adding linting for typescript

[bdomen-ggl]

Adding GTS as a linter for typescript.
GTS wraps eslint, eslint for react, and prettier and comes with default (yet overridable) configurations.
This is to support the React/Typescript UI work in cross-media-measurement.

[wfa-reviewable]

This change is 

[bdomen-ggl]

Where should I setup GTS? I think this is the wrong spot despite cpplint installation is right above. setup-linters seems better, but everything is handled in the index file. I could just add this as another step in setup-linters if it makes sense to move it there.

[SanjayVas]

Reviewed 2 of 2 files at r1, all commit messages.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @bdomen-ggl)

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lint/action.yml line 53 at r1 (raw file):

Previously, bdomen-ggl wrote…

Where should I setup GTS? I think this is the wrong spot despite cpplint installation is right above. setup-linters seems better, but everything is handled in the index file. I could just add this as another step in setup-linters if it makes sense to move it there.

The way it's split currently is that setup-linters is for setting up linters that are downloaded/installed manually. Those that are installed using a package manager are installed here, so this is the right place.

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lint/action.yml line 55 at r1 (raw file):

    - name: Install gts
      shell: bash
      run: npm install --save-dev gts eslint eslint-config-react-app prettier

Can you explain why we use this flag? Apologies, I don't know npm that well.

Code quote:

--save-dev

[bdomen-ggl]

Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @SanjayVas)

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lint/action.yml line 55 at r1 (raw file):

Previously, SanjayVas (Sanjay Vasandani) wrote…

Can you explain why we use this flag? Apologies, I don't know npm that well.

Super specifically, --save-dev will install packages to a dev-dependency section. These dependencies will not be installed when someone else installs your package like npm install MyPackage. If you clone the repo and run npm install it will install all packages (both dependencies and dev dependencies).

--save-dev is for dependencies that are strictly for the developers of the package, usually for things like test frameworks, bundling, linting, etc. Without the dependency the app will still work fine.

For example, things like react and react-router are necessary for an app to work (react as the UI framework and react-router to navigate pages within the SPA). jest would be a dev dependency since it isn't used by the app. This helps npm by not installing packages that an end user wouldn't need.

In this particular case, there's not really an "app" in the traditional sense, so it doesn't really matter if we have it as dev dependencies or regular dependencies. I left it out of habit since linting is generally installed in this way.