ESLint configurations used at American Express.

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📖 Table of Contents

• Usage
• Contributing
• License
• Code of Conduct

🤹‍ Usage

This config is compatible with ESLint >= 9.

Installation

npm install --save-dev eslint@^9.0.0 @eslint/compat@^2.0.0 eslint-config-amex

If using Jest for unit tests and browser tests

npm install --save-dev typescript eslint-plugin-jest@^29.0.0 eslint-plugin-jest-dom@^5.0.0

Configuration

Create a eslint.config.js file (or eslint.config.mjs if your package.json does not have "type": "module"). This Flat Config file is the new configuration format as of eslint@9. See https://eslint.org/docs/v9.x/use/configure/configuration-files for more details.

JavaScript

If working in JavaScript, your eslint.config.js should be:

import { fileURLToPath } from 'node:url';
import { defineConfig } from 'eslint/config';
import { includeIgnoreFile } from '@eslint/compat';
import amexJsConfig from 'eslint-config-amex';
import amexJsTestConfig from 'eslint-config-amex/test-config';
import amexBrowserTestConfig from 'eslint-config-amex/browser-test-config';
import amexIgnorePrettierRulesConfig from 'eslint-config-amex/ignore-prettier-rules-config';

const gitignorePath = fileURLToPath(new URL('.gitignore', import.meta.url));

export default defineConfig([
  includeIgnoreFile(gitignorePath),
  amexJsConfig(),
  amexJsTestConfig(),
  amexBrowserTestConfig(),
  amexIgnorePrettierRulesConfig(), // include if using Prettier in your project
]);

TypeScript

If working in TypeScript, your eslint.config.js should be:

import { fileURLToPath } from 'node:url';
import { defineConfig } from 'eslint/config';
import { includeIgnoreFile } from '@eslint/compat';
import amexTsConfig from 'eslint-config-amex/ts-config';
import amexTsTestConfig from 'eslint-config-amex/ts-test-config';
import amexBrowserTestConfig from 'eslint-config-amex/browser-test-config';
import amexIgnorePrettierRulesConfig from 'eslint-config-amex/ignore-prettier-rules-config';

const gitignorePath = fileURLToPath(new URL('.gitignore', import.meta.url));

export default defineConfig([
  includeIgnoreFile(gitignorePath),
  amexTsConfig(),
  amexTsTestConfig(),
  amexBrowserTestConfig(),
  amexIgnorePrettierRulesConfig(), // include if using Prettier in your project
]);

Overrides

Each of the config functions can be customized by supplying an object with the files, ignores, and rules properties, as defined in the ESLint docs. The files and ignores properties will completely override the default values for those configs, whereas the rules property will be merged with the existing rules for that config. For convenience, JS_FILES and JS_AND_TS_FILES constants are exported from eslint-config-amex/constants.

import amexJsConfig from 'eslint-config-amex';
import amexJsTestConfig from 'eslint-config-amex/test-config';
import { JS_FILES } from 'eslint-config-amex/constants';

export default defineConfig([
  // other configs
  amexJsConfig({
    ignores: [`**/src/ignore-directory/**/${JS_FILES}`],
  })
  amexJsTestConfig({
    files: [`**/custom-test-directory/**/${JS_FILES}`],
    rules: {
      'jest/no-large-snapshots': ['error', { maxSize: 100 }],
    }
  })
]);

For reference, these are the default files for each config.

Config	Default Files Applied To
eslint-config-amex	**/*.{js,jsx,mjs,cjs,snap}
eslint-config-amex/test-config	**/__{tests,mocks}__/**/*.{js,jsx,mjs,cjs,snap}
eslint-config-amex/ts-config	**/*.{js,jsx,mjs,cjs,ts,tsx,mts,cts,snap}
eslint-config-amex/ts-test-config	**/__{tests,mocks}__/**/*.{js,jsx,mjs,cjs,ts,tsx,mts,cts,snap}
eslint-config-amex/browser-test-config	**/__tests__/{browser,a11y}/**/*.{js,jsx,mjs,cjs,ts,tsx,mts,cts,snap}
eslint-config-amex/ignore-prettier-rules-config	**/*.{js,jsx,mjs,cjs,ts,tsx,mts,cts,snap}

Linting vs Formatting

	Linting	Formatting
Purpose	Used to improve code quality and catch bugs	Used to format and stylize code
Recommended Tool	ESLint	Prettier

Previously, formatting was done as part of linting by using eslint-plugin-prettier. However, this is no longer recommended.

If you want formatting in your repo, install Prettier and use the eslint-config-amex/ignore-prettier-rules-config config (see above) in order to disable any ESLint rules which may conflict with Prettier.

🏆 Contributing

We welcome Your interest in the American Express Open Source Community on Github. Any Contributor to any Open Source Project managed by the American Express Open Source Community must accept and sign an Agreement indicating agreement to the terms below. Except for the rights granted in this Agreement to American Express and to recipients of software distributed by American Express, You reserve all right, title, and interest, if any, in and to Your Contributions. Please fill out the Agreement.

Please feel free to open pull requests and see CONTRIBUTING.md to learn how to get started contributing.

🗝️ License

Any contributions made under this project will be governed by the Apache License 2.0.

🗣️ Code of Conduct

This project adheres to the American Express Community Guidelines. By participating, you are expected to honor these guidelines.