add eslint

.eslintrc.cjs

@@ -0,0 +1,75 @@
+/** @type {import('eslint').Linter.Config} */
+const config = {
+  root: true,
+  parser: '@typescript-eslint/parser',
+  plugins: ['@typescript-eslint', 'unicorn', 'import'],
+  extends: ['eslint:recommended'],
+  env: {
+    node: true,
+    es6: true,
+  },
+  parserOptions: {
+    ecmaVersion: 2020,
+    sourceType: 'module',
+  },
+  rules: {
+    quotes: ['error', 'single', { avoidEscape: true }],
+    camelcase: ['error', { properties: 'never' }],
+    semi: ['error', 'never'],
+    indent: [2, 2],
+    eqeqeq: ['error', 'always'],
+
+    'prefer-const': 'error',
+    'no-multiple-empty-lines': [2, { max: 1, maxEOF: 1 }],
+    'array-bracket-spacing': ['error', 'never'],
+    'brace-style': ['error', '1tbs', { allowSingleLine: true }],
+    'comma-spacing': ['error', { before: false, after: true }],
+    'no-lonely-if': 'error',
+    'dot-notation': 'error',
+    'no-else-return': 'error',
+    'no-tabs': 'error',
+    'no-trailing-spaces': [
+      'error',
+      {
+        skipBlankLines: false,
+        ignoreComments: false,
+      },
+    ],
+    'no-var': 'error',
+    'unicode-bom': ['error', 'never'],
+    curly: ['error', 'all'],
+    'object-curly-spacing': ['error', 'always'],
+    'keyword-spacing': ['error'],
+    'require-atomic-updates': 0,
+    'linebreak-style': ['error', 'unix'],
+    'unicorn/prefer-node-protocol': ['error'],
+    'import/extensions': ['error', 'ignorePackages'],
+    'no-restricted-syntax': [
+      'error',
+      'IfStatement > ExpressionStatement > AssignmentExpression',
+    ],
+    'unicorn/prefer-ternary': 'error',
+  },
+  overrides: [
+    {
+      files: ['*.ts'],
+      rules: {
+        // see https://stackoverflow.com/questions/55280555/typescript-eslint-eslint-plugin-error-route-is-defined-but-never-used-no-un
+        'no-unused-vars': 'off',
+        '@typescript-eslint/no-unused-vars': 'error',
+        '@typescript-eslint/consistent-type-imports': 'error',
+        'no-undef': 'off',
+        // allow overloads
+        'no-redeclare': 'off',
+      },
+    },
+    {
+      files: ['*.test.ts'],
+      rules: {
+        'dot-notation': 'off',
+      },
+    },
+  ],
+}
+
+module.exports = config

CONTRIBUTING.md

@@ -29,10 +29,16 @@ RUNME_PROJECT="" ./node_modules/runme/.bin/runme run clean compile
 To run the entire test pipeline, call:
 
 ```sh { name=test }
-RUNME_PROJECT="" ./node_modules/runme/.bin/runme run test:unit test:cjs
+RUNME_PROJECT="" ./node_modules/runme/.bin/runme run test:lint test:unit test:cjs
 ```
 
-This will run unit tests via Vitest:
+This will run [Eslint](https://eslint.org/) checks:
+
+```sh { name=test:lint }
+npx eslint src tests
+```
+
+unit tests via [Vitest](https://vitest.dev/):
 
 ```sh { name=test:unit }
 npx vitest --config ./vitest.config.ts