Bump eslint to 9.x

.npmignore

@@ -32,6 +32,7 @@ jest.setup.js
 # eslint
 .eslintrc
 .eslintignore
+eslint.config.mjs
 
 # lib
 lib

eslint.config.mjs

@@ -0,0 +1,62 @@
+import globals from 'globals';
+import babelParser from '@babel/eslint-parser';
+import typescriptPlugin from '@typescript-eslint/eslint-plugin';
+import tsParser from '@typescript-eslint/parser';
+import path from 'node:path';
+import { fileURLToPath } from 'node:url';
+import js from '@eslint/js';
+import { FlatCompat } from '@eslint/eslintrc';
+import jest from 'eslint-plugin-jest';
+
+const __filename = fileURLToPath(import.meta.url);
+const __dirname = path.dirname(__filename);
+const compat = new FlatCompat({
+    baseDirectory: __dirname,
+    recommendedConfig: js.configs.recommended,
+    allConfig: js.configs.all
+});
+
+export default [{
+    ignores: ['**/dist', '**/node_modules'],
+}, {
+    files: ['spec/**'],
+    ...jest.configs['flat/recommended'],
+    rules: {
+        ...jest.configs['flat/recommended'].rules,
+        'jest/prefer-expect-assertions': 'off',
+    },
+}, ...compat.extends('eslint:recommended'), {
+    languageOptions: {
+        globals: {
+            ...globals.node
+        },
+        parser: babelParser,
+    },
+    rules: {
+        'no-console': 'off',
+        'no-invalid-this': 'warn',
+        'no-undef': 'error',
+        'no-unused-vars': 'warn',
+        'no-var': ['error'],
+        quotes: ['error', 'single'],
+        strict: [2, 'never'],
+    },
+}, ...compat.extends(
+    'eslint:recommended',
+    'plugin:@typescript-eslint/eslint-recommended',
+    'plugin:@typescript-eslint/recommended',
+).map(config => ({
+    ...config,
+    files: ['src/**/*.d.ts'],
+})), {
+    files: ['src/**/*.d.ts'],
+    plugins: {
+        '@typescript-eslint': typescriptPlugin,
+    },
+    rules: {
+        '@typescript-eslint/no-explicit-any': 'off',
+    },
+    languageOptions: {
+        parser: tsParser,
+    },
+}];

jest.config.js

@@ -1,3 +1,4 @@
+/* eslint-disable quotes */
 /**
  * For a detailed explanation regarding each configuration property, visit:
  * https://jestjs.io/docs/configuration