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@hannohealth/eslint-config

A global ESLint and Prettier configuration with opinionated defaults for Hanno's JavaScript projects.

In addition to our base ESLint configuration, we also include variants for our Node, React and React Native projects.

This repository is private, but the package itself is published on npm and includes this README.

Installation

1. Install the main package:

   yarn add -D @hannohealth/eslint-config
   

2. Install the peer dependencies:

   yarn add -D @babel/core eslint prettier
   

Prettier

In your prettier.config.js file, add the following:

module.exports = require('@hannohealth/eslint-config/prettier.config');

ESLint

Base

The base configuration provides a baseline set of rules that are mainly drawn from eslint:recommended, with a few modifications.

Add the following to your .eslintrc.js file:

module.exports = {
  extends: ['@hannohealth'],
};

It introduces the following plugins:

• @babel/eslint-plugin
• eslint-plugin-jest
• eslint-plugin-jest-formatting
• eslint-plugin-import
• eslint-plugin-flowtype
• eslint-plugin-promise
• eslint-plugin-eslint-comments
• eslint-plugin-sonarjs

We also include eslint-config-prettier for Prettier compatibility and eslint-plugin-prettier to notify any Prettier errors as ESLint errors in ESLint.

Defensive programming rules

These rules are designed to enforce defensive programming, but there's still room for improvement. The following scenarios haven't been covered yet, but might be re-considered in the future:

• Enforce else clauses: https://stackoverflow.com/questions/35053371/what-is-the-benefit-of-terminating-if-else-if-constructs-with-an-else-clause/35055736#35055736. Since there doesn't seem to be a rule yet that enforces this, we may have to building a custom one in the future
• Magic numbers: avoiding them is desirable, but should be restricted to user-facing values. Right now, this would require a huge amount of changes in our repositories, so we've left it out for now: https://eslint.org/docs/rules/no-magic-numbers
• Reduce function complexity: using https://eslint.org/docs/rules/max-lines-per-function and https://github.com/SonarSource/eslint-plugin-sonarjs/blob/master/docs/rules/cognitive-complexity.md would allow us to enforce this. Right now, they have been set to a relatively high threshold, but we may reduce this over time to restrict functions to a lower number of lines. The corresponding rules are marked with TODO-complexity
• Stricter typing: Flow types can help us increase the level of type safety, but enforcing some of these stricter rules would lead to 100+ changes across our repositories, so they remain disabled for now. But we may consider reenabling them in the future. The corresponding rules are marked with TODO-typing.

Node

The node configuration extends base, but is otherwise a relatively minimal configuration which sets the environment to Node and allows us to use console logs.

To integrate, add the following to your .eslintrc.js file:

module.exports = {
  extends: ['@hannohealth/eslint-config/node'],
};

React

The react configuration extends base with some rules specific to React.

To integrate, add the following to your .eslintrc.js file:

module.exports = {
  extends: ['@hannohealth/eslint-config/react'],
};

It introduces the following plugins:

• eslint-plugin-react
• eslint-plugin-react-hooks
• eslint-plugin-cypress

React Native

The react-native configuration extends base with some rules specific to React Native. Among other things, this enables the React Native globals and allows us to properly use the module resolver in a React Native codebase.

To integrate, add the following to your .eslintrc.js file:

module.exports = {
  extends: ['@hannohealth/eslint-config/react-native'],
};

It introduces the following plugins:

• eslint-config-react-native
• eslint-config-react-native-a11y
• eslint-config-detox

Even though this configuration inherits the eslint-plugin-cypress from our React configuration, which is not suited for React Native, this shouldn't interfere with the React Native setup.

Editors

Visual Studio Code

If you're VS Code user, you may find adding this config to your .vscode/settings.json helpful when you integrate the configuration into your project. This will ensure that linting happens on save and applies the appropriate settings:

{
  "eslint.format.enable": true,
  "editor.formatOnSave": true
}

Development

To set up the project for development:

1. Clone the repository.
2. Run asdf install nodejs (assuming you are using asdf to manage your node version)
3. Run npm install --global yarn
4. Run yarn to install dependencies.

When modifying this package, we suggest the following workflow, to test the package locally, and also in a more complex project which makes more extensive use of the rules:

1. Make local changes.
2. Run yarn to update dependencies.
3. Run yarn lint:all to perform initial checks.
4. Publish the package locally with npx yalc publish.
5. Test the changes in a standalone project with npx yalc add @hannohealth/eslint-config, then yarn to install updated dependencies.
6. Push changes in this package to the new project with npx yalc publish --push, then yarn in the new project to install updated dependencies.