Update to ESLint 9, support flat config, and require Node.js 18 (#175)

Co-authored-by: Sindre Sorhus <sindresorhus@gmail.com>

Author: prantlf

.github/workflows/main.yml

@@ -10,12 +10,11 @@ jobs:
       fail-fast: false
       matrix:
         node-version:
-          - 16
-          - 14
-          - 12
+          - 20
+          - 18
     steps:
-      - uses: actions/checkout@v2
-      - uses: actions/setup-node@v2
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
         with:
           node-version: ${{ matrix.node-version }}
       - run: npm install

conf/eslint.js

@@ -0,0 +1,8 @@
+module.exports = [
+	{
+		rules: {
+			'no-alert': 1,
+			'camelcase': 2
+		}
+	}
+];

conf/eslint.json

@@ -1,10 +1,12 @@
 'use strict';
-module.exports = function (context) {
-	return {
-		CallExpression(node) {
-			if (node.callee.name === 'alert') {
-				context.report(node, 'testing custom rules.');
+module.exports = {
+	create(context) {
+		return {
+			CallExpression(node) {
+				if (node.callee.name === 'alert') {
+					context.report(node, 'testing custom rules.');
+				}
 			}
-		}
-	};
+		};
+	}
 };

conf/rules/no-alert.js

@@ -1,10 +1,15 @@
 'use strict';
+
+const noAlertRule = require('./conf/rules/no-alert');
+
 module.exports = grunt => {
 	grunt.initConfig({
 		eslint: {
 			options: {
-				overrideConfigFile: 'conf/eslint.json',
-				rulePaths: ['conf/rules'],
+				overrideConfigFile: 'conf/eslint.js',
+				plugins: {
+					noAlertRule
+				},
 				quiet: true
 			},
 			validate: ['test/fixture/{1,2}.js']

gruntfile.js

@@ -11,7 +11,7 @@
 		"url": "https://sindresorhus.com"
 	},
 	"engines": {
-		"node": ">=12"
+		"node": "^18.18.0 || ^20.9.0 || >=21.1.0"
 	},
 	"scripts": {
 		"test": "grunt"
@@ -28,10 +28,10 @@
 	],
 	"dependencies": {
 		"chalk": "^4.1.2",
-		"eslint": "^8.44.0"
+		"eslint": "^9.0.0"
 	},
 	"devDependencies": {
-		"grunt": "^1.0.1",
+		"grunt": "^1.6.1",
 		"grunt-cli": "^1.4.3",
 		"grunt-shell": "^4.0.0"
 	},

package.json

@@ -29,11 +29,15 @@ grunt.registerTask('default', ['eslint']);
 ### Custom config and rules
 
 ```js
+const noAlertRule = require('./conf/rules/no-alert');
+
 grunt.initConfig({
 	eslint: {
 		options: {
-			overrideConfigFile: 'conf/eslint.json',
-			rulePaths: ['conf/rules']
+			overrideConfigFile: 'conf/eslint.js',
+			plugins: {
+				noAlertRule
+			}
 		},
 		target: ['file.js']
 	}
@@ -46,7 +50,7 @@ grunt.initConfig({
 grunt.initConfig({
 	eslint: {
 		options: {
-			format: require('eslint-tap')
+			format: './node_modules/eslint-tap/index.js'
 		},
 		target: ['file.js']
 	}