docs: add note about ESLint --ext for .jsx files

Author: prateekbisht23

package.json

@@ -8,6 +8,7 @@
     "install:config": "cd packages/eslint-config-airbnb && npm prune && npm install",
     "install:config:base": "cd packages/eslint-config-airbnb-base && npm prune && npm install",
     "lint": "markdownlint --config linters/.markdownlint.json README.md */README.md",
+    "lint:js": "eslint -c linters/.eslintrc . --ext .js --ext .jsx",
     "pretest": "npm run --silent lint",
     "test": "npm run --silent test:config && npm run --silent test:config:base",
     "test:config": "cd packages/eslint-config-airbnb; npm test",
@@ -40,6 +41,7 @@
   },
   "homepage": "https://github.com/airbnb/javascript",
   "devDependencies": {
+    "eslint": "^8.57.1",
     "markdownlint": "^0.29.0",
     "markdownlint-cli": "^0.35.0"
   }

packages/eslint-config-airbnb-base/README.md

@@ -62,6 +62,16 @@ Our default export contains all of our ESLint rules, including ECMAScript 6+. It
 
 2. Add `"extends": "airbnb-base"` to your .eslintrc.
 
+⚠️ **Note**: ESLint only lints `.js` files by default.  
+  
+  If your project uses `.jsx` (or `.tsx` with TypeScript), you need to pass extensions to the CLI:  
+
+  ```sh
+  eslint . --ext .js,.jsx
+  ```
+
+  Without this, JSX-related rules will not apply to `.jsx` files.
+
 ### eslint-config-airbnb-base/legacy
 
 Lints ES5 and below. Requires `eslint` and `eslint-plugin-import`.

packages/eslint-config-airbnb/README.md

@@ -58,6 +58,15 @@ If you don't need React, see [eslint-config-airbnb-base](https://npmjs.com/eslin
 
 2. Add `"extends": "airbnb"` to your `.eslintrc`
 
+⚠️ **Note**: ESLint only lints `.js` files by default.  
+  If your project uses `.jsx` (or `.tsx` with TypeScript), you need to pass extensions to the CLI:  
+
+  ```sh
+  eslint . --ext .js,.jsx
+  ```
+
+  Without this, JSX-related rules will not apply to `.jsx` files.
+
 ### eslint-config-airbnb/hooks
 
 This entry point enables the linting rules for React hooks (requires v16.8+). To use, add `"extends": ["airbnb", "airbnb/hooks"]` to your `.eslintrc`.