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<!DOCTYPE html><html lang="en"><head> <meta charset="utf-8"> <meta name="viewport" content="width=device-width"> <title>V8 | Node.js v12.10.0 Documentation</title> <link rel="stylesheet" href="data:text/css;base64,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"> <link rel="stylesheet" href="data:text/css;base64,/*--------------------- Layout and Typography ----------------------------*/
html {
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* {
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body {
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h1 { font-size: 2.5rem }
h2 { font-size: 2rem }
h3 { font-size: 1.75rem }
h4 { font-size: 1.5rem }
h5 { font-size: 1.25rem }
h6 { font-size: 1rem }

h1, h2, h3, h4, h5, h6 {
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pre, tt, code, .pre, span.type, a.type {
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#content {
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a, a:link, a:active {
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  padding: 1px 3px;
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a:hover, a:focus {
  color: #fff;
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}

strong {
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code a:hover {
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}

em code {
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}

#changelog #gtoc {
  display: none;
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#gtoc {
  margin-top: .5rem;
  margin-bottom: 1rem;
}

#gtoc ul {
  list-style: none;
  margin-left: 0;
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#gtoc > ul > li {
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  margin-right: 0.4rem;
  padding-right: 0.4rem;
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#gtoc > ul > li:last-child {
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  margin-right: 0;
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li.version-picker {
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li.version-picker:hover > a {
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li.version-picker:hover > ol {
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li.version-picker a span {
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ol.version-picker {
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  border-radius: 0 0 2px 2px;
  display: none;
  list-style: none;
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  right: 0;
  top: 1.25rem;
  width: 100%;
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#gtoc ol.version-picker li {
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ol.version-picker li a {
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ol.version-picker li:last-child a {
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.line {
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.api_stability {
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.api_stability * {
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.api_stability a {
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.api_stability a:hover, .api_stability a:active, .api_stability a:focus {
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.api_stability a code {
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.api_stability_0 {
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.api_stability_1 {
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.api_stability_2 {
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.api_metadata {
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abbr {
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p {
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}

#apicontent > *:last-child {
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}

table {
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  margin: 0 0 1.5rem 0;
}

th, td {
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  padding: .75rem 1rem .75rem 1rem;
  vertical-align: top;
}

th {
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}

ol, ul, dl {
  margin: 0 0 .6rem 0;
  padding: 0;
}

ol ul, ol ol, ol dl, ul ul, ul ol, ul dl, dl ul, dl ol, dl dl {
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}

ul, ol {
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}

dl dt {
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dl dd {
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dd + dt.pre {
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#apicontent {
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}

#apicontent .line {
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  margin: 1rem 1rem .95rem;
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}

h2 + h2 {
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}

h3 + h3 {
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h2, h3, h4, h5 {
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.srclink {
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h1 span, h2 span, h3 span, h4 span {
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h1 span:hover, h2 span:hover, h3 span:hover, h4 span:hover {
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h1 span a, h2 span a, h3 span a, h4 span a {
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pre, tt, code {
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.pre {
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pre {
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}

pre > code {
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pre + h3 {
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code.pre {
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#intro {
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  margin-left: 1rem;
}

#intro a {
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}

hr {
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  margin: 0 0 1rem 0;
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#toc h2 {
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}

#toc p {
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#toc ul a {
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#toc ul li {
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}

#toc li > ul {
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#toc .stability_0::after {
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  color: #fff;
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  margin-left: .25rem;
  padding: 1px 3px;
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}

#apicontent li {
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}

#apicontent li:last-child {
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tt, code {
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  border-radius: 2px;
  padding: 1px 3px;
}

.api_stability code {
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}

a code {
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  background: inherit;
  padding: 0;
}

.type {
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}

#column1.interior {
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  -webkit-padding-start: 1.5rem;
}

#column2.interior {
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  background: #333;
  position: fixed;
  left: 0;
  top: 0;
  bottom: 0;
  overflow-x: hidden;
  overflow-y: scroll;
}

#column2 ul {
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  margin: .9rem 0 .5rem;
  background: #333;
}

#column2 > :first-child {
  margin: 1.25rem;
  font-size: 1.5rem;
}

#column2 > ul:nth-child(2) {
  margin: 1.25rem 0 .5rem;
}

#column2 > ul:last-child {
  margin: .9rem 0 1.25rem;
}

#column2 ul li {
  padding-left: 1.25rem;
  margin-bottom: .5rem;
  padding-bottom: .5rem;
}

#column2 .line {
  margin: 0 .5rem;
  background-color: #707070;
}

#column2 ul li:last-child {
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}

#column2 ul li a {
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}

#column2 ul li a.active, #column2 ul li a.active:hover,
#column2 ul li a.active:focus {
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  border-radius: 0;
  border-bottom: 1px solid #43853d;
  background: none;
}

#intro a:hover, #intro a:focus,
#column2 ul li a:hover, #column2 ul li a:focus {
  color: #fff;
  background: none;
}

span > .mark, span > .mark:visited {
  color: #707070;
  position: absolute;
  top: 0px;
  right: 0px;
}

span > .mark:hover, span > .mark:focus, span > .mark:active {
  color: #43853d;
  background: none;
}

th > *:last-child, td > *:last-child {
  margin-bottom: 0;
}

.changelog > summary {
  margin: .5rem 0;
  padding: .5rem 0;
  cursor: pointer;
}

/* simpler clearfix */
.clearfix:after {
  content: ".";
  display: block;
  height: 0;
  clear: both;
  visibility: hidden;
}

.github_icon {
  vertical-align: middle;
  margin: -2px 3px 0 0;
}

@media only screen and (max-width: 1024px) {
  #content {
    overflow: visible;
  }
  #column1.interior {
    margin-left: 0;
    padding-left: .5rem;
    padding-right: .5rem;
    width: auto;
    overflow-y: visible;
  }
  #column2 {
    display: none;
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}

@media print {
  html {
    height: auto;
    font-size: 0.75em;
  }
  #column2.interior {
    display: none;
  }
  #column1.interior {
    margin-left: 0px;
    padding: 0px;
    overflow-y: auto;
  }
  .api_metadata,
  #toc,
  .srclink,
  #gtoc,
  .mark {
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  }
  h1 {
    font-size: 2rem;
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  h2 {
    font-size: 1.75rem;
  }
  h3 {
    font-size: 1.5rem;
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  h4 {
    font-size: 1.3rem;
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  h5 {
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  h6 {
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  .api_stability {
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  .api_stability a {
    text-decoration: none;
  }
  a {
    color: inherit;
  }
  #apicontent {
    overflow: hidden;
  }
}
"> <link rel="stylesheet" href="data:text/css;base64,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"> <link rel="canonical" href="https://nodejs.org/api/v8.html"> </head> <body class="alt apidoc" id="api-section-v8"> <div id="content" class="clearfix"> <div id="column2" class="interior"> <div id="intro" class="interior"> <a href="https://nodejs.org/" title="Go back to the home page"> Node.js </a> </div> <ul> <li><a href="https://nodejs.org/api/documentation.html" class="nav-documentation">About these Docs</a></li> <li><a href="https://nodejs.org/api/synopsis.html" class="nav-synopsis">Usage & Example</a></li> </ul> <div class="line"></div> <ul> <li><a href="https://nodejs.org/api/assert.html" class="nav-assert">Assertion Testing</a></li> <li><a href="https://nodejs.org/api/async_hooks.html" class="nav-async_hooks">Async Hooks</a></li> <li><a href="https://nodejs.org/api/buffer.html" class="nav-buffer">Buffer</a></li> <li><a href="https://nodejs.org/api/addons.html" class="nav-addons">C++ Addons</a></li> <li><a href="https://nodejs.org/api/n-api.html" class="nav-n-api">C/C++ Addons - N-API</a></li> <li><a href="https://nodejs.org/api/child_process.html" class="nav-child_process">Child Processes</a></li> <li><a href="https://nodejs.org/api/cluster.html" class="nav-cluster">Cluster</a></li> <li><a href="https://nodejs.org/api/cli.html" class="nav-cli">Command Line Options</a></li> <li><a href="https://nodejs.org/api/console.html" class="nav-console">Console</a></li> <li><a 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href="#v8_v8_setflagsfromstring_flags">v8.setFlagsFromString(flags)</a></li> <li><a href="#v8_v8_writeheapsnapshot_filename">v8.writeHeapSnapshot([filename])</a></li> <li> <p><a href="#v8_serialization_api">Serialization API</a></p> <ul> <li><a href="#v8_v8_serialize_value">v8.serialize(value)</a></li> <li><a href="#v8_v8_deserialize_buffer">v8.deserialize(buffer)</a></li> <li> <p><a href="#v8_class_v8_serializer">class: v8.Serializer</a></p> <ul> <li><a href="#v8_new_serializer">new Serializer()</a></li> <li><a href="#v8_serializer_writeheader">serializer.writeHeader()</a></li> <li><a href="#v8_serializer_writevalue_value">serializer.writeValue(value)</a></li> <li><a href="#v8_serializer_releasebuffer">serializer.releaseBuffer()</a></li> <li><a href="#v8_serializer_transferarraybuffer_id_arraybuffer">serializer.transferArrayBuffer(id, arrayBuffer)</a></li> <li><a href="#v8_serializer_writeuint32_value">serializer.writeUint32(value)</a></li> <li><a href="#v8_serializer_writeuint64_hi_lo">serializer.writeUint64(hi, lo)</a></li> <li><a href="#v8_serializer_writedouble_value">serializer.writeDouble(value)</a></li> <li><a href="#v8_serializer_writerawbytes_buffer">serializer.writeRawBytes(buffer)</a></li> <li><a href="#v8_serializer_writehostobject_object">serializer._writeHostObject(object)</a></li> <li><a href="#v8_serializer_getdatacloneerror_message">serializer._getDataCloneError(message)</a></li> <li><a href="#v8_serializer_getsharedarraybufferid_sharedarraybuffer">serializer._getSharedArrayBufferId(sharedArrayBuffer)</a></li> <li><a href="#v8_serializer_settreatarraybufferviewsashostobjects_flag">serializer._setTreatArrayBufferViewsAsHostObjects(flag)</a></li> </ul> </li> <li> <p><a href="#v8_class_v8_deserializer">class: v8.Deserializer</a></p> <ul> <li><a href="#v8_new_deserializer_buffer">new Deserializer(buffer)</a></li> <li><a href="#v8_deserializer_readheader">deserializer.readHeader()</a></li> <li><a href="#v8_deserializer_readvalue">deserializer.readValue()</a></li> <li><a href="#v8_deserializer_transferarraybuffer_id_arraybuffer">deserializer.transferArrayBuffer(id, arrayBuffer)</a></li> <li><a href="#v8_deserializer_getwireformatversion">deserializer.getWireFormatVersion()</a></li> <li><a href="#v8_deserializer_readuint32">deserializer.readUint32()</a></li> <li><a href="#v8_deserializer_readuint64">deserializer.readUint64()</a></li> <li><a href="#v8_deserializer_readdouble">deserializer.readDouble()</a></li> <li><a href="#v8_deserializer_readrawbytes_length">deserializer.readRawBytes(length)</a></li> <li><a href="#v8_deserializer_readhostobject">deserializer._readHostObject()</a></li> </ul> </li> <li><a href="#v8_class_v8_defaultserializer">class: v8.DefaultSerializer</a></li> <li><a href="#v8_class_v8_defaultdeserializer">class: v8.DefaultDeserializer</a></li> </ul> </li> </ul> </li> </ul> </div> <div id="apicontent"> <h1>V8<span><a class="mark" href="#v8_v8" id="v8_v8">#</a></span></h1> <p>The <code>v8</code> module exposes APIs that are specific to the version of <a href="https://developers.google.com/v8/">V8</a> built into the Node.js binary. It can be accessed using:</p> <pre><code class="language-js">const v8 = require('v8'); </code></pre> <p>The APIs and implementation are subject to change at any time.</p> <h2>v8.cachedDataVersionTag()<span><a class="mark" href="#v8_v8_cacheddataversiontag" id="v8_v8_cacheddataversiontag">#</a></span></h2> <div class="api_metadata"> <span>Added in: v8.0.0</span> </div> <ul> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><integer></a></li> </ul> <p>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 <a href="https://nodejs.org/api/vm.html#vm_constructor_new_vm_script_code_options"><code>vm.Script</code></a> <code>cachedData</code> buffer is compatible with this instance of V8.</p> <h2>v8.getHeapSpaceStatistics()<a class="srclink" href="https://github.com/nodejs/node/blob/3a2e75d9a5c31d20e429d505b82dd182e33f459a/lib/v8.js#L162">[src]</a><span><a class="mark" href="#v8_v8_getheapspacestatistics" id="v8_v8_getheapspacestatistics">#</a></span></h2> <div class="api_metadata"> <details class="changelog"><summary>History</summary> <table> <tbody><tr><th>Version</th><th>Changes</th></tr> <tr><td>v7.5.0</td> <td><p>Support values exceeding the 32-bit unsigned integer range.</p></td></tr> <tr><td>v6.0.0</td> <td><p><span>Added in: v6.0.0</span></p></td></tr> </tbody></table> </details> </div> <ul> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object[]></a></li> </ul> <p>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 <a href="https://v8docs.nodesource.com/node-10.6/d5/dda/classv8_1_1_isolate.html#ac673576f24fdc7a33378f8f57e1d13a4"><code>GetHeapSpaceStatistics</code></a> function and may change from one V8 version to the next.</p> <p>The value returned is an array of objects containing the following properties:</p> <ul> <li><code>space_name</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> <li><code>space_size</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> <li><code>space_used_size</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> <li><code>space_available_size</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> <li><code>physical_space_size</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <pre><code class="language-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 } ] </code></pre> <h2>v8.getHeapSnapshot()<a class="srclink" href="https://github.com/nodejs/node/blob/3a2e75d9a5c31d20e429d505b82dd182e33f459a/lib/v8.js#L76">[src]</a><span><a class="mark" href="#v8_v8_getheapsnapshot" id="v8_v8_getheapsnapshot">#</a></span></h2> <div class="api_metadata"> <span>Added in: v11.13.0</span> </div> <ul> <li>Returns: <a href="https://nodejs.org/api/stream.html#stream_class_stream_readable" class="type"><stream.Readable></a> A Readable Stream containing the V8 heap snapshot</li> </ul> <p>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.</p> <pre><code class="language-js">const stream = v8.getHeapSnapshot(); stream.pipe(process.stdout); </code></pre> <h2>v8.getHeapStatistics()<a class="srclink" href="https://github.com/nodejs/node/blob/3a2e75d9a5c31d20e429d505b82dd182e33f459a/lib/v8.js#L142">[src]</a><span><a class="mark" href="#v8_v8_getheapstatistics" id="v8_v8_getheapstatistics">#</a></span></h2> <div class="api_metadata"> <details class="changelog"><summary>History</summary> <table> <tbody><tr><th>Version</th><th>Changes</th></tr> <tr><td>v7.5.0</td> <td><p>Support values exceeding the 32-bit unsigned integer range.</p></td></tr> <tr><td>v7.2.0</td> <td><p>Added <code>malloced_memory</code>, <code>peak_malloced_memory</code>, and <code>does_zap_garbage</code>.</p></td></tr> <tr><td>v1.0.0</td> <td><p><span>Added in: v1.0.0</span></p></td></tr> </tbody></table> </details> </div> <ul> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li> </ul> <p>Returns an object with the following properties:</p> <ul> <li><code>total_heap_size</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> <li><code>total_heap_size_executable</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> <li><code>total_physical_size</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> <li><code>total_available_size</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> <li><code>used_heap_size</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> <li><code>heap_size_limit</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> <li><code>malloced_memory</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> <li><code>peak_malloced_memory</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> <li><code>does_zap_garbage</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> <li><code>number_of_native_contexts</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> <li><code>number_of_detached_contexts</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p><code>does_zap_garbage</code> is a 0/1 boolean, which signifies whether the <code>--zap_code_space</code> 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.</p> <p><code>number_of_native_contexts</code> 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.</p> <p><code>number_of_detached_contexts</code> 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.</p>  <pre><code class="language-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 } </code></pre> <h2>v8.getHeapCodeStatistics()<a class="srclink" href="https://github.com/nodejs/node/blob/3a2e75d9a5c31d20e429d505b82dd182e33f459a/lib/v8.js#L181">[src]</a><span><a class="mark" href="#v8_v8_getheapcodestatistics" id="v8_v8_getheapcodestatistics">#</a></span></h2> <div class="api_metadata"> <span>Added in: v12.8.0</span> </div> <ul> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li> </ul> <p>Returns an object with the following properties:</p> <ul> <li><code>code_and_metadata_size</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> <li><code>bytecode_and_metadata_size</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> <li><code>external_script_source_size</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul>  <pre><code class="language-js">{ code_and_metadata_size: 212208, bytecode_and_metadata_size: 161368, external_script_source_size: 1410794 } </code></pre> <h2>v8.setFlagsFromString(flags)<a class="srclink" href="https://github.com/nodejs/node/blob/3a2e75d9a5c31d20e429d505b82dd182e33f459a/lib/v8.js#L137">[src]</a><span><a class="mark" href="#v8_v8_setflagsfromstring_flags" id="v8_v8_setflagsfromstring_flags">#</a></span></h2> <div class="api_metadata"> <span>Added in: v1.0.0</span> </div> <ul> <li><code>flags</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> </ul> <p>The <code>v8.setFlagsFromString()</code> 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.</p> <p>The V8 options available for a version of Node.js may be determined by running <code>node --v8-options</code>.</p> <p>Usage:</p> <pre><code class="language-js">// Print GC events to stdout for one minute. const v8 = require('v8'); v8.setFlagsFromString('--trace_gc'); setTimeout(() => { v8.setFlagsFromString('--notrace_gc'); }, 60e3); </code></pre> <h2>v8.writeHeapSnapshot([filename])<a class="srclink" href="https://github.com/nodejs/node/blob/3a2e75d9a5c31d20e429d505b82dd182e33f459a/lib/v8.js#L43">[src]</a><span><a class="mark" href="#v8_v8_writeheapsnapshot_filename" id="v8_v8_writeheapsnapshot_filename">#</a></span></h2> <div class="api_metadata"> <span>Added in: v11.13.0</span> </div> <ul> <li><code>filename</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> The file path where the V8 heap snapshot is to be saved. If not specified, a file name with the pattern <code>'Heap-${yyyymmdd}-${hhmmss}-${pid}-${thread_id}.heapsnapshot'</code> will be generated, where <code>{pid}</code> will be the PID of the Node.js process, <code>{thread_id}</code> will be <code>0</code> when <code>writeHeapSnapshot()</code> is called from the main Node.js thread or the id of a worker thread.</li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> The filename where the snapshot was saved.</li> </ul> <p>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.</p> <p>A heap snapshot is specific to a single V8 isolate. When using <a href="https://nodejs.org/api/worker_threads.html">Worker Threads</a>, a heap snapshot generated from the main thread will not contain any information about the workers, and vice versa.</p> <pre><code class="language-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()); } }); } </code></pre> <h2>Serialization API<span><a class="mark" href="#v8_serialization_api" id="v8_serialization_api">#</a></span></h2> <p></p><div class="api_stability api_stability_1"><a href="https://nodejs.org/api/documentation.html#documentation_stability_index">Stability: 1</a> - Experimental</div><p></p> <p>The serialization API provides means of serializing JavaScript values in a way that is compatible with the <a href="https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API/Structured_clone_algorithm">HTML structured clone algorithm</a>. The format is backward-compatible (i.e. safe to store to disk).</p> <p>This API is under development, and changes (including incompatible changes to the API or wire format) may occur until this warning is removed.</p> <h3>v8.serialize(value)<a class="srclink" href="https://github.com/nodejs/node/blob/3a2e75d9a5c31d20e429d505b82dd182e33f459a/lib/v8.js#L280">[src]</a><span><a class="mark" href="#v8_v8_serialize_value" id="v8_v8_serialize_value">#</a></span></h3> <div class="api_metadata"> <span>Added in: v8.0.0</span> </div> <ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://nodejs.org/api/buffer.html#buffer_class_buffer" class="type"><Buffer></a></li> </ul> <p>Uses a <a href="#v8_class_v8_defaultserializer"><code>DefaultSerializer</code></a> to serialize <code>value</code> into a buffer.</p> <h3>v8.deserialize(buffer)<a class="srclink" href="https://github.com/nodejs/node/blob/3a2e75d9a5c31d20e429d505b82dd182e33f459a/lib/v8.js#L287">[src]</a><span><a class="mark" href="#v8_v8_deserialize_buffer" id="v8_v8_deserialize_buffer">#</a></span></h3> <div class="api_metadata"> <span>Added in: v8.0.0</span> </div> <ul> <li><code>buffer</code> <a href="https://nodejs.org/api/buffer.html#buffer_class_buffer" class="type"><Buffer></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray" class="type"><TypedArray></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView" class="type"><DataView></a> A buffer returned by <a href="#v8_v8_serialize_value"><code>serialize()</code></a>.</li> </ul> <p>Uses a <a href="#v8_class_v8_defaultdeserializer"><code>DefaultDeserializer</code></a> with default options to read a JS value from a buffer.</p> <h3>class: v8.Serializer<span><a class="mark" href="#v8_class_v8_serializer" id="v8_class_v8_serializer">#</a></span></h3> <div class="api_metadata"> <span>Added in: v8.0.0</span> </div> <h4>new Serializer()<span><a class="mark" href="#v8_new_serializer" id="v8_new_serializer">#</a></span></h4> <p>Creates a new <code>Serializer</code> object.</p> <h4>serializer.writeHeader()<span><a class="mark" href="#v8_serializer_writeheader" id="v8_serializer_writeheader">#</a></span></h4> <p>Writes out a header, which includes the serialization format version.</p> <h4>serializer.writeValue(value)<span><a class="mark" href="#v8_serializer_writevalue_value" id="v8_serializer_writevalue_value">#</a></span></h4> <ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> </ul> <p>Serializes a JavaScript value and adds the serialized representation to the internal buffer.</p> <p>This throws an error if <code>value</code> cannot be serialized.</p> <h4>serializer.releaseBuffer()<span><a class="mark" href="#v8_serializer_releasebuffer" id="v8_serializer_releasebuffer">#</a></span></h4> <ul> <li>Returns: <a href="https://nodejs.org/api/buffer.html#buffer_class_buffer" class="type"><Buffer></a></li> </ul> <p>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.</p> <h4>serializer.transferArrayBuffer(id, arrayBuffer)<span><a class="mark" href="#v8_serializer_transferarraybuffer_id_arraybuffer" id="v8_serializer_transferarraybuffer_id_arraybuffer">#</a></span></h4> <ul> <li><code>id</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><integer></a> A 32-bit unsigned integer.</li> <li><code>arrayBuffer</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer" class="type"><ArrayBuffer></a> An <code>ArrayBuffer</code> instance.</li> </ul> <p>Marks an <code>ArrayBuffer</code> as having its contents transferred out of band. Pass the corresponding <code>ArrayBuffer</code> in the deserializing context to <a href="#v8_deserializer_transferarraybuffer_id_arraybuffer"><code>deserializer.transferArrayBuffer()</code></a>.</p> <h4>serializer.writeUint32(value)<span><a class="mark" href="#v8_serializer_writeuint32_value" id="v8_serializer_writeuint32_value">#</a></span></h4> <ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><integer></a></li> </ul> <p>Write a raw 32-bit unsigned integer. For use inside of a custom <a href="#v8_serializer_writehostobject_object"><code>serializer._writeHostObject()</code></a>.</p> <h4>serializer.writeUint64(hi, lo)<span><a class="mark" href="#v8_serializer_writeuint64_hi_lo" id="v8_serializer_writeuint64_hi_lo">#</a></span></h4> <ul> <li><code>hi</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><integer></a></li> <li><code>lo</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><integer></a></li> </ul> <p>Write a raw 64-bit unsigned integer, split into high and low 32-bit parts. For use inside of a custom <a href="#v8_serializer_writehostobject_object"><code>serializer._writeHostObject()</code></a>.</p> <h4>serializer.writeDouble(value)<span><a class="mark" href="#v8_serializer_writedouble_value" id="v8_serializer_writedouble_value">#</a></span></h4> <ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>Write a JS <code>number</code> value. For use inside of a custom <a href="#v8_serializer_writehostobject_object"><code>serializer._writeHostObject()</code></a>.</p> <h4>serializer.writeRawBytes(buffer)<span><a class="mark" href="#v8_serializer_writerawbytes_buffer" id="v8_serializer_writerawbytes_buffer">#</a></span></h4> <ul> <li><code>buffer</code> <a href="https://nodejs.org/api/buffer.html#buffer_class_buffer" class="type"><Buffer></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray" class="type"><TypedArray></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView" class="type"><DataView></a></li> </ul> <p>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 <a href="#v8_serializer_writehostobject_object"><code>serializer._writeHostObject()</code></a>.</p> <h4>serializer._writeHostObject(object)<span><a class="mark" href="#v8_serializer_writehostobject_object" id="v8_serializer_writehostobject_object">#</a></span></h4> <ul> <li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li> </ul> <p>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 <code>object</code>, a suitable exception should be thrown.</p> <p>This method is not present on the <code>Serializer</code> class itself but can be provided by subclasses.</p> <h4>serializer._getDataCloneError(message)<span><a class="mark" href="#v8_serializer_getdatacloneerror_message" id="v8_serializer_getdatacloneerror_message">#</a></span></h4> <ul> <li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> </ul> <p>This method is called to generate error objects that will be thrown when an object can not be cloned.</p> <p>This method defaults to the <a href="https://nodejs.org/api/errors.html#errors_class_error"><code>Error</code></a> constructor and can be overridden on subclasses.</p> <h4>serializer._getSharedArrayBufferId(sharedArrayBuffer)<span><a class="mark" href="#v8_serializer_getsharedarraybufferid_sharedarraybuffer" id="v8_serializer_getsharedarraybufferid_sharedarraybuffer">#</a></span></h4> <ul> <li><code>sharedArrayBuffer</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer" class="type"><SharedArrayBuffer></a></li> </ul> <p>This method is called when the serializer is going to serialize a <code>SharedArrayBuffer</code> object. It must return an unsigned 32-bit integer ID for the object, using the same ID if this <code>SharedArrayBuffer</code> has already been serialized. When deserializing, this ID will be passed to <a href="#v8_deserializer_transferarraybuffer_id_arraybuffer"><code>deserializer.transferArrayBuffer()</code></a>.</p> <p>If the object cannot be serialized, an exception should be thrown.</p> <p>This method is not present on the <code>Serializer</code> class itself but can be provided by subclasses.</p> <h4>serializer._setTreatArrayBufferViewsAsHostObjects(flag)<span><a class="mark" href="#v8_serializer_settreatarraybufferviewsashostobjects_flag" id="v8_serializer_settreatarraybufferviewsashostobjects_flag">#</a></span></h4> <ul> <li><code>flag</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> <strong>Default:</strong> <code>false</code></li> </ul> <p>Indicate whether to treat <code>TypedArray</code> and <code>DataView</code> objects as host objects, i.e. pass them to <a href="#v8_serializer_writehostobject_object"><code>serializer._writeHostObject()</code></a>.</p> <h3>class: v8.Deserializer<span><a class="mark" href="#v8_class_v8_deserializer" id="v8_class_v8_deseri