worker: add ref/unref to web workers

doc/api/globals.md

@@ -1401,6 +1401,11 @@ Inside a worker, \[`worker_threads.parentPort`]\[] is the port behind
 `self.postMessage()` and the worker's `message` events, `isMainThread` is
 `false`, and `workerData` is `undefined`.
 
+Because that thread keeps the event loop alive, `Worker` instances also get
+the non-standard `ref()` and `unref()` methods of [`node:worker_threads`][]
+{Worker}: `worker.unref()` allows the program to exit even while the worker
+is still running, and `worker.ref()` restores the default behavior.
+
 As a rule of thumb, use [`node:worker_threads`][] directly when a program
 needs `workerData`, a custom `env` or `execArgv`, resource limits, stdio
 redirection, the `'online'` and `'exit'` events, or `worker.threadId`;

lib/internal/webworker.js

@@ -865,11 +865,24 @@ class Worker extends EventTarget {
     // arguments, and returned the same return value."
     this[kWorker]?.postMessage(message, transfer);
   }
+
+  // The following properties are non-standard, Node.js extensions
+  ref() {
+    validateThisInternalField(this, kWorker, 'Worker');
+    this[kWorker]?.ref();
+  }
+
+  unref() {
+    validateThisInternalField(this, kWorker, 'Worker');
+    this[kWorker]?.unref();
+  }
 }
 
 ObjectDefineProperties(Worker.prototype, {
   terminate: kEnumerableProperty,
   postMessage: kEnumerableProperty,
+  ref: kEnumerableProperty,
+  unref: kEnumerableProperty,
   [SymbolToStringTag]: {
     __proto__: null,
     configurable: true,

test/fixtures/web-worker/echo.js

@@ -0,0 +1,5 @@
+'use strict';
+
+addEventListener('message', (event) => {
+  postMessage(event.data);
+});

test/parallel/test-webworker-ref-unref.js

@@ -0,0 +1,34 @@
+// Flags: --experimental-web-worker
+'use strict';
+
+const common = require('../common');
+const fixtures = require('../common/fixtures');
+const assert = require('assert');
+
+for (const method of ['ref', 'unref']) {
+  assert.throws(() => Worker.prototype[method].call({}),
+                { code: 'ERR_INVALID_THIS' });
+}
+
+{
+  // Both are no-ops on a worker whose script could not be loaded.
+  const worker = new Worker(fixtures.fileURL('web-worker', 'nonexistent.js').href);
+  worker.addEventListener('error', common.mustCall());
+  worker.unref();
+  worker.ref();
+}
+
+const worker = new Worker(fixtures.fileURL('web-worker', 'echo.js').href);
+
+worker.addEventListener('error', common.mustNotCall('worker failed'));
+worker.addEventListener('message', common.mustCall(({ data }) => {
+  assert.strictEqual(data, 'hello');
+  worker.terminate();
+}));
+
+process.once('beforeExit', common.mustCall(() => {
+  worker.ref();
+  worker.postMessage('hello');
+}));
+
+worker.unref();