nodejs · SudhansuBandha · Mar 21, 2026 · Mar 21, 2026
diff --git a/lib/internal/watch_mode/files_watcher.js b/lib/internal/watch_mode/files_watcher.js
@@ -179,6 +179,9 @@ class FilesWatcher extends EventEmitter {
         if (ArrayIsArray(message['watch:import'])) {
           ArrayPrototypeForEach(message['watch:import'], (file) => this.filterFile(fileURLToPath(file), key));
         }
+        if (ArrayIsArray(message['watch:worker'])) {
+           ArrayPrototypeForEach(message['watch:worker'], (file) => this.filterFile(file, key));
+        }
       } catch {
         // Failed watching file. ignore
       }

diff --git a/lib/internal/worker.js b/lib/internal/worker.js
@@ -195,6 +195,17 @@ class HeapProfileHandle {
   }
 }
 
+/**
+ * Tell the watch mode that a worker file was instantiated.
+ * @param {string} filename Absolute path of the worker file
+ * @returns {void}
+ */
+function reportWorkerToWatchMode(filename) {
+  if (process.env.WATCH_REPORT_DEPENDENCIES && process.send) {
+    process.send({ 'watch:worker': [filename] });
+  }
+}
+
 class Worker extends EventEmitter {
   constructor(filename, options = kEmptyObject) {
     throwIfBuildingSnapshot('Creating workers');
@@ -275,6 +286,11 @@ class Worker extends EventEmitter {
       name = StringPrototypeTrim(options.name);
     }
 
+    // Report to watch mode if this is a regular file (not eval, internal, or data URL)
+    if (!isInternal && doEval === false) {
+      reportWorkerToWatchMode(filename);
+    }
+
     debug('instantiating Worker.', `url: ${url}`, `doEval: ${doEval}`);
     // Set up the C++ handle for the worker, as well as some internal wiring.
     this[kHandle] = new WorkerImpl(url,

diff --git a/test/parallel/test-watch-mode-worker.mjs b/test/parallel/test-watch-mode-worker.mjs
@@ -0,0 +1,67 @@
+import { describe, it } from 'node:test';
+import assert from 'node:assert';
+import { Worker } from 'node:worker_threads';
+import { tmpdir } from 'node:os';
+import { join } from 'node:path';
+import { writeFileSync, unlinkSync } from 'node:fs';
+
+describe('watch:worker event system', () => {
+  it('should report worker files to parent process', async () => {
+    const testDir = tmpdir();
+    const workerFile = join(testDir, `test-worker-${Date.now()}.js`);
+
+    try {
+      // Create a simple worker that reports itself
+      writeFileSync(workerFile, `
+        const { Worker } = require('node:worker_threads');
+        module.exports = { test: true };
+      `);
+
+      // Create a worker that requires the file
+      const worker = new Worker(workerFile);
+
+      await new Promise((resolve) => {
+        worker.on('online', () => {
+          worker.terminate();
+          resolve();
+        });
+      });
+    } finally {
+      try { unlinkSync(workerFile); } catch {}
+    }
+  });
+
+  it('should not report eval workers', (t, done) => {
+    // Eval workers should be filtered out
+    // This is a unit test that validates the condition logic
+    const isInternal = false;
+    const doEval = true;
+
+    // Condition: !isInternal && doEval === false
+    const shouldReport = !isInternal && doEval === false;
+    assert.strictEqual(shouldReport, false, 'Eval workers should not be reported');
+    done();
+  });
+
+  it('should not report internal workers', (t, done) => {
+    // Internal workers should be filtered out
+    const isInternal = true;
+    const doEval = false;
+
+    // Condition: !isInternal && doEval === false  
+    const shouldReport = !isInternal && doEval === false;
+    assert.strictEqual(shouldReport, false, 'Internal workers should not be reported');
+    done();
+  });
+
+  it('should report regular workers', (t, done) => {
+    // Regular workers should be reported
+    const isInternal = false;
+    const doEval = false;
+
+    // Condition: !isInternal && doEval === false
+    const shouldReport = !isInternal && doEval === false;
+    assert.strictEqual(shouldReport, true, 'Regular workers should be reported');
+    done();
+  });
+});