worker: add ESM version examples to worker docs

PR-URL: https://github.com/nodejs/node/pull/57645
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

doc/api/worker_threads.md

@@ -9,7 +9,13 @@
 The `node:worker_threads` module enables the use of threads that execute
 JavaScript in parallel. To access it:
 
-```js
+```mjs
+import worker from 'node:worker_threads';
+```
+
+```cjs
+'use strict';
+
 const worker = require('node:worker_threads');
 ```
 
@@ -21,9 +27,43 @@ Unlike `child_process` or `cluster`, `worker_threads` can share memory. They do
 so by transferring `ArrayBuffer` instances or sharing `SharedArrayBuffer`
 instances.
 
-```js
+```mjs
+import {
+  Worker,
+  isMainThread,
+  parentPort,
+  workerData,
+} from 'node:worker_threads';
+
+if (!isMainThread) {
+  const { parse } = await import('some-js-parsing-library');
+  const script = workerData;
+  parentPort.postMessage(parse(script));
+}
+
+export default function parseJSAsync(script) {
+  return new Promise((resolve, reject) => {
+    const worker = new Worker(new URL(import.meta.url), {
+      workerData: script,
+    });
+    worker.on('message', resolve);
+    worker.on('error', reject);
+    worker.on('exit', (code) => {
+      if (code !== 0)
+        reject(new Error(`Worker stopped with exit code ${code}`));
+    });
+  });
+};
+```
+
+```cjs
+'use strict';
+
 const {
-  Worker, isMainThread, parentPort, workerData,
+  Worker,
+  isMainThread,
+  parentPort,
+  workerData,
 } = require('node:worker_threads');
 
 if (isMainThread) {
@@ -84,7 +124,25 @@ of data passed to the spawning thread's `worker.setEnvironmentData()`.
 Every new `Worker` receives its own copy of the environment data
 automatically.
 
-```js
+```mjs
+import {
+  Worker,
+  isMainThread,
+  setEnvironmentData,
+  getEnvironmentData,
+} from 'node:worker_threads';
+
+if (isMainThread) {
+  setEnvironmentData('Hello', 'World!');
+  const worker = new Worker(new URL(import.meta.url));
+} else {
+  console.log(getEnvironmentData('Hello'));  // Prints 'World!'.
+}
+```
+
+```cjs
+'use strict';
+
 const {
   Worker,
   isMainThread,
@@ -116,12 +174,6 @@ Is `true` if this code is running inside of an internal [`Worker`][] thread (e.g
 node --experimental-loader ./loader.js main.js
 ```
 
-```cjs
-// loader.js
-const { isInternalThread } = require('node:worker_threads');
-console.log(isInternalThread);  // true
-```
-
 ```mjs
 // loader.js
 import { isInternalThread } from 'node:worker_threads';
@@ -129,14 +181,24 @@ console.log(isInternalThread);  // true
 ```
 
 ```cjs
-// main.js
+// loader.js
+'use strict';
+
 const { isInternalThread } = require('node:worker_threads');
+console.log(isInternalThread);  // true
+```
+
+```mjs
+// main.js
+import { isInternalThread } from 'node:worker_threads';
 console.log(isInternalThread);  // false
 ```
 
-```mjs
+```cjs
 // main.js
-import { isInternalThread } from 'node:worker_threads';
+'use strict';
+
+const { isInternalThread } = require('node:worker_threads');
 console.log(isInternalThread);  // false
 ```
 
@@ -150,7 +212,21 @@ added: v10.5.0
 
 Is `true` if this code is not running inside of a [`Worker`][] thread.
 
-```js
+```mjs
+import { Worker, isMainThread } from 'node:worker_threads';
+
+if (isMainThread) {
+  // This re-loads the current file inside a Worker instance.
+  new Worker(new URL(import.meta.url));
+} else {
+  console.log('Inside Worker!');
+  console.log(isMainThread);  // Prints 'false'.
+}
+```
+
+```cjs
+'use strict';
+
 const { Worker, isMainThread } = require('node:worker_threads');
 
 if (isMainThread) {
@@ -183,7 +259,35 @@ For example, Node.js marks the `ArrayBuffer`s it uses for its
 
 This operation cannot be undone.
 
-```js
+```mjs
+import { MessageChannel, markAsUntransferable } from 'node:worker_threads';
+
+const pooledBuffer = new ArrayBuffer(8);
+const typedArray1 = new Uint8Array(pooledBuffer);
+const typedArray2 = new Float64Array(pooledBuffer);
+
+markAsUntransferable(pooledBuffer);
+
+const { port1 } = new MessageChannel();
+try {
+  // This will throw an error, because pooledBuffer is not transferable.
+  port1.postMessage(typedArray1, [ typedArray1.buffer ]);
+} catch (error) {
+  // error.name === 'DataCloneError'
+}
+
+// The following line prints the contents of typedArray1 -- it still owns
+// its memory and has not been transferred. Without
+// `markAsUntransferable()`, this would print an empty Uint8Array and the
+// postMessage call would have succeeded.
+// typedArray2 is intact as well.
+console.log(typedArray1);
+console.log(typedArray2);
+```
+
+```cjs
+'use strict';
+
 const { MessageChannel, markAsUntransferable } = require('node:worker_threads');
 
 const pooledBuffer = new ArrayBuffer(8);
@@ -223,7 +327,18 @@ added: v21.0.0
 Check if an object is marked as not transferable with
 [`markAsUntransferable()`][].
 
-```js
+```mjs
+import { markAsUntransferable, isMarkedAsUntransferable } from 'node:worker_threads';
+
+const pooledBuffer = new ArrayBuffer(8);
+markAsUntransferable(pooledBuffer);
+
+isMarkedAsUntransferable(pooledBuffer);  // Returns true.
+```
+
+```cjs
+'use strict';
+
 const { markAsUntransferable, isMarkedAsUntransferable } = require('node:worker_threads');
 
 const pooledBuffer = new ArrayBuffer(8);
@@ -252,7 +367,23 @@ This has no effect on `ArrayBuffer`, or any `Buffer` like objects.
 
 This operation cannot be undone.
 
-```js
+```mjs
+import { markAsUncloneable } from 'node:worker_threads';
+
+const anyObject = { foo: 'bar' };
+markAsUncloneable(anyObject);
+const { port1 } = new MessageChannel();
+try {
+  // This will throw an error, because anyObject is not cloneable.
+  port1.postMessage(anyObject);
+} catch (error) {
+  // error.name === 'DataCloneError'
+}
+```
+
+```cjs
+'use strict';
+
 const { markAsUncloneable } = require('node:worker_threads');
 
 const anyObject = { foo: 'bar' };
@@ -309,7 +440,26 @@ using `worker.on('message')`, and messages sent from the parent thread
 using `worker.postMessage()` are available in this thread using
 `parentPort.on('message')`.
 
-```js
+```mjs
+import { Worker, isMainThread, parentPort } from 'node:worker_threads';
+
+if (isMainThread) {
+  const worker = new Worker(new URL(import.meta.url));
+  worker.once('message', (message) => {
+    console.log(message);  // Prints 'Hello, world!'.
+  });
+  worker.postMessage('Hello, world!');
+} else {
+  // When a message from the parent thread is received, send it back:
+  parentPort.once('message', (message) => {
+    parentPort.postMessage(message);
+  });
+}
+```
+
+```cjs
+'use strict';
+
 const { Worker, isMainThread, parentPort } = require('node:worker_threads');
 
 if (isMainThread) {
@@ -365,7 +515,6 @@ The example below shows the use of of `postMessageToThread`: it creates 10 neste
 the last one will try to communicate with the main thread.
 
 ```mjs
-import { fileURLToPath } from 'node:url';
 import process from 'node:process';
 import {
   postMessageToThread,
@@ -378,7 +527,7 @@ const channel = new BroadcastChannel('sync');
 const level = workerData?.level ?? 0;
 
 if (level < 10) {
-  const worker = new Worker(fileURLToPath(import.meta.url), {
+  const worker = new Worker(new URL(import.meta.url), {
     workerData: { level: level + 1 },
   });
 }
@@ -402,6 +551,9 @@ channel.onmessage = channel.close;
 ```
 
 ```cjs
+'use strict';
+
+const process = require('node:process');
 const {
   postMessageToThread,
   threadId,
@@ -455,7 +607,20 @@ Receive a single message from a given `MessagePort`. If no message is available,
 that contains the message payload, corresponding to the oldest message in the
 `MessagePort`'s queue.
 
-```js
+```mjs
+import { MessageChannel, receiveMessageOnPort } from 'node:worker_threads';
+const { port1, port2 } = new MessageChannel();
+port1.postMessage({ hello: 'world' });
+
+console.log(receiveMessageOnPort(port2));
+// Prints: { message: { hello: 'world' } }
+console.log(receiveMessageOnPort(port2));
+// Prints: undefined
+```
+
+```cjs
+'use strict';
+
 const { MessageChannel, receiveMessageOnPort } = require('node:worker_threads');
 const { port1, port2 } = new MessageChannel();
 port1.postMessage({ hello: 'world' });
@@ -501,7 +666,18 @@ A special value that can be passed as the `env` option of the [`Worker`][]
 constructor, to indicate that the current thread and the Worker thread should
 share read and write access to the same set of environment variables.
 
-```js
+```mjs
+import process from 'node:process';
+import { Worker, SHARE_ENV } from 'node:worker_threads';
+new Worker('process.env.SET_IN_WORKER = "foo"', { eval: true, env: SHARE_ENV })
+  .on('exit', () => {
+    console.log(process.env.SET_IN_WORKER);  // Prints 'foo'.
+  });
+```
+
+```cjs
+'use strict';
+
 const { Worker, SHARE_ENV } = require('node:worker_threads');
 new Worker('process.env.SET_IN_WORKER = "foo"', { eval: true, env: SHARE_ENV })
   .on('exit', () => {
@@ -557,7 +733,19 @@ to this thread's `Worker` constructor.
 The data is cloned as if using [`postMessage()`][`port.postMessage()`],
 according to the [HTML structured clone algorithm][].
 
-```js
+```mjs
+import { Worker, isMainThread, workerData } from 'node:worker_threads';
+
+if (isMainThread) {
+  const worker = new Worker(new URL(import.meta.url), { workerData: 'Hello, world!' });
+} else {
+  console.log(workerData);  // Prints 'Hello, world!'.
+}
+```
+
+```cjs
+'use strict';
+
 const { Worker, isMainThread, workerData } = require('node:worker_threads');
 
 if (isMainThread) {
@@ -580,7 +768,30 @@ changes:
 Instances of `BroadcastChannel` allow asynchronous one-to-many communication
 with all other `BroadcastChannel` instances bound to the same channel name.
 
-```js
+```mjs
+import {
+  isMainThread,
+  BroadcastChannel,
+  Worker,
+} from 'node:worker_threads';
+
+const bc = new BroadcastChannel('hello');
+
+if (isMainThread) {
+  let c = 0;
+  bc.onmessage = (event) => {
+    console.log(event.data);
+    if (++c === 10) bc.close();
+  };
+  for (let n = 0; n < 10; n++)
+    new Worker(new URL(import.meta.url));
+} else {
+  bc.postMessage('hello from every worker');
+  bc.close();
+}
+```
+
+```cjs
 'use strict';
 
 const {
@@ -681,7 +892,18 @@ The `MessageChannel` has no methods of its own. `new MessageChannel()`
 yields an object with `port1` and `port2` properties, which refer to linked
 [`MessagePort`][] instances.
 
-```js
+```mjs
+import { MessageChannel } from 'node:worker_threads';
+
+const { port1, port2 } = new MessageChannel();
+port1.on('message', (message) => console.log('received', message));
+port2.postMessage({ foo: 'bar' });
+// Prints: received { foo: 'bar' } from the `port1.on('message')` listener
+```
+
+```cjs
+'use strict';
+
 const { MessageChannel } = require('node:worker_threads');
 
 const { port1, port2 } = new MessageChannel();
@@ -720,7 +942,23 @@ added: v10.5.0
 The `'close'` event is emitted once either side of the channel has been
 disconnected.
 
-```js
+```mjs
+import { MessageChannel } from 'node:worker_threads';
+const { port1, port2 } = new MessageChannel();
+
+// Prints:
+//   foobar
+//   closed!
+port2.on('message', (message) => console.log(message));
+port2.on('close', () => console.log('closed!'));
+
+port1.postMessage('foobar');
+port1.close();
+```
+
+```cjs
+'use strict';
+
 const { MessageChannel } = require('node:worker_threads');
 const { port1, port2 } = new MessageChannel();
 
@@ -841,7 +1079,21 @@ In particular, the significant differences to `JSON` are:
   * {net.SocketAddress}es,
   * {X509Certificate}s.
 
-```js
+```mjs
+import { MessageChannel } from 'node:worker_threads';
+const { port1, port2 } = new MessageChannel();
+
+port1.on('message', (message) => console.log(message));
+
+const circularData = {};
+circularData.foo = circularData;
+// Prints: { foo: [Circular] }
+port2.postMessage(circularData);
+```
+
+```cjs
+'use strict';
+
 const { MessageChannel } = require('node:worker_threads');
 const { port1, port2 } = new MessageChannel();
 
@@ -866,7 +1118,33 @@ from either thread. They cannot be listed in `transferList`.
 `value` may still contain `ArrayBuffer` instances that are not in
 `transferList`; in that case, the underlying memory is copied rather than moved.
 
-```js
+```mjs
+import { MessageChannel } from 'node:worker_threads';
+const { port1, port2 } = new MessageChannel();
+
+port1.on('message', (message) => console.log(message));
+
+const uint8Array = new Uint8Array([ 1, 2, 3, 4 ]);
+// This posts a copy of `uint8Array`:
+port2.postMessage(uint8Array);
+// This does not copy data, but renders `uint8Array` unusable:
+port2.postMessage(uint8Array, [ uint8Array.buffer ]);
+
+// The memory for the `sharedUint8Array` is accessible from both the
+// original and the copy received by `.on('message')`:
+const sharedUint8Array = new Uint8Array(new SharedArrayBuffer(4));
+port2.postMessage(sharedUint8Array);
+
+// This transfers a freshly created message port to the receiver.
+// This can be used, for example, to create communication channels between
+// multiple `Worker` threads that are children of the same parent thread.
+const otherChannel = new MessageChannel();
+port2.postMessage({ port: otherChannel.port1 }, [ otherChannel.port1 ]);
+```
+
+```cjs
+'use strict';
+
 const { MessageChannel } = require('node:worker_threads');
 const { port1, port2 } = new MessageChannel();
 
@@ -1105,7 +1383,30 @@ See [`port.postMessage()`][] for more information on how messages are passed,
 and what kind of JavaScript values can be successfully transported through
 the thread barrier.
 
-```js
+```mjs
+import assert from 'node:assert';
+import {
+  Worker, MessageChannel, MessagePort, isMainThread, parentPort,
+} from 'node:worker_threads';
+if (isMainThread) {
+  const worker = new Worker(new URL(import.meta.url));
+  const subChannel = new MessageChannel();
+  worker.postMessage({ hereIsYourPort: subChannel.port1 }, [subChannel.port1]);
+  subChannel.port2.on('message', (value) => {
+    console.log('received:', value);
+  });
+} else {
+  parentPort.once('message', (value) => {
+    assert(value.hereIsYourPort instanceof MessagePort);
+    value.hereIsYourPort.postMessage('the worker is sending this');
+    value.hereIsYourPort.close();
+  });
+}
+```
+
+```cjs
+'use strict';
+
 const assert = require('node:assert');
 const {
   Worker, MessageChannel, MessagePort, isMainThread, parentPort,
@@ -1391,7 +1692,29 @@ stuck in bootstrap. The following examples shows how the worker's entire
 lifetime never accumulates any `idle` time, but is still be able to process
 messages.
 
-```js
+```mjs
+import { Worker, isMainThread, parentPort } from 'node:worker_threads';
+
+if (isMainThread) {
+  const worker = new Worker(new URL(import.meta.url));
+  setInterval(() => {
+    worker.postMessage('hi');
+    console.log(worker.performance.eventLoopUtilization());
+  }, 100).unref();
+} else {
+  parentPort.on('message', () => console.log('msg')).unref();
+  (function r(n) {
+    if (--n < 0) return;
+    const t = Date.now();
+    while (Date.now() - t < 300);
+    setImmediate(r, n);
+  })(10);
+}
+```
+
+```cjs
+'use strict';
+
 const { Worker, isMainThread, parentPort } = require('node:worker_threads');
 
 if (isMainThread) {
@@ -1400,9 +1723,7 @@ if (isMainThread) {
     worker.postMessage('hi');
     console.log(worker.performance.eventLoopUtilization());
   }, 100).unref();
-  return;
+} else {
-}
-
   parentPort.on('message', () => console.log('msg')).unref();
   (function r(n) {
     if (--n < 0) return;
@@ -1410,6 +1731,7 @@ parentPort.on('message', () => console.log('msg')).unref();
     while (Date.now() - t < 300);
     setImmediate(r, n);
   })(10);
+}
 ```
 
 The event loop utilization of a worker is available only after the [`'online'`