[Proposal] Add type definitions via d.ts files around public API surface

Things I’ve reviewed

• Read the types.md
• Read through some previous issues
• Read through some PRs such as https://github.com/open-wc/open-wc/pull/277

Preamble

In my opinion, the current required setup to get type hinting is way too cumbersome. Perhaps less so for Javascript, for sure; however, having to go as far as changing my build process to get type hinting only for this project’s packages is kind of a no-go. I’m not going to propose changing this project to Typescript—that’s kind of a separate matter, but I do believe getting a more frictionless experience with types is needed.

Proposal

I’d like to propose exposing type definition files (*.d.ts) that cover the public API surface of this project. This is similar to what DefinitelyTyped does, but without having to install a separate package. As an example, several of sindresorhus’s repos follow this pattern.

Benefit

• Types work out-of-the-box without having to convert the entire source of the project.
• Can be done gradually and without impacting current source.
• // @ts-ignore comments in Javascript code would no longer be required.
• Only needs to cover public API.

Downsides

• Types could fall out of sync because not tied to the source, but on the bright side, this only applied to the public API.

[daKmoR]

soooo @runem made a fantastic script that might get us exactly where we want to be… until tsc supports it directly 💪

see it here… pls help verify if the output is what you would expect/need https://github.com/open-wc/open-wc/pull/678

[daKmoR]

types for testing has been implemented in https://github.com/open-wc/open-wc/pull/697