Don't merge -- testing ESlint 9 on this branch only

.eslintrc.js

@@ -46,5 +46,39 @@ module.exports = {
         message: '`with` is disallowed in strict mode because it makes code impossible to predict and optimize.',
       },
     ],
+    // SonarJS recommended rules (same set as sonarjs.configs.recommended),
+    // explicit for legacy config (ESLint 9 defaults to flat config)
+    'sonarjs/cognitive-complexity': 'error',
+    'sonarjs/elseif-without-else': 'error',
+    'sonarjs/max-switch-cases': 'error',
+    'sonarjs/no-all-duplicated-branches': 'error',
+    'sonarjs/no-collapsible-if': 'error',
+    'sonarjs/no-collection-size-mischeck': 'error',
+    'sonarjs/no-duplicate-string': 'error',
+    'sonarjs/no-duplicated-branches': 'error',
+    'sonarjs/no-element-overwrite': 'error',
+    'sonarjs/no-empty-collection': 'error',
+    'sonarjs/no-extra-arguments': 'error',
+    'sonarjs/no-gratuitous-expressions': 'error',
+    'sonarjs/no-identical-conditions': 'error',
+    'sonarjs/no-identical-expressions': 'error',
+    'sonarjs/no-identical-functions': 'error',
+    'sonarjs/no-ignored-return': 'error',
+    'sonarjs/no-inverted-boolean-check': 'error',
+    'sonarjs/no-nested-functions': 'error',
+    'sonarjs/no-nested-switch': 'error',
+    'sonarjs/no-nested-template-literals': 'error',
+    'sonarjs/no-redundant-boolean': 'error',
+    'sonarjs/no-redundant-jump': 'error',
+    'sonarjs/no-same-line-conditional': 'error',
+    'sonarjs/no-small-switch': 'error',
+    'sonarjs/no-unused-collection': 'error',
+    'sonarjs/no-use-of-empty-return-value': 'error',
+    'sonarjs/no-useless-catch': 'error',
+    'sonarjs/non-existent-operator': 'error',
+    'sonarjs/prefer-immediate-return': 'error',
+    'sonarjs/prefer-object-literal': 'error',
+    'sonarjs/prefer-single-boolean-return': 'error',
+    'sonarjs/prefer-while': 'error',
   },
 };

README.md

@@ -30,6 +30,17 @@ npm i
 ## Linting
 This project is using StyleLint and ESLint (including the SonarJS plugin for ESLint 8).
 
+Add "eslint.useFlatConfig": false to your workspace .vscode/settings.json.
+With ESLint 9, the VS Code/Cursor ESLint extension defaults to flat config (eslint.config.js). This project still uses legacy config (.eslintrc.js), so setting eslint.useFlatConfig to false makes the extension use legacy config and the .eslintrc.js.
+
+upgrade to sonarjs 3:
+npm install eslint-plugin-sonarjs@^3.0.0 --legacy-peer-deps 2>&1
+npm install globals --legacy-peer-deps --save-dev 2>&1
+npm install ts-api-utils --legacy-peer-deps --save-dev 2>&1
+npm install --legacy-peer-deps 2>&1
+npm install @babel/core --legacy-peer-deps --save-dev 2>&1
+
+
 ```sh
 npm run lint
 ```