vfs: fix lint errors in watch implementation

- Import setInterval/clearInterval from 'timers' module
- Use SafeSet from primordials instead of global Set
- Use object destructuring for Map iteration
- Use optional chaining for timer methods
- Use ??= operator for null coalescing assignments
- Replace @returns with @throws in abstract methods
- Fix test indentation and async IIFE patterns

Author: mcollina

lib/internal/vfs/module_hooks.js

@@ -607,9 +607,8 @@ function installHooks() {
     if (typeof options === 'function') {
       listener = options;
       options = {};
-    } else if (options == null) {
-      options = {};
     }
+    options ??= {};
 
     if (typeof filename === 'string' || filename instanceof URL) {
       const pathStr = typeof filename === 'string' ? filename : filename.pathname;
@@ -628,9 +627,8 @@ function installHooks() {
     if (typeof options === 'function') {
       listener = options;
       options = {};
-    } else if (options == null) {
-      options = {};
     }
+    options ??= {};
 
     if (typeof filename === 'string' || filename instanceof URL) {
       const pathStr = typeof filename === 'string' ? filename : filename.pathname;

lib/internal/vfs/provider.js

@@ -510,7 +510,7 @@ class VirtualProvider {
    * @param {object} [options] Watch options
    * @param {number} [options.interval] Polling interval in ms (default: 100)
    * @param {boolean} [options.recursive] Watch subdirectories (default: false)
-   * @returns {EventEmitter} A watcher that emits 'change' events
+   * @throws {ERR_METHOD_NOT_IMPLEMENTED} When not overridden by subclass
    */
   watch(path, options) {
     throw new ERR_METHOD_NOT_IMPLEMENTED('watch');
@@ -524,7 +524,7 @@ class VirtualProvider {
    * @param {number} [options.interval] Polling interval in ms (default: 100)
    * @param {boolean} [options.recursive] Watch subdirectories (default: false)
    * @param {AbortSignal} [options.signal] AbortSignal for cancellation
-   * @returns {AsyncIterable} An async iterable that yields change events
+   * @throws {ERR_METHOD_NOT_IMPLEMENTED} When not overridden by subclass
    */
   watchAsync(path, options) {
     throw new ERR_METHOD_NOT_IMPLEMENTED('watchAsync');
@@ -537,7 +537,7 @@ class VirtualProvider {
    * @param {object} [options] Watch options
    * @param {number} [options.interval] Polling interval in ms (default: 5007)
    * @param {boolean} [options.persistent] Whether the watcher should prevent exit
-   * @returns {EventEmitter} A stat watcher that emits 'change' events
+   * @throws {ERR_METHOD_NOT_IMPLEMENTED} When not overridden by subclass
    */
   watchFile(path, options) {
     throw new ERR_METHOD_NOT_IMPLEMENTED('watchFile');

lib/internal/vfs/watcher.js

@@ -5,12 +5,17 @@ const {
   Promise,
   PromiseResolve,
   SafeMap,
+  SafeSet,
   Symbol,
   SymbolAsyncIterator,
 } = primordials;
 
 const { EventEmitter } = require('events');
 const { basename, join } = require('path');
+const {
+  setInterval,
+  clearInterval,
+} = require('timers');
 
 // Private symbols
 const kVfs = Symbol('kVfs');
@@ -114,7 +119,7 @@ class VFSWatcher extends EventEmitter {
 
     // For recursive directory watching, check all tracked files
     if (this[kRecursive] && this[kTrackedFiles].size > 0) {
-      for (const [filePath, info] of this[kTrackedFiles]) {
+      for (const { 0: filePath, 1: info } of this[kTrackedFiles]) {
         const newStats = this._getStatsFor(filePath);
         if (this._statsChanged(info.stats, newStats)) {
           const eventType = this._determineEventType(info.stats, newStats);
@@ -254,9 +259,7 @@ class VFSWatcher extends EventEmitter {
    * @returns {this}
    */
   unref() {
-    if (this[kTimer] && this[kTimer].unref) {
-      this[kTimer].unref();
-    }
+    this[kTimer]?.unref?.();
     return this;
   }
 
@@ -265,9 +268,7 @@ class VFSWatcher extends EventEmitter {
    * @returns {this}
    */
   ref() {
-    if (this[kTimer] && this[kTimer].ref) {
-      this[kTimer].ref();
-    }
+    this[kTimer]?.ref?.();
     return this;
   }
 }
@@ -294,7 +295,7 @@ class VFSStatWatcher extends EventEmitter {
     this[kPersistent] = options.persistent !== false;
     this[kClosed] = false;
     this[kTimer] = null;
-    this[kListeners] = new Set();
+    this[kListeners] = new SafeSet();
 
     // Get initial stats
     this[kLastStats] = this._getStats();
@@ -434,9 +435,7 @@ class VFSStatWatcher extends EventEmitter {
    * @returns {this}
    */
   unref() {
-    if (this[kTimer] && this[kTimer].unref) {
-      this[kTimer].unref();
-    }
+    this[kTimer]?.unref?.();
     return this;
   }
 
@@ -445,9 +444,7 @@ class VFSStatWatcher extends EventEmitter {
    * @returns {this}
    */
   ref() {
-    if (this[kTimer] && this[kTimer].ref) {
-      this[kTimer].ref();
-    }
+    this[kTimer]?.ref?.();
     return this;
   }
 }

test/parallel/test-vfs-watch.js

@@ -15,9 +15,7 @@ const vfs = require('node:vfs');
   assert.strictEqual(typeof watcher.on, 'function');
   assert.strictEqual(typeof watcher.close, 'function');
 
-  let changeCount = 0;
   watcher.on('change', common.mustCall((eventType, filename) => {
-    changeCount++;
     assert.strictEqual(eventType, 'change');
     assert.strictEqual(filename, 'file.txt');
     watcher.close();
@@ -53,12 +51,15 @@ const vfs = require('node:vfs');
   const myVfs = vfs.create();
   myVfs.writeFileSync('/listener-test.txt', 'initial');
 
-  const watcher = myVfs.watch('/listener-test.txt', { interval: 50, persistent: false },
+  const watcher = myVfs.watch(
+    '/listener-test.txt',
+    { interval: 50, persistent: false },
     common.mustCall((eventType, filename) => {
       assert.strictEqual(eventType, 'change');
       assert.strictEqual(filename, 'listener-test.txt');
       watcher.close();
-    }));
+    }),
+  );
 
   setTimeout(() => {
     myVfs.writeFileSync('/listener-test.txt', 'updated');
@@ -70,15 +71,18 @@ const vfs = require('node:vfs');
   const myVfs = vfs.create();
   myVfs.writeFileSync('/watchfile.txt', 'initial');
 
-  const statWatcher = myVfs.watchFile('/watchfile.txt', { interval: 50, persistent: false },
+  const statWatcher = myVfs.watchFile(
+    '/watchfile.txt',
+    { interval: 50, persistent: false },
     common.mustCall((curr, prev) => {
       assert.ok(curr);
       assert.ok(prev);
       assert.strictEqual(curr.isFile(), true);
       // Stats should have changed
       assert.notStrictEqual(curr.mtimeMs, prev.mtimeMs);
       myVfs.unwatchFile('/watchfile.txt');
-    }));
+    }),
+  );
 
   assert.ok(statWatcher);
 
@@ -291,7 +295,7 @@ const vfs = require('node:vfs');
     }
     assert.strictEqual(eventCount, 1);
     myVfs.unmount();
-  })();
+  })().then(common.mustCall());
 }
 
 // Test VFS promises.watch directly
@@ -320,7 +324,7 @@ const vfs = require('node:vfs');
       ac.abort();
     }
     assert.strictEqual(eventCount, 1);
-  })();
+  })().then(common.mustCall());
 }
 
 // Test recursive watching