scaffolding for typescript

[cellog]

This PR sets up the project to use typescript. It does not yet change any of the actual functionality.

It adds:

1. @babel/typescript for compiling typescript to js using babel
2. @typescript-eslint and needed sub-packages for linting typescript
3. disables no-unused-vars in favor of @typescript-eslint/no-unused-vars, and adds a new strict rule exception - any variable whose name starts with '_' can be ignored as unused
4. tsconfig.json which controls the type validation one will see in VSCode, and the result of explicitly running tsc
5. a new check-types script that is added to prepare to check types prior to compilation

Once this is merged, the actual work of typescript conversion may commence

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[timdorr]

Looks like eslint-plugin-import got dropped from the lockfile somehow. Try another npm install and that should fix the CI failure.

[JustFly1984]

Guys we are using tsdx to build our library at @react-google-maps/api and it prove to be reliable and produces very small bundle

[markerikson]

@JustFly1984 : I've looked at tsdx a bit, and agree it seems cool. That said, we've got an existing build setup, and I'd think it'll be easier to integrate TS into what we've got now (especially given our use of Babel) then it would be to switch build setups entirely.

[JustFly1984]

Btw you don't need eslint-plugin-import for typescript, more than that - it just doesn't support TS

[markerikson]

I just created a new ts-conversion branch and updated the PR to merge into that instead, so we can play around there without disturbing master.

[cellog]

Btw you don't need eslint-plugin-import for typescript, more than that - it just doesn't support TS

The PR addresses this issue. If eslint-plugin-import is removed, the build fails. It is part of the react-app preset. In .eslintrc, we disable it with:

    'no-unused-vars': 'off',

and then replace it with the typescript version here:

    '@typescript-eslint/no-unused-vars': [
      'error',
      {
        vars: 'all',
        args: 'after-used',
        ignoreRestSiblings: true,
        argsIgnorePattern: '^_' // ignore unused variables whose name is '_'
      }
    ]

I spent many long hours in a past project trying to figure this out :). If you have a better solution, let's make it happen!

[cellog]

ah - I did not look at .travis.yml, I'll fix the linting errors in examples and push that later, then this should be good to go

[cellog]

OK, so feedback needed here - the todos-flow example flips out because it is in flow, and not ts. Do we need to lint this example? If so, we will need to add some special case linting that excludes .ts and does flow linting.

For now, I'm adding it to .eslintignore so we can make progress.

[timdorr]

I'm happy with just getting rid of that example. I really don't see it adding much value to Redux. It's for Flow users, not Redux users.

[JustFly1984]

Well, actually you don’t need create-React-app preset either, you can use eslint-plugin-React, eslint-plugin-React-hooks, eslint-plugin-React-perf and that will be enough.