Convert source code into TypeScript

[g-plane]

Should we consider converting the source code of this project into TypeScript? We can leverage type checking with TypeScript. Also, .d.ts files can be generated for downstream users when compiling.

It may take long time to do this coversion, so we can enable allowJs and start progressive conversion.

[kaicataldo]

I'm generally 👎 for this proposal, particularly since we're not using TypeScript in ESLint core.

Relevant PR: eslint/eslint#12082

[nzakas]

I agree with @kaicataldo. I’d like ESLint to remain pure JavaScript to enable us to best test ESLint on itself.

[g-plane]

Hey, this is espree, not ESLint.

[nzakas]

Espree is part of the ESLint project.

[simonbuchan]

Note that webpack is using typescript in --checkJs to get at least some typechecking without needing a build step. Not sure if that matters to you.

[nzakas]

We aren't going to move forward with this, so closing.