019"? We should be able to bump that up to at least "es2020"+ by now since it's widely supported
https://caniuse.com/?search=es2020
https://kangax.github.io/compat-table/es2016plus/

For "module" should we use "es2015" or "es2020" or does it not really matter.

For "lib" should I use "DOM.Iterable"?

[usergenic]

Apart from what we are recommending strongly in https://lit.dev/docs/tools/publishing/#compiling-with-typescript the other tsconfig concerns are mostly left up to the developer to address the specifics of their audience, pipeline, and deployment scenario etc.

AFAICT the primary reason for using newer targets is to reduce the runtime cost and bloat of inlined compilation of newer features to older analogs. Advancing the module support to es2020 from es2015 shouldn't pose an issue as far as I'm aware and I believe the recommendations on our page are meant to define a comfortable lower-bound where there is little to no syntactical "downsampling" in target compilation.

[augustjk]

To add to this:

We are making a small update to the doc site for v3 as we do plan on bumping our target to es2021. https://lit.dev/docs/v3/tools/publishing/#compiling-with-typescript

"module" doesn't matter much beyond es2015 unless you're doing dynamic imports, use import.meta or do top level awaits. https://www.typescriptlang.org/tsconfig#es2015es6es2020es2022

"DOM.Iterable" is needed if you need DOM lists like NodeList to be iterable, like to for...of or spread, etc. We do need it in our library code as we do take advantage of that, but I want to say if you don't need it yourself, it might be okay to drop it.

[justinfagnani]

I think we should probably update that section to point out which settings are basically required, which are experimentalDecorators: true, useDefineForClassFields: true, and a target of ES6 or later (to avoid needing the custom elements shim).

Nothing else is really a blocker that I know of. You could even compile to AMD or CommonJS if you're bundling to include Lit.

[cadamsdev]

Thanks everyone, very informative 🙂 that helps a lot.