eslint-plugin-commons

ESLint configurations used across API3 projects.

The modules consists of multiple ESLint configurations supporting wide variety of targets:

• universal - Linting rules for universal (both FE and BE) JS/TS code (with the emphasis on TS).
• react - Linting rules for React code.
• next-js - Linting rules for Next.js code.
• jest - Linting rules for Jest tests. Note, that these rules are only applied for JS/TS files with *.test.* extensions.

Getting started

1. Create an .eslintrc.js configuration file in the repo root.
2. Extend the desired configuration(s).
3. Specify the parserOptions.project option with the path to the tsconfig.json file(s).
4. Install eslint (which is a peer dependency of this module) as dev dependencies.

For example:

module.exports = {
  extends: ['plugin:@api3/eslint-plugin-commons/universal', 'plugin:@api3/eslint-plugin-commons/jest'],
  parserOptions: {
    // We focus primarily on TS and for that we need to specify the TS configs which is project specific. The following
    // is a common monorepo setup (root config and a config for each package).
    project: ['./tsconfig.json', './packages/*/tsconfig.json'],
  },
};

Linting commands

We recommend using the following linting commands inside package.json scripts:

{
  "eslint:check": "eslint --report-unused-disable-directives --cache --ext js,ts,tsx,jsx . --max-warnings 0",
  "eslint:fix": "pnpm run eslint:check --fix"
}

The --cache parameter makes ESLint create a .eslintcache file in the root of the project. This file should be put to .gitignore.

Rules

The configurations are a collection of various rulesets and the config is quite strict. In general there are rules that:

• Have a fixer (import ordering)
• Simplify code (combine two nested ifs)
• Make code more consistent (make return void pattern be split on two lines)
• Fix outdated stuff (avoid ! ts operator when not necessary)
• Avoid vulnerabilities and errors (Number.parseInt without radix)

Tip: Some rules do have fixer with multiple variants of the fixes. You need to use the IDE to prompt the fixes and choose the one you want.

Overriding rules

To override a rule, you can use the rules section key in your .eslintrc.js file. For example:

{
  rules: {
    'check-file/folder-naming-convention': 'off', // Turns of the kebab-case convention for folder names.
    'unicorn/filename-case': 'off' // Turns of the kebab-case convention for filenames.
    'import/no-default-export': 'off', // Turns off the rule that disallows default exports.
    'import/prefer-default-export': 'error' // Turns on the rule that prefers default exports.
  }
}