chore: upgrade to eslint 9.x

Upgrades to eslint 9.x and simplifies the customisation of our config.

bench/memory/sax-parser.js

@@ -4,6 +4,8 @@ import memwatch from '@airbnb/node-memwatch';
 import { SAXParser } from '../../packages/parse5-sax-parser/dist/index.js';
 import { finished } from 'parse5-test-utils/dist/common.js';
 
+/* eslint-disable no-console */
+
 const heapDiffMeasurement = new memwatch.HeapDiff();
 
 let maxMemUsage = 0;

bench/perf/index.js

@@ -7,6 +7,8 @@ import * as parse5 from '../../packages/parse5/dist/index.js';
 import { ParserStream as parse5Stream } from '../../packages/parse5-parser-stream/dist/index.js';
 import * as parse5Upstream from 'parse5';
 
+/* eslint-disable no-console */
+
 const hugePagePath = new URL('../../test/data/huge-page/huge-page.html', import.meta.url);
 const treeConstructionPath = new URL('../../test/data/html5lib-tests/tree-construction', import.meta.url);
 const saxPath = new URL('../../test/data/sax/', import.meta.url);

eslint.config.js

@@ -0,0 +1,69 @@
+import eslintjs from '@eslint/js';
+import eslintConfigPrettier from 'eslint-config-prettier';
+import { configs as tseslintConfigs } from 'typescript-eslint';
+import globals from 'globals';
+
+const { configs: eslintConfigs } = eslintjs;
+
+const sourceFiles = ['bench/**/*.js', 'scripts/**/*.ts', 'packages/*/lib/**/*.ts'];
+const testFiles = ['test/**/*.{ts,js}'];
+const ignoreFiles = [
+    'test/data/html5lib-tests',
+    'test/data/html5lib-tests-fork',
+    'packages/*/dist/',
+    'test/dist/',
+    'docs/build/',
+];
+const allFiles = [...sourceFiles, ...testFiles];
+
+export default [
+    {
+        files: allFiles,
+    },
+    {
+        ignores: ignoreFiles,
+    },
+    {
+        languageOptions: {
+            globals: {
+                ...globals.nodeBuiltin,
+                ...globals.es2019,
+            },
+        },
+    },
+    eslintConfigs.recommended,
+    ...tseslintConfigs.recommended,
+    {
+        rules: {
+            'no-console': 'error',
+            curly: ['error', 'all'],
+            'prefer-arrow-callback': 'error',
+            'one-var': ['error', 'never'],
+            'no-var': 'error',
+            'prefer-const': 'error',
+            'object-shorthand': 'error',
+            'prefer-destructuring': [
+                'error',
+                {
+                    object: true,
+                    array: false,
+                },
+            ],
+            'prefer-template': 'error',
+            'arrow-body-style': ['error', 'as-needed'],
+        },
+    },
+    {
+        files: ['**/*.ts'],
+        rules: {
+            '@typescript-eslint/no-unsafe-declaration-merging': 'off',
+            '@typescript-eslint/no-non-null-assertion': 'warn',
+            '@typescript-eslint/no-explicit-any': 'warn',
+            '@typescript-eslint/explicit-function-return-type': 'error',
+            '@typescript-eslint/consistent-type-imports': 'error',
+
+            '@typescript-eslint/no-unused-vars': ['error', { argsIgnorePattern: '^_' }],
+        },
+    },
+    eslintConfigPrettier,
+];