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‎doc/api/v8.md‎
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+217-14Lines changed: 217 additions & 14 deletions
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@@ -7,7 +7,11 @@
 The `node:v8` module exposes APIs that are specific to the version of [V8][]
 built into the Node.js binary. It can be accessed using:
 
-```js
+```mjs
+import v8 from 'node:v8';
+```
+
+```cjs
 const v8 = require('node:v8');
 ```
 
@@ -92,9 +96,18 @@ terminating the process.
 Generating a snapshot is a synchronous operation which blocks the event loop
 for a duration depending on the heap size.
 
+```mjs
+// Print heap snapshot to the console
+import { getHeapSnapshot } from 'node:v8';
+import process from 'node:process';
+const stream = getHeapSnapshot();
+stream.pipe(process.stdout);
+```
+
 ```js
 // Print heap snapshot to the console
 const v8 = require('node:v8');
+const process = require('node:process');
 const stream = v8.getHeapSnapshot();
 stream.pipe(process.stdout);
 ```
@@ -467,11 +480,70 @@ The V8 options available for a version of Node.js may be determined by running
 
 Usage:
 
-```js
-// Print GC events to stdout for one minute.
-const v8 = require('node:v8');
-v8.setFlagsFromString('--trace_gc');
-setTimeout(() => { v8.setFlagsFromString('--notrace_gc'); }, 60e3);
+```mjs
+import { setFlagsFromString } from 'node:v8';
+import { setInterval } from 'node:timers';
+
+// setFlagsFromString to trace garbage collection events
+setFlagsFromString('--trace-gc');
+
+// Trigger GC events by using some memory
+let arrays = [];
+const interval = setInterval(() => {
+  for (let i = 0; i < 500; i++) {
+    arrays.push(new Array(10000).fill(Math.random()));
+  }
+
+  if (arrays.length > 5000) {
+    arrays = arrays.slice(-1000);
+  }
+
+  console.log(`\n* Created ${arrays.length} arrays\n`);
+}, 100);
+
+// setFlagsFromString to stop tracing GC events after 1.5 seconds
+setTimeout(() => {
+  setFlagsFromString('--notrace-gc');
+  console.log('\nStopped tracing!\n');
+}, 1500);
+
+// Stop triggering GC events altogether after 2.5 seconds
+setTimeout(() => {
+  clearInterval(interval);
+}, 2500);
+```
+
+```cjs
+const { setFlagsFromString } = require('node:v8');
+const { setInterval } = require('node:timers');
+
+// setFlagsFromString to trace garbage collection events
+setFlagsFromString('--trace-gc');
+
+// Trigger GC events by using some memory
+let arrays = [];
+const interval = setInterval(() => {
+  for (let i = 0; i < 500; i++) {
+    arrays.push(new Array(10000).fill(Math.random()));
+  }
+
+  if (arrays.length > 5000) {
+    arrays = arrays.slice(-1000);
+  }
+
+  console.log(`\n* Created ${arrays.length} arrays\n`);
+}, 100);
+
+// setFlagsFromString to stop tracing GC events after 1.5 seconds
+setTimeout(() => {
+  console.log('\nStopped tracing!\n');
+  setFlagsFromString('--notrace-gc');
+}, 1500);
+
+// Stop triggering GC events altogether after 2.5 seconds
+setTimeout(() => {
+  clearInterval(interval);
+}, 2500);
 ```
 
 ## `v8.stopCoverage()`
@@ -551,13 +623,37 @@ terminating the process.
 Generating a snapshot is a synchronous operation which blocks the event loop
 for a duration depending on the heap size.
 
-```js
+```mjs
+import { writeHeapSnapshot } from 'node:v8';
+import { Worker, isMainThread, parentPort } from 'node:worker_threads';
+import { fileURLToPath } from 'node:url';
+
+if (isMainThread) {
+  const __filename = fileURLToPath(import.meta.url);
+  const worker = new Worker(__filename);
+
+  worker.once('message', (filename) => {
+    console.log(`worker heapdump: ${filename}`);
+    // Now get a heapdump for the main thread.
+    console.log(`main thread heapdump: ${writeHeapSnapshot()}`);
+  });
+
+  // Tell the worker to create a heapdump.
+  worker.postMessage('heapdump');
+} else {
+  parentPort.once('message', (message) => {
+    if (message === 'heapdump') {
+      // Generate a heapdump for the worker
+      // and return the filename to the parent.
+      parentPort.postMessage(writeHeapSnapshot());
+    }
+  });
+}
+```
+
+```cjs
 const { writeHeapSnapshot } = require('node:v8');
-const {
-  Worker,
-  isMainThread,
-  parentPort,
-} = require('node:worker_threads');
+const { Worker, isMainThread, parentPort } = require('node:worker_threads');
 
 if (isMainThread) {
   const worker = new Worker(__filename);
@@ -903,6 +999,71 @@ const stopHookSet = promiseHooks.createHook({
   after,
 });
 
+// Trigger the hooks by using promises
+const promiseLog = (word) => Promise.resolve(word).then(console.log);
+promiseLog('Hello');
+promiseLog('World');
+
+// To stop a hook, call the function returned at its creation.
+stopWatchingInits();
+stopWatchingSettleds();
+stopWatchingBefores();
+stopWatchingAfters();
+stopHookSet();
+```
+
+```cjs
+const { promiseHooks } = require('node:v8');
+
+// There are four lifecycle events produced by promises:
+
+// The `init` event represents the creation of a promise. This could be a
+// direct creation such as with `new Promise(...)` or a continuation such
+// as `then()` or `catch()`. It also happens whenever an async function is
+// called or does an `await`. If a continuation promise is created, the
+// `parent` will be the promise it is a continuation from.
+function init(promise, parent) {
+  console.log('a promise was created', { promise, parent });
+}
+
+// The `settled` event happens when a promise receives a resolution or
+// rejection value. This may happen synchronously such as when using
+// `Promise.resolve()` on non-promise input.
+function settled(promise) {
+  console.log('a promise resolved or rejected', { promise });
+}
+
+// The `before` event runs immediately before a `then()` or `catch()` handler
+// runs or an `await` resumes execution.
+function before(promise) {
+  console.log('a promise is about to call a then handler', { promise });
+}
+
+// The `after` event runs immediately after a `then()` handler runs or when
+// an `await` begins after resuming from another.
+function after(promise) {
+  console.log('a promise is done calling a then handler', { promise });
+}
+
+// Lifecycle hooks may be started and stopped individually
+const stopWatchingInits = promiseHooks.onInit(init);
+const stopWatchingSettleds = promiseHooks.onSettled(settled);
+const stopWatchingBefores = promiseHooks.onBefore(before);
+const stopWatchingAfters = promiseHooks.onAfter(after);
+
+// Or they may be started and stopped in groups
+const stopHookSet = promiseHooks.createHook({
+  init,
+  settled,
+  before,
+  after,
+});
+
+// Trigger the hooks by using promises
+const promisePrint = (word) => Promise.resolve(word).then(console.log);
+promisePrint('Hello');
+promisePrint('World');
+
 // To stop a hook, call the function returned at its creation.
 stopWatchingInits();
 stopWatchingSettleds();
@@ -1396,7 +1557,16 @@ is as follows.
 
 Here's an example.
 
-```js
+```mjs
+import { GCProfiler } from 'node:v8';
+const profiler = new GCProfiler();
+profiler.start();
+setTimeout(() => {
+  console.log(profiler.stop());
+}, 1000);
+```
+
+```cjs
 const { GCProfiler } = require('node:v8');
 const profiler = new GCProfiler();
 profiler.start();
@@ -1501,8 +1671,37 @@ otherwise, it returns false.
 If this method returns false, that does not mean that the string contains some characters not in `Latin-1/ISO-8859-1`.
 Sometimes a `Latin-1` string may also be represented as `UTF16`.
 
-```js
+```mjs
+import { isStringOneByteRepresentation } from 'node:v8';
+import { Buffer } from 'node:buffer';
+
+const Encoding = {
+  latin1: 1,
+  utf16le: 2,
+};
+const buffer = Buffer.alloc(100);
+function writeString(input) {
+  if (isStringOneByteRepresentation(input)) {
+    console.log(`input: '${input}'`);
+    buffer.writeUint8(Encoding.latin1);
+    buffer.writeUint32LE(input.length, 1);
+    buffer.write(input, 5, 'latin1');
+    console.log(`decoded: '${buffer.toString('latin1', 5, 5 + input.length)}'\n`);
+  } else {
+    console.log(`input: '${input}'`);
+    buffer.writeUint8(Encoding.utf16le);
+    buffer.writeUint32LE(input.length * 2, 1);
+    buffer.write(input, 5, 'utf16le');
+    console.log(`decoded: '${buffer.toString('utf16le', 5, 5 + input.length * 2)}'`);
+  }
+}
+writeString('hello');
+writeString('你好');
+```
+
+```cjs
 const { isStringOneByteRepresentation } = require('node:v8');
+const { Buffer } = require('node:buffer');
 
 const Encoding = {
   latin1: 1,
@@ -1511,13 +1710,17 @@ const Encoding = {
 const buffer = Buffer.alloc(100);
 function writeString(input) {
   if (isStringOneByteRepresentation(input)) {
+    console.log(`input: '${input}'`);
     buffer.writeUint8(Encoding.latin1);
     buffer.writeUint32LE(input.length, 1);
     buffer.write(input, 5, 'latin1');
+    console.log(`decoded: '${buffer.toString('latin1', 5, 5 + input.length)}'\n`);
   } else {
+    console.log(`input: '${input}'`);
     buffer.writeUint8(Encoding.utf16le);
     buffer.writeUint32LE(input.length * 2, 1);
     buffer.write(input, 5, 'utf16le');
+    console.log(`decoded: '${buffer.toString('utf16le', 5, 5 + input.length * 2)}'`);
   }
 }
 writeString('hello');