Update to eslint v9

eslint.config.js

@@ -0,0 +1,58 @@
+import astroEslintParser from 'astro-eslint-parser';
+import eslintPluginAstro from 'eslint-plugin-astro';
+import globals from 'globals';
+import js from '@eslint/js';
+import tseslint from 'typescript-eslint';
+import typescriptParser from '@typescript-eslint/parser';
+
+export default [
+  js.configs.recommended,
+  ...eslintPluginAstro.configs['flat/recommended'],
+  ...tseslint.configs.recommended,
+  {
+    languageOptions: {
+      globals: {
+        ...globals.browser,
+      },
+    },
+  },
+  {
+    files: ['**/*.astro'],
+    languageOptions: {
+      parser: astroEslintParser,
+      parserOptions: {
+        parser: '@typescript-eslint/parser',
+        extraFileExtensions: ['.astro'],
+      },
+    },
+  },
+  {
+    files: ['**/*.{js,jsx,astro}'],
+    rules: {
+      'no-mixed-spaces-and-tabs': ['error', 'smart-tabs'],
+    },
+  },
+  {
+    // Define the configuration for `<script>` tag.
+    // Script in `<script>` is assigned a virtual file name with the `.js` extension.
+    files: ['**/*.{ts,tsx}', '**/*.astro/*.js'],
+    languageOptions: {
+      parser: typescriptParser,
+    },
+    rules: {
+      // Note: you must disable the base rule as it can report incorrect errors
+      'no-unused-vars': 'off',
+      '@typescript-eslint/no-unused-vars': [
+        'error',
+        {
+          argsIgnorePattern: '^_',
+          destructuredArrayIgnorePattern: '^_',
+        },
+      ],
+      '@typescript-eslint/no-non-null-assertion': 'off',
+    },
+  },
+  {
+    ignores: ['dist', 'node_modules', '.github', 'types.generated.d.ts'],
+  },
+];