.eslintrc.js

module.exports = {
	extends: [
		"airbnb-base",
		"airbnb-typescript/base",
		"plugin:jest/recommended",
		"plugin:jest/style",
		"plugin:@typescript-eslint/recommended",
		"plugin:import/typescript",
		"prettier",
	],

	parserOptions: { tsconfigRootDir: __dirname, project: "./tsconfig.eslint.json" },

	env: { es2021: true, node: true, "jest/globals": true },

	plugins: ["jest"],

	ignorePatterns: [
		"node_modules",
		"dist",
		"coverage",
		// "**/*.d.ts",
		"!.*.js",
		"!.*.cjs",
		"!.*.mjs",
	],

	rules: {
		// enforce curly brace usage
		curly: ["error", "all"],

		// allow class methods which do not use this
		"class-methods-use-this": "off",

		// Allow use of ForOfStatement - no-restricted-syntax does not allow us to turn off a rule. This block overrides the airbnb rule entirely
		// https://github.com/airbnb/javascript/blob/7152396219e290426a03e47837e53af6bcd36bbe/packages/eslint-config-airbnb-base/rules/style.js#L257-L263
		"no-restricted-syntax": [
			"error",
			{
				selector: "ForInStatement",
				message:
					"for..in loops iterate over the entire prototype chain, which is virtually never what you want. Use Object.{keys,values,entries}, and iterate over the resulting array.",
			},
			{
				selector: "LabeledStatement",
				message:
					"Labels are a form of GOTO; using them makes code confusing and hard to maintain and understand.",
			},
			{
				selector: "WithStatement",
				message:
					"`with` is disallowed in strict mode because it makes code impossible to predict and optimize.",
			},
		],

		// underscore dangle will be handled by @typescript-eslint/naming-convention
		"no-underscore-dangle": "off",

		// enforce consistent sort order
		"sort-imports": ["error", { ignoreCase: true, ignoreDeclarationSort: true }],

		// enforce convention in import order
		"import/order": [
			"error",
			{
				"newlines-between": "never",
				groups: ["builtin", "external", "internal", "parent", "sibling", "index"],
				alphabetize: { order: "asc", caseInsensitive: true },
			},
		],

		// ensure consistent array typings
		"@typescript-eslint/array-type": "error",

		// ban ts-comment except with description
		"@typescript-eslint/ban-ts-comment": [
			"error",
			{
				"ts-expect-error": "allow-with-description",
				"ts-ignore": "allow-with-description",
				"ts-nocheck": true,
				"ts-check": false,
			},
		],

		// prefer type imports and exports
		"@typescript-eslint/consistent-type-exports": [
			"error",
			{ fixMixedExportsWithInlineTypeSpecifier: true },
		],
		"@typescript-eslint/consistent-type-imports": ["error", { prefer: "type-imports" }],

		// enforce consistent order of class members
		"@typescript-eslint/member-ordering": "error",

		// set up naming convention rules
		"@typescript-eslint/naming-convention": [
			"error",
			// camelCase for everything not otherwise indicated
			{ selector: "default", format: ["camelCase"] },
			// allow known default exclusions
			{
				selector: "default",
				filter: { regex: "^(_id|__v)$", match: true },
				format: null,
			},
			// allow variables to be camelCase or UPPER_CASE
			{ selector: "variable", format: ["camelCase", "UPPER_CASE"] },
			// allow known variable exclusions
			{
				selector: "variable",
				filter: { regex: "^(_id|__v)$", match: true },
				format: null,
			},
			{
				// variables ending in Service should be PascalCase
				selector: "variable",
				filter: { regex: "^.*Service$", match: true },
				format: ["PascalCase"],
			},
			// do not enforce format on property names
			{ selector: "property", format: null },
			// PascalCase for classes and TypeScript keywords
			{
				selector: ["typeLike"],
				format: ["PascalCase"],
			},
		],

		// disallow parameter properties in favor of explicit class declarations
		"@typescript-eslint/no-parameter-properties": "error",

		// ensure unused variables are treated as an error
		// overrides @typescript-eslint/recommended -- '@typescript-eslint/no-unused-vars': 'warn'
		// https://github.com/typescript-eslint/typescript-eslint/blob/main/packages/eslint-plugin/src/configs/recommended.ts
		"@typescript-eslint/no-unused-vars": "warn",
	},

	overrides: [
		{
			files: ["**/*.ts"],
			extends: ["plugin:@typescript-eslint/recommended-requiring-type-checking"],
			rules: {
				// disable rules turned on by @typescript-eslint/recommended-requiring-type-checking which are too noisy
				// https://github.com/typescript-eslint/typescript-eslint/blob/main/packages/eslint-plugin/src/configs/recommended-requiring-type-checking.ts
				"@typescript-eslint/no-unsafe-argument": "off",
				"@typescript-eslint/no-unsafe-assignment": "off",
				"@typescript-eslint/no-unsafe-call": "off",
				"@typescript-eslint/no-unsafe-member-access": "off",
				"@typescript-eslint/no-unsafe-return": "off",
				"@typescript-eslint/restrict-template-expressions": "off",
				"@typescript-eslint/unbound-method": "off",

				// force explicit member accessibility modifiers
				"@typescript-eslint/explicit-member-accessibility": ["error", { accessibility: "no-public" }],

				// enforce return types on module boundaries
				"@typescript-eslint/explicit-module-boundary-types": "error",

				// allow empty functions
				"@typescript-eslint/no-empty-function": "off",
			},
		},

		{
			files: ["**/index.ts"],
			rules: {
				// prefer named exports for certain file types
				"import/prefer-default-export": "off",
				"import/no-default-export": "error",
			},
		},

		{
			files: [
				"**/test/**/*.[jt]s?(x)",
				"**/__tests__/**/*.[jt]s?(x)",
				"**/?(*.)+(spec|test).[jt]s?(x)",
			],
			rules: {
				// allow tests to create multiple classes
				"max-classes-per-file": "off",

				// allow side effect constructors
				"no-new": "off",

				// allow import with CommonJS export
				"import/no-import-module-exports": "off",

				// allow dev dependencies
				"import/no-extraneous-dependencies": [
					"error",
					{ devDependencies: true, optionalDependencies: false, peerDependencies: false },
				],

				// disallow use of "it" for test blocks
				"jest/consistent-test-it": ["error", { fn: "test", withinDescribe: "test" }],

				// ensure all tests contain an assertion
				"jest/expect-expect": "error",

				// no commented out tests
				"jest/no-commented-out-tests": "error",

				// no duplicate test hooks
				"jest/no-duplicate-hooks": "error",

				// valid titles
				"jest/valid-title": "error",

				// no if conditionals in tests
				"jest/no-if": "error",

				// expect statements in test blocks
				"jest/no-standalone-expect": "error",

				// disallow returning from test
				"jest/no-test-return-statement": "error",

				// disallow truthy and falsy in tests
				"jest/no-restricted-matchers": ["error", { toBeFalsy: null, toBeTruthy: null }],

				// prefer called with
				"jest/prefer-called-with": "error",

				"jest/no-conditional-expect": "off"
			},
		},

		{
			files: [
				"**/test/**/*.ts?(x)",
				"**/__tests__/**/*.ts?(x)",
				"**/?(*.)+(spec|test).ts?(x)",
			],
			rules: {
				// allow explicit any in tests
				"@typescript-eslint/no-explicit-any": "off",

				// allow non-null-assertions
				"@typescript-eslint/no-non-null-assertion": "off",

				// allow empty arrow functions
				"@typescript-eslint/no-empty-function": ["warn", { allow: ["arrowFunctions"] }],
			},
		},

		{
			files: ["./.*.js", "./*.js"],
			rules: {
				// allow requires in config files
				"@typescript-eslint/no-var-requires": "off",
			},
		},

		{
			files: ["**/*.d.ts"],
			rules: {
				// allow tests to create multiple classes
				"max-classes-per-file": "off",
				"@typescript-eslint/naming-convention": "off",

				"lines-between-class-members": "off",
				"@typescript-eslint/lines-between-class-members": "off",
				"@typescript-eslint/member-ordering": "off",
				"@typescript-eslint/ban-types": "off"
			},
		},
	],
};