doc/api/v8.md - external/github.com/v8/node - Git at Google

 # V8

 <!--introduced_in=v4.0.0-->

 The `v8` module exposes APIs that are specific to the version of [V8][]
 built into the Node.js binary. It can be accessed using:

 ```js
 const v8 = require('v8');
 ```

 The APIs and implementation are subject to change at any time.

 ## `v8.cachedDataVersionTag()`
 <!-- YAML
 added: v8.0.0
 -->

 * Returns: {integer}

 Returns an integer representing a "version tag" derived from the V8 version,
 command line flags and detected CPU features. This is useful for determining
 whether a [`vm.Script`][] `cachedData` buffer is compatible with this instance
 of V8.

 ## `v8.getHeapSpaceStatistics()`
 <!-- YAML
 added: v6.0.0
 changes:
   - version: v7.5.0
     pr-url: https://github.com/nodejs/node/pull/10186
     description: Support values exceeding the 32-bit unsigned integer range.
 -->

 * Returns: {Object[]}

 Returns statistics about the V8 heap spaces, i.e. the segments which make up
 the V8 heap. Neither the ordering of heap spaces, nor the availability of a
 heap space can be guaranteed as the statistics are provided via the V8
 [`GetHeapSpaceStatistics`][] function and may change from one V8 version to the
 next.

 The value returned is an array of objects containing the following properties:

 * `space_name` {string}
 * `space_size` {number}
 * `space_used_size` {number}
 * `space_available_size` {number}
 * `physical_space_size` {number}

 ```json
 [
   {
     "space_name": "new_space",
     "space_size": 2063872,
     "space_used_size": 951112,
     "space_available_size": 80824,
     "physical_space_size": 2063872
   },
   {
     "space_name": "old_space",
     "space_size": 3090560,
     "space_used_size": 2493792,
     "space_available_size": 0,
     "physical_space_size": 3090560
   },
   {
     "space_name": "code_space",
     "space_size": 1260160,
     "space_used_size": 644256,
     "space_available_size": 960,
     "physical_space_size": 1260160
   },
   {
     "space_name": "map_space",
     "space_size": 1094160,
     "space_used_size": 201608,
     "space_available_size": 0,
     "physical_space_size": 1094160
   },
   {
     "space_name": "large_object_space",
     "space_size": 0,
     "space_used_size": 0,
     "space_available_size": 1490980608,
     "physical_space_size": 0
   }
 ]
 ```

 ## `v8.getHeapSnapshot()`
 <!-- YAML
 added: v11.13.0
 -->

 * Returns: {stream.Readable} A Readable Stream containing the V8 heap snapshot

 Generates a snapshot of the current V8 heap and returns a Readable
 Stream that may be used to read the JSON serialized representation.
 This JSON stream format is intended to be used with tools such as
 Chrome DevTools. The JSON schema is undocumented and specific to the
 V8 engine, and may change from one version of V8 to the next.

 ```js
 const stream = v8.getHeapSnapshot();
 stream.pipe(process.stdout);
 ```

 ## `v8.getHeapStatistics()`
 <!-- YAML
 added: v1.0.0
 changes:
   - version: v7.2.0
     pr-url: https://github.com/nodejs/node/pull/8610
     description: Added `malloced_memory`, `peak_malloced_memory`,
                  and `does_zap_garbage`.
   - version: v7.5.0
     pr-url: https://github.com/nodejs/node/pull/10186
     description: Support values exceeding the 32-bit unsigned integer range.
 -->

 * Returns: {Object}

 Returns an object with the following properties:

 * `total_heap_size` {number}
 * `total_heap_size_executable` {number}
 * `total_physical_size` {number}
 * `total_available_size` {number}
 * `used_heap_size` {number}
 * `heap_size_limit` {number}
 * `malloced_memory` {number}
 * `peak_malloced_memory` {number}
 * `does_zap_garbage` {number}
 * `number_of_native_contexts` {number}
 * `number_of_detached_contexts` {number}

 `does_zap_garbage` is a 0/1 boolean, which signifies whether the
 `--zap_code_space` option is enabled or not. This makes V8 overwrite heap
 garbage with a bit pattern. The RSS footprint (resident memory set) gets bigger
 because it continuously touches all heap pages and that makes them less likely
 to get swapped out by the operating system.

 `number_of_native_contexts` The value of native_context is the number of the
 top-level contexts currently active. Increase of this number over time indicates
 a memory leak.

 `number_of_detached_contexts` The value of detached_context is the number
 of contexts that were detached and not yet garbage collected. This number
 being non-zero indicates a potential memory leak.

 <!-- eslint-skip -->
 ```js
 {
   total_heap_size: 7326976,
   total_heap_size_executable: 4194304,
   total_physical_size: 7326976,
   total_available_size: 1152656,
   used_heap_size: 3476208,
   heap_size_limit: 1535115264,
   malloced_memory: 16384,
   peak_malloced_memory: 1127496,
   does_zap_garbage: 0,
   number_of_native_contexts: 1,
   number_of_detached_contexts: 0
 }
 ```

 ## `v8.getHeapCodeStatistics()`
 <!-- YAML
 added: v12.8.0
 -->

 * Returns: {Object}

 Returns an object with the following properties:

 * `code_and_metadata_size` {number}
 * `bytecode_and_metadata_size` {number}
 * `external_script_source_size` {number}

 <!-- eslint-skip -->
 ```js
 {
   code_and_metadata_size: 212208,
   bytecode_and_metadata_size: 161368,
   external_script_source_size: 1410794
 }
 ```

 ## `v8.setFlagsFromString(flags)`
 <!-- YAML
 added: v1.0.0
 -->

 * `flags` {string}

 The `v8.setFlagsFromString()` method can be used to programmatically set
 V8 command line flags. This method should be used with care. Changing settings
 after the VM has started may result in unpredictable behavior, including
 crashes and data loss; or it may simply do nothing.

 The V8 options available for a version of Node.js may be determined by running
 `node --v8-options`.

 Usage:

 ```js
 // Print GC events to stdout for one minute.
 const v8 = require('v8');
 v8.setFlagsFromString('--trace_gc');
 setTimeout(() => { v8.setFlagsFromString('--notrace_gc'); }, 60e3);
 ```

 ## `v8.writeHeapSnapshot([filename])`
 <!-- YAML
 added: v11.13.0
 -->

 * `filename` {string} The file path where the V8 heap snapshot is to be
   saved. If not specified, a file name with the pattern
   `'Heap-${yyyymmdd}-${hhmmss}-${pid}-${thread_id}.heapsnapshot'` will be
   generated, where `{pid}` will be the PID of the Node.js process,
   `{thread_id}` will be `0` when `writeHeapSnapshot()` is called from
   the main Node.js thread or the id of a worker thread.
 * Returns: {string} The filename where the snapshot was saved.

 Generates a snapshot of the current V8 heap and writes it to a JSON
 file. This file is intended to be used with tools such as Chrome
 DevTools. The JSON schema is undocumented and specific to the V8
 engine, and may change from one version of V8 to the next.

 A heap snapshot is specific to a single V8 isolate. When using
 [Worker Threads][], a heap snapshot generated from the main thread will
 not contain any information about the workers, and vice versa.

 ```js
 const { writeHeapSnapshot } = require('v8');
 const {
   Worker,
   isMainThread,
   parentPort
 } = require('worker_threads');

 if (isMainThread) {
   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());
     }
   });
 }
 ```

 ## Serialization API

 The serialization API provides means of serializing JavaScript values in a way
 that is compatible with the [HTML structured clone algorithm][].

 The format is backward-compatible (i.e. safe to store to disk).
 Equal JavaScript values may result in different serialized output.

 ### `v8.serialize(value)`
 <!-- YAML
 added: v8.0.0
 -->

 * `value` {any}
 * Returns: {Buffer}

 Uses a [`DefaultSerializer`][] to serialize `value` into a buffer.

 ### `v8.deserialize(buffer)`
 <!-- YAML
 added: v8.0.0
 -->

 * `buffer` {Buffer|TypedArray|DataView} A buffer returned by [`serialize()`][].

 Uses a [`DefaultDeserializer`][] with default options to read a JS value
 from a buffer.

 ### Class: `v8.Serializer`
 <!-- YAML
 added: v8.0.0
 -->

 #### `new Serializer()`
 Creates a new `Serializer` object.

 #### `serializer.writeHeader()`

 Writes out a header, which includes the serialization format version.

 #### `serializer.writeValue(value)`

 * `value` {any}

 Serializes a JavaScript value and adds the serialized representation to the
 internal buffer.

 This throws an error if `value` cannot be serialized.

 #### `serializer.releaseBuffer()`

 * Returns: {Buffer}

 Returns the stored internal buffer. This serializer should not be used once
 the buffer is released. Calling this method results in undefined behavior
 if a previous write has failed.

 #### `serializer.transferArrayBuffer(id, arrayBuffer)`

 * `id` {integer} A 32-bit unsigned integer.
 * `arrayBuffer` {ArrayBuffer} An `ArrayBuffer` instance.

 Marks an `ArrayBuffer` as having its contents transferred out of band.
 Pass the corresponding `ArrayBuffer` in the deserializing context to
 [`deserializer.transferArrayBuffer()`][].

 #### `serializer.writeUint32(value)`

 * `value` {integer}

 Write a raw 32-bit unsigned integer.
 For use inside of a custom [`serializer._writeHostObject()`][].

 #### `serializer.writeUint64(hi, lo)`

 * `hi` {integer}
 * `lo` {integer}

 Write a raw 64-bit unsigned integer, split into high and low 32-bit parts.
 For use inside of a custom [`serializer._writeHostObject()`][].

 #### `serializer.writeDouble(value)`

 * `value` {number}

 Write a JS `number` value.
 For use inside of a custom [`serializer._writeHostObject()`][].

 #### `serializer.writeRawBytes(buffer)`

 * `buffer` {Buffer|TypedArray|DataView}

 Write raw bytes into the serializer’s internal buffer. The deserializer
 will require a way to compute the length of the buffer.
 For use inside of a custom [`serializer._writeHostObject()`][].

 #### `serializer._writeHostObject(object)`

 * `object` {Object}

 This method is called to write some kind of host object, i.e. an object created
 by native C++ bindings. If it is not possible to serialize `object`, a suitable
 exception should be thrown.

 This method is not present on the `Serializer` class itself but can be provided
 by subclasses.

 #### `serializer._getDataCloneError(message)`

 * `message` {string}

 This method is called to generate error objects that will be thrown when an
 object can not be cloned.

 This method defaults to the [`Error`][] constructor and can be overridden on
 subclasses.

 #### `serializer._getSharedArrayBufferId(sharedArrayBuffer)`

 * `sharedArrayBuffer` {SharedArrayBuffer}

 This method is called when the serializer is going to serialize a
 `SharedArrayBuffer` object. It must return an unsigned 32-bit integer ID for
 the object, using the same ID if this `SharedArrayBuffer` has already been
 serialized. When deserializing, this ID will be passed to
 [`deserializer.transferArrayBuffer()`][].

 If the object cannot be serialized, an exception should be thrown.

 This method is not present on the `Serializer` class itself but can be provided
 by subclasses.

 #### `serializer._setTreatArrayBufferViewsAsHostObjects(flag)`

 * `flag` {boolean} **Default:** `false`

 Indicate whether to treat `TypedArray` and `DataView` objects as
 host objects, i.e. pass them to [`serializer._writeHostObject()`][].

 ### Class: `v8.Deserializer`
 <!-- YAML
 added: v8.0.0
 -->

 #### `new Deserializer(buffer)`

 * `buffer` {Buffer|TypedArray|DataView} A buffer returned by
   [`serializer.releaseBuffer()`][].

 Creates a new `Deserializer` object.

 #### `deserializer.readHeader()`

 Reads and validates a header (including the format version).
 May, for example, reject an invalid or unsupported wire format. In that case,
 an `Error` is thrown.

 #### `deserializer.readValue()`

 Deserializes a JavaScript value from the buffer and returns it.

 #### `deserializer.transferArrayBuffer(id, arrayBuffer)`

 * `id` {integer} A 32-bit unsigned integer.
 * `arrayBuffer` {ArrayBuffer|SharedArrayBuffer} An `ArrayBuffer` instance.

 Marks an `ArrayBuffer` as having its contents transferred out of band.
 Pass the corresponding `ArrayBuffer` in the serializing context to
 [`serializer.transferArrayBuffer()`][] (or return the `id` from
 [`serializer._getSharedArrayBufferId()`][] in the case of `SharedArrayBuffer`s).

 #### `deserializer.getWireFormatVersion()`

 * Returns: {integer}

 Reads the underlying wire format version. Likely mostly to be useful to
 legacy code reading old wire format versions. May not be called before
 `.readHeader()`.

 #### `deserializer.readUint32()`

 * Returns: {integer}

 Read a raw 32-bit unsigned integer and return it.
 For use inside of a custom [`deserializer._readHostObject()`][].

 #### `deserializer.readUint64()`

 * Returns: {integer[]}

 Read a raw 64-bit unsigned integer and return it as an array `[hi, lo]`
 with two 32-bit unsigned integer entries.
 For use inside of a custom [`deserializer._readHostObject()`][].

 #### `deserializer.readDouble()`

 * Returns: {number}

 Read a JS `number` value.
 For use inside of a custom [`deserializer._readHostObject()`][].

 #### `deserializer.readRawBytes(length)`

 * `length` {integer}
 * Returns: {Buffer}

 Read raw bytes from the deserializer’s internal buffer. The `length` parameter
 must correspond to the length of the buffer that was passed to
 [`serializer.writeRawBytes()`][].
 For use inside of a custom [`deserializer._readHostObject()`][].

 #### `deserializer._readHostObject()`

 This method is called to read some kind of host object, i.e. an object that is
 created by native C++ bindings. If it is not possible to deserialize the data,
 a suitable exception should be thrown.

 This method is not present on the `Deserializer` class itself but can be
 provided by subclasses.

 ### Class: `v8.DefaultSerializer`
 <!-- YAML
 added: v8.0.0
 -->

 A subclass of [`Serializer`][] that serializes `TypedArray`
 (in particular [`Buffer`][]) and `DataView` objects as host objects, and only
 stores the part of their underlying `ArrayBuffer`s that they are referring to.

 ### Class: `v8.DefaultDeserializer`
 <!-- YAML
 added: v8.0.0
 -->

 A subclass of [`Deserializer`][] corresponding to the format written by
 [`DefaultSerializer`][].

 [`Buffer`]: buffer.html
 [`DefaultDeserializer`]: #v8_class_v8_defaultdeserializer
 [`DefaultSerializer`]: #v8_class_v8_defaultserializer
 [`Deserializer`]: #v8_class_v8_deserializer
 [`Error`]: errors.html#errors_class_error
 [`GetHeapSpaceStatistics`]: https://v8docs.nodesource.com/node-13.2/d5/dda/classv8_1_1_isolate.html#ac673576f24fdc7a33378f8f57e1d13a4
 [`Serializer`]: #v8_class_v8_serializer
 [`deserializer._readHostObject()`]: #v8_deserializer_readhostobject
 [`deserializer.transferArrayBuffer()`]: #v8_deserializer_transferarraybuffer_id_arraybuffer
 [`serialize()`]: #v8_v8_serialize_value
 [`serializer._getSharedArrayBufferId()`]: #v8_serializer_getsharedarraybufferid_sharedarraybuffer
 [`serializer._writeHostObject()`]: #v8_serializer_writehostobject_object
 [`serializer.releaseBuffer()`]: #v8_serializer_releasebuffer
 [`serializer.transferArrayBuffer()`]: #v8_serializer_transferarraybuffer_id_arraybuffer
 [`serializer.writeRawBytes()`]: #v8_serializer_writerawbytes_buffer
 [`vm.Script`]: vm.html#vm_constructor_new_vm_script_code_options
 [HTML structured clone algorithm]: https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API/Structured_clone_algorithm
 [V8]: https://developers.google.com/v8/
 [Worker Threads]: worker_threads.html
	# V8

	<!--introduced_in=v4.0.0-->

	The `v8` module exposes APIs that are specific to the version of [V8][]
	built into the Node.js binary. It can be accessed using:

	```js
	const v8 = require('v8');
	```

	The APIs and implementation are subject to change at any time.

	## `v8.cachedDataVersionTag()`
	<!-- YAML
	added: v8.0.0
	-->

	* Returns: {integer}

	Returns an integer representing a "version tag" derived from the V8 version,
	command line flags and detected CPU features. This is useful for determining
	whether a [`vm.Script`][] `cachedData` buffer is compatible with this instance
	of V8.

	## `v8.getHeapSpaceStatistics()`
	<!-- YAML
	added: v6.0.0
	changes:
	- version: v7.5.0
	pr-url: https://github.com/nodejs/node/pull/10186
	description: Support values exceeding the 32-bit unsigned integer range.
	-->

	* Returns: {Object[]}

	Returns statistics about the V8 heap spaces, i.e. the segments which make up
	the V8 heap. Neither the ordering of heap spaces, nor the availability of a
	heap space can be guaranteed as the statistics are provided via the V8
	[`GetHeapSpaceStatistics`][] function and may change from one V8 version to the
	next.

	The value returned is an array of objects containing the following properties:

	* `space_name` {string}
	* `space_size` {number}
	* `space_used_size` {number}
	* `space_available_size` {number}
	* `physical_space_size` {number}

	```json
	[
	{
	"space_name": "new_space",
	"space_size": 2063872,
	"space_used_size": 951112,
	"space_available_size": 80824,
	"physical_space_size": 2063872
	},
	{
	"space_name": "old_space",
	"space_size": 3090560,
	"space_used_size": 2493792,
	"space_available_size": 0,
	"physical_space_size": 3090560
	},
	{
	"space_name": "code_space",
	"space_size": 1260160,
	"space_used_size": 644256,
	"space_available_size": 960,
	"physical_space_size": 1260160
	},
	{
	"space_name": "map_space",
	"space_size": 1094160,
	"space_used_size": 201608,
	"space_available_size": 0,
	"physical_space_size": 1094160
	},
	{
	"space_name": "large_object_space",
	"space_size": 0,
	"space_used_size": 0,
	"space_available_size": 1490980608,
	"physical_space_size": 0
	}
	]
	```

	## `v8.getHeapSnapshot()`
	<!-- YAML
	added: v11.13.0
	-->

	* Returns: {stream.Readable} A Readable Stream containing the V8 heap snapshot

	Generates a snapshot of the current V8 heap and returns a Readable
	Stream that may be used to read the JSON serialized representation.
	This JSON stream format is intended to be used with tools such as
	Chrome DevTools. The JSON schema is undocumented and specific to the
	V8 engine, and may change from one version of V8 to the next.

	```js
	const stream = v8.getHeapSnapshot();
	stream.pipe(process.stdout);
	```

	## `v8.getHeapStatistics()`
	<!-- YAML
	added: v1.0.0
	changes:
	- version: v7.2.0
	pr-url: https://github.com/nodejs/node/pull/8610
	description: Added `malloced_memory`, `peak_malloced_memory`,
	and `does_zap_garbage`.
	- version: v7.5.0
	pr-url: https://github.com/nodejs/node/pull/10186
	description: Support values exceeding the 32-bit unsigned integer range.
	-->

	* Returns: {Object}

	Returns an object with the following properties:

	* `total_heap_size` {number}
	* `total_heap_size_executable` {number}
	* `total_physical_size` {number}
	* `total_available_size` {number}
	* `used_heap_size` {number}
	* `heap_size_limit` {number}
	* `malloced_memory` {number}
	* `peak_malloced_memory` {number}
	* `does_zap_garbage` {number}
	* `number_of_native_contexts` {number}
	* `number_of_detached_contexts` {number}

	`does_zap_garbage` is a 0/1 boolean, which signifies whether the
	`--zap_code_space` option is enabled or not. This makes V8 overwrite heap
	garbage with a bit pattern. The RSS footprint (resident memory set) gets bigger
	because it continuously touches all heap pages and that makes them less likely
	to get swapped out by the operating system.

	`number_of_native_contexts` The value of native_context is the number of the
	top-level contexts currently active. Increase of this number over time indicates
	a memory leak.

	`number_of_detached_contexts` The value of detached_context is the number
	of contexts that were detached and not yet garbage collected. This number
	being non-zero indicates a potential memory leak.

	<!-- eslint-skip -->
	```js
	{
	total_heap_size: 7326976,
	total_heap_size_executable: 4194304,
	total_physical_size: 7326976,
	total_available_size: 1152656,
	used_heap_size: 3476208,
	heap_size_limit: 1535115264,
	malloced_memory: 16384,
	peak_malloced_memory: 1127496,
	does_zap_garbage: 0,
	number_of_native_contexts: 1,
	number_of_detached_contexts: 0
	}
	```

	## `v8.getHeapCodeStatistics()`
	<!-- YAML
	added: v12.8.0
	-->

	* Returns: {Object}

	Returns an object with the following properties:

	* `code_and_metadata_size` {number}
	* `bytecode_and_metadata_size` {number}
	* `external_script_source_size` {number}

	<!-- eslint-skip -->
	```js
	{
	code_and_metadata_size: 212208,
	bytecode_and_metadata_size: 161368,
	external_script_source_size: 1410794
	}
	```

	## `v8.setFlagsFromString(flags)`
	<!-- YAML
	added: v1.0.0
	-->

	* `flags` {string}

	The `v8.setFlagsFromString()` method can be used to programmatically set
	V8 command line flags. This method should be used with care. Changing settings
	after the VM has started may result in unpredictable behavior, including
	crashes and data loss; or it may simply do nothing.

	The V8 options available for a version of Node.js may be determined by running
	`node --v8-options`.

	Usage:

	```js
	// Print GC events to stdout for one minute.
	const v8 = require('v8');
	v8.setFlagsFromString('--trace_gc');
	setTimeout(() => { v8.setFlagsFromString('--notrace_gc'); }, 60e3);
	```

	## `v8.writeHeapSnapshot([filename])`
	<!-- YAML
	added: v11.13.0
	-->

	* `filename` {string} The file path where the V8 heap snapshot is to be
	saved. If not specified, a file name with the pattern
	`'Heap-${yyyymmdd}-${hhmmss}-${pid}-${thread_id}.heapsnapshot'` will be
	generated, where `{pid}` will be the PID of the Node.js process,
	`{thread_id}` will be `0` when `writeHeapSnapshot()` is called from
	the main Node.js thread or the id of a worker thread.
	* Returns: {string} The filename where the snapshot was saved.

	Generates a snapshot of the current V8 heap and writes it to a JSON
	file. This file is intended to be used with tools such as Chrome
	DevTools. The JSON schema is undocumented and specific to the V8
	engine, and may change from one version of V8 to the next.

	A heap snapshot is specific to a single V8 isolate. When using
	[Worker Threads][], a heap snapshot generated from the main thread will
	not contain any information about the workers, and vice versa.

	```js
	const { writeHeapSnapshot } = require('v8');
	const {
	Worker,
	isMainThread,
	parentPort
	} = require('worker_threads');

	if (isMainThread) {
	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());
	}
	});
	}
	```

	## Serialization API

	The serialization API provides means of serializing JavaScript values in a way
	that is compatible with the [HTML structured clone algorithm][].

	The format is backward-compatible (i.e. safe to store to disk).
	Equal JavaScript values may result in different serialized output.

	### `v8.serialize(value)`
	<!-- YAML
	added: v8.0.0
	-->

	* `value` {any}
	* Returns: {Buffer}

	Uses a [`DefaultSerializer`][] to serialize `value` into a buffer.

	### `v8.deserialize(buffer)`
	<!-- YAML
	added: v8.0.0
	-->

	* `buffer` {Buffer\|TypedArray\|DataView} A buffer returned by [`serialize()`][].

	Uses a [`DefaultDeserializer`][] with default options to read a JS value
	from a buffer.

	### Class: `v8.Serializer`
	<!-- YAML
	added: v8.0.0
	-->

	#### `new Serializer()`
	Creates a new `Serializer` object.

	#### `serializer.writeHeader()`

	Writes out a header, which includes the serialization format version.

	#### `serializer.writeValue(value)`

	* `value` {any}

	Serializes a JavaScript value and adds the serialized representation to the
	internal buffer.

	This throws an error if `value` cannot be serialized.

	#### `serializer.releaseBuffer()`

	* Returns: {Buffer}

	Returns the stored internal buffer. This serializer should not be used once
	the buffer is released. Calling this method results in undefined behavior
	if a previous write has failed.

	#### `serializer.transferArrayBuffer(id, arrayBuffer)`

	* `id` {integer} A 32-bit unsigned integer.
	* `arrayBuffer` {ArrayBuffer} An `ArrayBuffer` instance.

	Marks an `ArrayBuffer` as having its contents transferred out of band.
	Pass the corresponding `ArrayBuffer` in the deserializing context to
	[`deserializer.transferArrayBuffer()`][].

	#### `serializer.writeUint32(value)`

	* `value` {integer}

	Write a raw 32-bit unsigned integer.
	For use inside of a custom [`serializer._writeHostObject()`][].

	#### `serializer.writeUint64(hi, lo)`

	* `hi` {integer}
	* `lo` {integer}

	Write a raw 64-bit unsigned integer, split into high and low 32-bit parts.
	For use inside of a custom [`serializer._writeHostObject()`][].

	#### `serializer.writeDouble(value)`

	* `value` {number}

	Write a JS `number` value.
	For use inside of a custom [`serializer._writeHostObject()`][].

	#### `serializer.writeRawBytes(buffer)`

	* `buffer` {Buffer\|TypedArray\|DataView}

	Write raw bytes into the serializer’s internal buffer. The deserializer
	will require a way to compute the length of the buffer.
	For use inside of a custom [`serializer._writeHostObject()`][].

	#### `serializer._writeHostObject(object)`

	* `object` {Object}

	This method is called to write some kind of host object, i.e. an object created
	by native C++ bindings. If it is not possible to serialize `object`, a suitable
	exception should be thrown.

	This method is not present on the `Serializer` class itself but can be provided
	by subclasses.

	#### `serializer._getDataCloneError(message)`

	* `message` {string}

	This method is called to generate error objects that will be thrown when an
	object can not be cloned.

	This method defaults to the [`Error`][] constructor and can be overridden on
	subclasses.

	#### `serializer._getSharedArrayBufferId(sharedArrayBuffer)`

	* `sharedArrayBuffer` {SharedArrayBuffer}

	This method is called when the serializer is going to serialize a
	`SharedArrayBuffer` object. It must return an unsigned 32-bit integer ID for
	the object, using the same ID if this `SharedArrayBuffer` has already been
	serialized. When deserializing, this ID will be passed to
	[`deserializer.transferArrayBuffer()`][].

	If the object cannot be serialized, an exception should be thrown.

	This method is not present on the `Serializer` class itself but can be provided
	by subclasses.

	#### `serializer._setTreatArrayBufferViewsAsHostObjects(flag)`

	* `flag` {boolean} Default: `false`

	Indicate whether to treat `TypedArray` and `DataView` objects as
	host objects, i.e. pass them to [`serializer._writeHostObject()`][].

	### Class: `v8.Deserializer`
	<!-- YAML
	added: v8.0.0
	-->

	#### `new Deserializer(buffer)`

	* `buffer` {Buffer\|TypedArray\|DataView} A buffer returned by
	[`serializer.releaseBuffer()`][].

	Creates a new `Deserializer` object.

	#### `deserializer.readHeader()`

	Reads and validates a header (including the format version).
	May, for example, reject an invalid or unsupported wire format. In that case,
	an `Error` is thrown.

	#### `deserializer.readValue()`

	Deserializes a JavaScript value from the buffer and returns it.

	#### `deserializer.transferArrayBuffer(id, arrayBuffer)`

	* `id` {integer} A 32-bit unsigned integer.
	* `arrayBuffer` {ArrayBuffer\|SharedArrayBuffer} An `ArrayBuffer` instance.

	Marks an `ArrayBuffer` as having its contents transferred out of band.
	Pass the corresponding `ArrayBuffer` in the serializing context to
	[`serializer.transferArrayBuffer()`][] (or return the `id` from
	[`serializer._getSharedArrayBufferId()`][] in the case of `SharedArrayBuffer`s).

	#### `deserializer.getWireFormatVersion()`

	* Returns: {integer}

	Reads the underlying wire format version. Likely mostly to be useful to
	legacy code reading old wire format versions. May not be called before
	`.readHeader()`.

	#### `deserializer.readUint32()`

	* Returns: {integer}

	Read a raw 32-bit unsigned integer and return it.
	For use inside of a custom [`deserializer._readHostObject()`][].

	#### `deserializer.readUint64()`

	* Returns: {integer[]}

	Read a raw 64-bit unsigned integer and return it as an array `[hi, lo]`
	with two 32-bit unsigned integer entries.
	For use inside of a custom [`deserializer._readHostObject()`][].

	#### `deserializer.readDouble()`

	* Returns: {number}

	Read a JS `number` value.
	For use inside of a custom [`deserializer._readHostObject()`][].

	#### `deserializer.readRawBytes(length)`

	* `length` {integer}
	* Returns: {Buffer}

	Read raw bytes from the deserializer’s internal buffer. The `length` parameter
	must correspond to the length of the buffer that was passed to
	[`serializer.writeRawBytes()`][].
	For use inside of a custom [`deserializer._readHostObject()`][].

	#### `deserializer._readHostObject()`

	This method is called to read some kind of host object, i.e. an object that is
	created by native C++ bindings. If it is not possible to deserialize the data,
	a suitable exception should be thrown.

	This method is not present on the `Deserializer` class itself but can be
	provided by subclasses.

	### Class: `v8.DefaultSerializer`
	<!-- YAML
	added: v8.0.0
	-->

	A subclass of [`Serializer`][] that serializes `TypedArray`
	(in particular [`Buffer`][]) and `DataView` objects as host objects, and only
	stores the part of their underlying `ArrayBuffer`s that they are referring to.

	### Class: `v8.DefaultDeserializer`
	<!-- YAML
	added: v8.0.0
	-->

	A subclass of [`Deserializer`][] corresponding to the format written by
	[`DefaultSerializer`][].

	[`Buffer`]: buffer.html
	[`DefaultDeserializer`]: #v8_class_v8_defaultdeserializer
	[`DefaultSerializer`]: #v8_class_v8_defaultserializer
	[`Deserializer`]: #v8_class_v8_deserializer
	[`Error`]: errors.html#errors_class_error
	[`GetHeapSpaceStatistics`]: https://v8docs.nodesource.com/node-13.2/d5/dda/classv8_1_1_isolate.html#ac673576f24fdc7a33378f8f57e1d13a4
	[`Serializer`]: #v8_class_v8_serializer
	[`deserializer._readHostObject()`]: #v8_deserializer_readhostobject
	[`deserializer.transferArrayBuffer()`]: #v8_deserializer_transferarraybuffer_id_arraybuffer
	[`serialize()`]: #v8_v8_serialize_value
	[`serializer._getSharedArrayBufferId()`]: #v8_serializer_getsharedarraybufferid_sharedarraybuffer
	[`serializer._writeHostObject()`]: #v8_serializer_writehostobject_object
	[`serializer.releaseBuffer()`]: #v8_serializer_releasebuffer
	[`serializer.transferArrayBuffer()`]: #v8_serializer_transferarraybuffer_id_arraybuffer
	[`serializer.writeRawBytes()`]: #v8_serializer_writerawbytes_buffer
	[`vm.Script`]: vm.html#vm_constructor_new_vm_script_code_options
	[HTML structured clone algorithm]: https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API/Structured_clone_algorithm
	[V8]: https://developers.google.com/v8/
	[Worker Threads]: worker_threads.html