Add eslint config for typescript as a package

[kael89]

Issue #:

Will be used in https://github.com/beyondessential/tupaia-backlog/issues/256

There is also eslint-config-airbnb-typescript, which converts the Airbnb Style Guide (which uses JavaScript rules) to Typescript rules, but is not currently working with Eslint 7 and our configuration (see this issue.) It would be great to use this plugin in the near future, since currently some rules in our standard configuration (eg no-underscore-dangle) are not enabled in the config here.

Other solutions would be

• We could use both the Airbnb style guide (Javascript) and @typescript-eslint/eslint-plugin (Typescript). I tried that initially, but
  1. Most rules are duplicate and show two errors
  2. Some Airbnb rules may be redundant/need to be adjusted to a Typescript environment
• We could adjust the rules ourselves to match Airbnb, but this would re-invent eslint-config-airbnb-typescript's wheel

More information on using eslint for Typescript here: https://github.com/typescript-eslint/typescript-eslint

---

Usage

In another package's .eslintrc:

{
  "extends": "@tupaia/eslint-config-typescript"
}

No other configuration is required.

If we like this pattern, we can create @tupaia/eslint-config-base, @tupaia/eslint-config-react packages, and use them accordingly (instead of https://github.com/beyondessential/eslint-config-beyondessential ?)

[edmofro]

👍

[kael89]

Merging straight to dev as dev-related