chore: add prettier config for consistent formatting

.prettierignore

@@ -0,0 +1,10 @@
+# ignore github workflow files
+.github/workflows/*
+
+# ignore markdown files
+README.md
+NOTICE.md
+
+# ignore package json files
+package.json
+package-lock.json

.prettierrc

@@ -0,0 +1,9 @@
+{
+    "trailingComma": "all",
+    "tabWidth": 4,
+    "semi": true,
+    "singleQuote": true,
+    "bracketSpacing": false,
+    "arrowParens": "always",
+    "singleAttributePerLine": true
+}

eslint.config.js

@@ -1,3 +1,4 @@
+import eslintPluginPrettierRecommended from 'eslint-plugin-prettier/recommended';
 import {defineConfig} from 'eslint/config';
 import indexConfig from './index.js';
 
@@ -6,11 +7,16 @@ import indexConfig from './index.js';
  */
 const config = defineConfig([
     indexConfig,
+    eslintPluginPrettierRecommended,
     {
         rules: {
-            'import/extensions': ['error', 'ignorePackages', {
-                js: 'always',
-            }],
+            'import/extensions': [
+                'error',
+                'ignorePackages',
+                {
+                    js: 'always',
+                },
+            ],
             'rulesdir/prefer-import-module-contents': 'off',
         },
     },

package.json

@@ -9,7 +9,7 @@
   },
   "scripts": {
     "test": "NODE_OPTIONS=--experimental-vm-modules jest",
-    "lint": "eslint ."
+    "lint": "eslint . && prettier --check ."
   },
   "type": "module",
   "dependencies": {
@@ -53,6 +53,9 @@
   "homepage": "https://github.com/Expensify/eslint-config-expensify#readme",
   "devDependencies": {
     "@typescript-eslint/rule-tester": "^8.44.1",
-    "jest": "^29.7.0"
+    "eslint-config-prettier": "^10.1.8",
+    "eslint-plugin-prettier": "^5.5.4",
+    "jest": "^29.7.0",
+    "prettier": "^3.6.2"
   }
 }