chore(package): upgrade to eslint v9

cspell.json

@@ -46,6 +46,7 @@
     "restream",
     "snyk",
     "streamify",
+    "tseslint",
     "typicode",
     "vhosted",
     "websockets",

eslint.config.mjs

@@ -0,0 +1,40 @@
+// @ts-check
+
+import eslint from '@eslint/js';
+import tseslint from 'typescript-eslint';
+import eslintPluginPrettierRecommended from 'eslint-plugin-prettier/recommended';
+
+export default tseslint.config(
+  // replacement of legacy `.eslintignore`
+  {
+    ignores: ['dist'],
+  },
+  // extends...
+  eslint.configs.recommended,
+  ...tseslint.configs.recommended,
+  eslintPluginPrettierRecommended,
+  {
+    files: ['*.js'],
+    rules: {
+      '@typescript-eslint/no-require-imports': 'off',
+      '@typescript-eslint/no-var-requires': 'off',
+    },
+  },
+  {
+    files: ['**/*.ts'],
+    rules: {
+      '@typescript-eslint/no-explicit-any': 'off',
+      '@typescript-eslint/no-unused-vars': [
+        'error',
+        { vars: 'all', args: 'none', ignoreRestSiblings: false },
+      ],
+      'prettier/prettier': 'warn',
+    },
+  },
+  {
+    files: ['src/**/*.ts'],
+    rules: {
+      'no-restricted-imports': ['error', { paths: ['express'] }],
+    },
+  },
+);

package.json

@@ -58,18 +58,19 @@
   "devDependencies": {
     "@commitlint/cli": "19.4.1",
     "@commitlint/config-conventional": "19.4.1",
+    "@eslint/js": "9.9.1",
     "@types/debug": "4.1.12",
+    "@types/eslint": "9.6.1",
+    "@types/eslint__js": "8.42.3",
     "@types/express": "4.17.21",
     "@types/is-glob": "4.0.4",
     "@types/jest": "29.5.12",
     "@types/micromatch": "4.0.9",
     "@types/node": "22.5.1",
     "@types/supertest": "6.0.2",
     "@types/ws": "8.5.12",
-    "@typescript-eslint/eslint-plugin": "7.16.0",
-    "@typescript-eslint/parser": "7.16.0",
     "body-parser": "1.20.2",
-    "eslint": "8.57.0",
+    "eslint": "9.9.1",
     "eslint-config-prettier": "9.1.0",
     "eslint-plugin-prettier": "5.2.1",
     "express": "4.19.2",
@@ -83,6 +84,7 @@
     "supertest": "7.0.0",
     "ts-jest": "29.2.5",
     "typescript": "5.5.4",
+    "typescript-eslint": "8.3.0",
     "ws": "8.18.0"
   },
   "dependencies": {

src/get-plugins.ts

@@ -8,9 +8,9 @@ import {
 
 export function getPlugins<TReq, TRes>(options: Options<TReq, TRes>): Plugin<TReq, TRes>[] {
   // don't load default errorResponsePlugin if user has specified their own
-  const maybeErrorResponsePlugin = !!options.on?.error ? [] : [errorResponsePlugin];
+  const maybeErrorResponsePlugin = options.on?.error ? [] : [errorResponsePlugin];
 
-  const defaultPlugins = !!options.ejectPlugins
+  const defaultPlugins = options.ejectPlugins
     ? [] // no default plugins when ejecting
     : [debugProxyErrorsPlugin, proxyEventsPlugin, loggerPlugin, ...maybeErrorResponsePlugin];
   const userPlugins: Plugin<TReq, TRes>[] = options.plugins ?? [];

src/http-proxy-middleware.ts

@@ -46,10 +46,10 @@ export class HttpProxyMiddleware<TReq, TRes> {
         debug(`proxy request to target: %O`, activeProxyOptions.target);
         this.proxy.web(req, res, activeProxyOptions);
       } catch (err) {
-        next && next(err);
+        next?.(err);
       }
     } else {
-      next && next();
+      next?.();
     }
 
     /**

src/logger.ts

@@ -1,5 +1,3 @@
-/* eslint-disable @typescript-eslint/no-empty-function */
-
 import { Logger, Options } from './types';
 
 /**

src/types.ts

@@ -3,8 +3,6 @@
  * https://github.com/DefinitelyTyped/DefinitelyTyped/blob/6f529c6c67a447190f86bfbf894d1061e41e07b7/types/http-proxy-middleware/index.d.ts
  */
 
-/* eslint-disable @typescript-eslint/no-empty-interface */
-
 import type * as http from 'http';
 import type * as httpProxy from 'http-proxy';
 import type * as net from 'net';

src/utils/function.ts

@@ -1,4 +1,4 @@
-/* eslint-disable @typescript-eslint/ban-types */
+/* eslint-disable @typescript-eslint/no-unsafe-function-type */
 
 export function getFunctionName(fn: Function): string {
   return fn.name || '[anonymous Function]';

test/types.spec.ts

@@ -1,4 +1,4 @@
-/* eslint-disable @typescript-eslint/no-empty-function */
+/* eslint-disable @typescript-eslint/no-unused-expressions */
 
 import * as express from 'express';
 import * as http from 'http';

test/unit/path-filter.spec.ts

@@ -246,7 +246,6 @@ describe('Path Filter', () => {
       });
 
       it('should not throw error with Function', () => {
-        // eslint-disable-next-line @typescript-eslint/no-empty-function
         expect(testPathFilter(() => {})).not.toThrowError(Error);
       });
     });

test/unit/path-rewriter.spec.ts

@@ -171,12 +171,10 @@ describe('Path rewriting', () => {
     });
 
     it('should not throw when function config is provided', () => {
-      // eslint-disable-next-line @typescript-eslint/no-empty-function
       expect(badFn(() => {})).not.toThrowError(Error);
     });
 
     it('should not throw when async function config is provided', () => {
-      // eslint-disable-next-line @typescript-eslint/no-empty-function
       expect(badFn(async () => {})).not.toThrowError(Error);
     });
   });

test/unit/utils/function.spec.ts

@@ -1,4 +1,3 @@
-/* eslint-disable @typescript-eslint/no-empty-function */
 import { getFunctionName } from '../../../src/utils/function';
 
 describe('getFunctionName()', () => {