pol-standard

Style Guide for Frontend Development

Introduction

This repository is the home of my style guide, which includes configs for popular linting and styling tools.

It's directly inspired by the Vercel Style Guide.

The following configs are available, and are designed to be used together.

• Prettier
• ESLint
• TypeScript

Installation

All of our configs are contained in one package, pol-standard. To install:

# If you use npm
npm i --save-dev pol-standard

# If you use pnpm
pnpm i --save-dev pol-standard

# If you use Yarn
yarn add --dev pol-standard

Some of our ESLint configs require peer dependencies. We'll note those alongside the available configs in the ESLint section.

Prettier

Note: Prettier is a peer-dependency of this package, and should be installed at the root of your project.

See: https://prettier.io/docs/en/install.html

To use the shared Prettier config, set the following in package.json.

{
  "prettier": "pol-standard/prettier"
}

ESLint

Note: ESLint is a peer-dependency of this package, and should be installed at the root of your project.

See: https://eslint.org/docs/user-guide/getting-started#installation-and-usage

This ESLint config is designed to be composable.

The following base configs are available. You can use one or both of these configs, but they should always be first in extends:

• pol-standard/eslint/browser
• pol-standard/eslint/node

Note that you can scope configs, so that configs only target specific files. For more information, see: Scoped configuration with overrides.

The following additional configs are available:

• pol-standard/eslint/jest
• pol-standard/eslint/jest-react (includes rules for @testing-library/react)
• pol-standard/eslint/next (requires @next/eslint-plugin-next to be installed at the same version as next)
• pol-standard/eslint/playwright-test
• pol-standard/eslint/react
• pol-standard/eslint/typescript (requires typescript to be installed and additional configuration)
• pol-standard/eslint/vitest

You'll need to use require.resolve to provide ESLint with absolute paths, due to an issue around ESLint config resolution (see eslint/eslint#9188).

For example, use the shared ESLint config(s) in a react project, set the following in .eslintrc.js.

// Standard eslint config for next.js projects
module.exports = {
  extends: [
    require.resolve('pol-standard/eslint/browser'),
    require.resolve('pol-standard/eslint/react'),
    require.resolve('pol-standard/eslint/typescript'),
  ],
  overrides: [
    {
      files: ['**/__tests__/**/*.[jt]s?(x)', '**/?(*.)+(spec|test).[jt]s?(x)'],
      extends: [
        require.resolve('pol-standard/eslint/jest'),
        require.resolve('pol-standard/eslint/jest-react'),
        // or if you use Vitest:
        require.resolve('pol-standard/eslint/vitest'),
      ],
    },
  ],
};

Or for Next.js projects with TypeScript, set the following in .eslintrc.js.

// Standard eslint config for next.js projects
module.exports = {
  extends: [
    require.resolve('pol-standard/eslint/browser'),
    require.resolve('pol-standard/eslint/react'),
    require.resolve('pol-standard/eslint/next'),
  ],
};

Configuring ESLint for TypeScript

Some of the rules enabled in the TypeScript config require additional type information, you'll need to provide the path to your tsconfig.json.

For more information, see: https://typescript-eslint.io/docs/linting/type-linting

const { resolve } = require('node:path');

const project = resolve(__dirname, 'tsconfig.json');

module.exports = {
  root: true,
  extends: [
    require.resolve('pol-standard/eslint/node'),
    require.resolve('pol-standard/eslint/react'),
    require.resolve('pol-standard/eslint/typescript'),
    require.resolve('pol-standard/eslint/browser'),
    require.resolve('pol-standard/eslint/vitest'),
    // ... other configs
  ],
  parserOptions: {
    project,
  },
  settings: {
    'import/resolver': {
      typescript: {
        project,
      },
    },
  },
};

Configuring custom components for jsx-a11y

It's common practice for React apps to have shared components like Button, which wrap native elements. You can pass this information along to jsx-a11y via the components setting.

The below list is not exhaustive.

module.exports = {
  root: true,
  extends: [require.resolve('pol-standard/eslint/react')],
  settings: {
    'jsx-a11y': {
      components: {
        Article: 'article',
        Button: 'button',
        Image: 'img',
        Input: 'input',
        Link: 'a',
        Video: 'video',
      },
    },
  },
};

Scoped configuration with overrides

ESLint configs can be scoped to include/exclude specific paths. This ensures that rules don't "leak" into places where those rules don't apply.

In this example, Jest rules are only being applied to files matching Jest's default test match pattern.

module.exports = {
  extends: [require.resolve('pol-standard/eslint/node')],
  overrides: [
    {
      files: ['**/__tests__/**/*.[jt]s?(x)', '**/?(*.)+(spec|test).[jt]s?(x)'],
      extends: [require.resolve('pol-standard/eslint/jest')],
    },
  ],
};

A note on file extensions

By default, all TypeScript rules are scoped to files ending with .ts and .tsx.

However, when using overrides, file extensions must be included or ESLint will only include .js files.

module.exports = {
  overrides: [
    { files: [`directory/**/*.[jt]s?(x)`], rules: { 'my-rule': 'off' } },
  ],
};

TypeScript

This style guide provides multiple TypeScript configs. These configs correlate to the LTS Node.js versions, providing the appropriate lib, module, target, and moduleResolution settings for each version. The following configs are available:

Node.js Version

v16 : pol-standard/typescript/node16 v18 : pol-standard/typescript/node18 v20 : pol-standard/typescript/node20

To use the shared TypeScript config, set the following in tsconfig.json.

{
  "extends": "pol-standard/typescript/node16"
}

The base TypeScript config is also available as pol-standard/typescript which only specifies a set of general rules. You should inherit from this file when setting custom lib, module, target, and moduleResolution settings.