fs: use default w flag for writeFileSync with utf8 encoding

PR-URL: #50990
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Yagiz Nizipli <yagiz.nizipli@sentry.io>

lib/fs.js

@@ -2341,6 +2341,8 @@ function writeFileSync(path, data, options) {
 
   validateBoolean(flush, 'options.flush');
 
+  const flag = options.flag || 'w';
+
   // C++ fast path for string data and UTF8 encoding
   if (typeof data === 'string' && (options.encoding === 'utf8' || options.encoding === 'utf-8')) {
     if (!isInt32(path)) {
@@ -2349,7 +2351,7 @@ function writeFileSync(path, data, options) {
 
     return binding.writeFileUtf8(
       path, data,
-      stringToFlags(options.flag),
+      stringToFlags(flag),
       parseFileMode(options.mode, 'mode', 0o666),
     );
   }
@@ -2359,8 +2361,6 @@ function writeFileSync(path, data, options) {
     data = Buffer.from(data, options.encoding || 'utf8');
   }
 
-  const flag = options.flag || 'w';
-
   const isUserFd = isFd(path); // File descriptor ownership
   const fd = isUserFd ? path : fs.openSync(path, flag, options.mode);
 

test/parallel/test-fs-write-file-sync.js

@@ -101,6 +101,22 @@ tmpdir.refresh();
   assert.strictEqual(content, 'hello world!');
 }
 
+// Test writeFileSync with no flags
+{
+  const utf8Data = 'hello world!';
+  for (const test of [
+    { data: utf8Data },
+    { data: utf8Data, options: { encoding: 'utf8' } },
+    { data: Buffer.from(utf8Data, 'utf8').toString('hex'), options: { encoding: 'hex' } },
+  ]) {
+    const file = tmpdir.resolve(`testWriteFileSyncNewFile_${Math.random()}.txt`);
+    fs.writeFileSync(file, test.data, test.options);
+
+    const content = fs.readFileSync(file, { encoding: 'utf-8' });
+    assert.strictEqual(content, utf8Data);
+  }
+}
+
 // Test writeFileSync with an invalid input
 {
   const file = tmpdir.resolve('testWriteFileSyncInvalid.txt');