Returns an object containing commonly used constants for VM operations.
Node.js module
vm
The 'node:vm'
module provides APIs to compile and run code within V8 virtual machines contexts. It includes Script
, createContext
, and runInContext
functions.
Use it to sandbox code execution, evaluate untrusted scripts safely, or preload global variables in isolated contexts.
Works in Bun
Core script execution functionality works. Experimental VM ES Modules (`vm.Module`, etc.) and the `importModuleDynamically` hook are not implemented. Several options like `timeout`, `breakOnSigint`, and `cachedData` are also not yet implemented.
namespace constants
This constant, when used as the
contextObject
argument in vm APIs, instructs Node.js to create a context without wrapping its global object with another object in a Node.js-specific manner. As a result, theglobalThis
value inside the new context would behave more closely to an ordinary one.When
vm.constants.DONT_CONTEXTIFY
is used as thecontextObject
argument to createContext, the returned object is a proxy-like object to the global object in the newly created context with fewer Node.js-specific quirks. It is reference equal to theglobalThis
value in the new context, can be modified from outside the context, and can be used to access built-ins in the new context directly.A constant that can be used as the
importModuleDynamically
option tovm.Script
andvm.compileFunction()
so that Node.js uses the default ESM loader from the main context to load the requested module.For detailed information, see Support of dynamic
import()
in compilation APIs.
class Module
This feature is only available with the
--experimental-vm-modules
command flag enabled.The
vm.Module
class provides a low-level interface for using ECMAScript modules in VM contexts. It is the counterpart of thevm.Script
class that closely mirrors Module Record s as defined in the ECMAScript specification.Unlike
vm.Script
however, everyvm.Module
object is bound to a context from its creation. Operations onvm.Module
objects are intrinsically asynchronous, in contrast with the synchronous nature ofvm.Script
objects. The use of 'async' functions can help with manipulatingvm.Module
objects.Using a
vm.Module
object requires three distinct steps: creation/parsing, linking, and evaluation. These three steps are illustrated in the following example.This implementation lies at a lower level than the
ECMAScript Module loader
. There is also no way to interact with the Loader yet, though support is planned.import vm from 'node:vm'; const contextifiedObject = vm.createContext({ secret: 42, print: console.log, }); // Step 1 // // Create a Module by constructing a new `vm.SourceTextModule` object. This // parses the provided source text, throwing a `SyntaxError` if anything goes // wrong. By default, a Module is created in the top context. But here, we // specify `contextifiedObject` as the context this Module belongs to. // // Here, we attempt to obtain the default export from the module "foo", and // put it into local binding "secret". const bar = new vm.SourceTextModule(` import s from 'foo'; s; print(s); `, { context: contextifiedObject }); // Step 2 // // "Link" the imported dependencies of this Module to it. // // The provided linking callback (the "linker") accepts two arguments: the // parent module (`bar` in this case) and the string that is the specifier of // the imported module. The callback is expected to return a Module that // corresponds to the provided specifier, with certain requirements documented // in `module.link()`. // // If linking has not started for the returned Module, the same linker // callback will be called on the returned Module. // // Even top-level Modules without dependencies must be explicitly linked. The // callback provided would never be called, however. // // The link() method returns a Promise that will be resolved when all the // Promises returned by the linker resolve. // // Note: This is a contrived example in that the linker function creates a new // "foo" module every time it is called. In a full-fledged module system, a // cache would probably be used to avoid duplicated modules. async function linker(specifier, referencingModule) { if (specifier === 'foo') { return new vm.SourceTextModule(` // The "secret" variable refers to the global variable we added to // "contextifiedObject" when creating the context. export default secret; `, { context: referencingModule.context }); // Using `contextifiedObject` instead of `referencingModule.context` // here would work as well. } throw new Error(`Unable to resolve dependency: ${specifier}`); } await bar.link(linker); // Step 3 // // Evaluate the Module. The evaluate() method returns a promise which will // resolve after the module has finished evaluating. // Prints 42. await bar.evaluate();
- dependencySpecifiers: readonly string[]
The specifiers of all dependencies of this module. The returned array is frozen to disallow any changes to it.
Corresponds to the
[[RequestedModules]]
field of Cyclic Module Record s in the ECMAScript specification. - error: any
If the
module.status
is'errored'
, this property contains the exception thrown by the module during evaluation. If the status is anything else, accessing this property will result in a thrown exception.The value
undefined
cannot be used for cases where there is not a thrown exception due to possible ambiguity withthrow undefined;
.Corresponds to the
[[EvaluationError]]
field of Cyclic Module Record s in the ECMAScript specification. - namespace: Object
The namespace object of the module. This is only available after linking (
module.link()
) has completed.Corresponds to the GetModuleNamespace abstract operation in the ECMAScript specification.
- status: ModuleStatus
The current status of the module. Will be one of:
'unlinked'
:module.link()
has not yet been called.'linking'
:module.link()
has been called, but not all Promises returned by the linker function have been resolved yet.'linked'
: The module has been linked successfully, and all of its dependencies are linked, butmodule.evaluate()
has not yet been called.'evaluating'
: The module is being evaluated through amodule.evaluate()
on itself or a parent module.'evaluated'
: The module has been successfully evaluated.'errored'
: The module has been evaluated, but an exception was thrown.
Other than
'errored'
, this status string corresponds to the specification's Cyclic Module Record's[[Status]]
field.'errored'
corresponds to'evaluated'
in the specification, but with[[EvaluationError]]
set to a value that is notundefined
. - ): Promise<void>;
Evaluate the module.
This must be called after the module has been linked; otherwise it will reject. It could be called also when the module has already been evaluated, in which case it will either do nothing if the initial evaluation ended in success (
module.status
is'evaluated'
) or it will re-throw the exception that the initial evaluation resulted in (module.status
is'errored'
).This method cannot be called while the module is being evaluated (
module.status
is'evaluating'
).Corresponds to the Evaluate() concrete method field of Cyclic Module Record s in the ECMAScript specification.
@returnsFulfills with
undefined
upon success. - link(): Promise<void>;
Link module dependencies. This method must be called before evaluation, and can only be called once per module.
The function is expected to return a
Module
object or aPromise
that eventually resolves to aModule
object. The returnedModule
must satisfy the following two invariants:- It must belong to the same context as the parent
Module
. - Its
status
must not be'errored'
.
If the returned
Module
'sstatus
is'unlinked'
, this method will be recursively called on the returnedModule
with the same providedlinker
function.link()
returns aPromise
that will either get resolved when all linking instances resolve to a validModule
, or rejected if the linker function either throws an exception or returns an invalidModule
.The linker function roughly corresponds to the implementation-defined HostResolveImportedModule abstract operation in the ECMAScript specification, with a few key differences:
- The linker function is allowed to be asynchronous while HostResolveImportedModule is synchronous.
The actual HostResolveImportedModule implementation used during module linking is one that returns the modules linked during linking. Since at that point all modules would have been fully linked already, the HostResolveImportedModule implementation is fully synchronous per specification.
Corresponds to the Link() concrete method field of Cyclic Module Record s in the ECMAScript specification.
- It must belong to the same context as the parent
class Script
Instances of the
vm.Script
class contain precompiled scripts that can be executed in specific contexts.- cachedDataRejected?: boolean
When
cachedData
is supplied to create thevm.Script
, this value will be set to eithertrue
orfalse
depending on acceptance of the data by V8. Otherwise the value isundefined
. - sourceMapURL?: string
When the script is compiled from a source that contains a source map magic comment, this property will be set to the URL of the source map.
import vm from 'node:vm'; const script = new vm.Script(` function myFunc() {} //# sourceMappingURL=sourcemap.json `); console.log(script.sourceMapURL); // Prints: sourcemap.json
Creates a code cache that can be used with the
Script
constructor'scachedData
option. Returns aBuffer
. This method may be called at any time and any number of times.The code cache of the
Script
doesn't contain any JavaScript observable states. The code cache is safe to be saved along side the script source and used to construct newScript
instances multiple times.Functions in the
Script
source can be marked as lazily compiled and they are not compiled at construction of theScript
. These functions are going to be compiled when they are invoked the first time. The code cache serializes the metadata that V8 currently knows about theScript
that it can use to speed up future compilations.const script = new vm.Script(` function add(a, b) { return a + b; } const x = add(1, 2); `); const cacheWithoutAdd = script.createCachedData(); // In `cacheWithoutAdd` the function `add()` is marked for full compilation // upon invocation. script.runInThisContext(); const cacheWithAdd = script.createCachedData(); // `cacheWithAdd` contains fully compiled function `add()`.
- ): any;
Runs the compiled code contained by the
vm.Script
object within the givencontextifiedObject
and returns the result. Running code does not have access to local scope.The following example compiles code that increments a global variable, sets the value of another global variable, then execute the code multiple times. The globals are contained in the
context
object.import vm from 'node:vm'; const context = { animal: 'cat', count: 2, }; const script = new vm.Script('count += 1; name = "kitty";'); vm.createContext(context); for (let i = 0; i < 10; ++i) { script.runInContext(context); } console.log(context); // Prints: { animal: 'cat', count: 12, name: 'kitty' }
Using the
timeout
orbreakOnSigint
options will result in new event loops and corresponding threads being started, which have a non-zero performance overhead.@param contextifiedObjectA
contextified
object as returned by thevm.createContext()
method.@returnsthe result of the very last statement executed in the script.
- ): any;
This method is a shortcut to
script.runInContext(vm.createContext(options), options)
. It does several things at once:- Creates a new context.
- If
contextObject
is an object, contextifies it with the new context. IfcontextObject
is undefined, creates a new object and contextifies it. IfcontextObject
isvm.constants.DONT_CONTEXTIFY
, don't contextify anything. - Runs the compiled code contained by the
vm.Script
object within the created context. The code does not have access to the scope in which this method is called. - Returns the result.
The following example compiles code that sets a global variable, then executes the code multiple times in different contexts. The globals are set on and contained within each individual
context
.const vm = require('node:vm'); const script = new vm.Script('globalVar = "set"'); const contexts = [{}, {}, {}]; contexts.forEach((context) => { script.runInNewContext(context); }); console.log(contexts); // Prints: [{ globalVar: 'set' }, { globalVar: 'set' }, { globalVar: 'set' }] // This would throw if the context is created from a contextified object. // vm.constants.DONT_CONTEXTIFY allows creating contexts with ordinary // global objects that can be frozen. const freezeScript = new vm.Script('Object.freeze(globalThis); globalThis;'); const frozenContext = freezeScript.runInNewContext(vm.constants.DONT_CONTEXTIFY);
@param contextObjectEither
vm.constants.DONT_CONTEXTIFY
or an object that will be contextified. Ifundefined
, an empty contextified object will be created for backwards compatibility.@returnsthe result of the very last statement executed in the script.
- ): any;
Runs the compiled code contained by the
vm.Script
within the context of the currentglobal
object. Running code does not have access to local scope, but does have access to the currentglobal
object.The following example compiles code that increments a
global
variable then executes that code multiple times:import vm from 'node:vm'; global.globalVar = 0; const script = new vm.Script('globalVar += 1', { filename: 'myfile.vm' }); for (let i = 0; i < 1000; ++i) { script.runInThisContext(); } console.log(globalVar); // 1000
@returnsthe result of the very last statement executed in the script.
class SourceTextModule
This feature is only available with the
--experimental-vm-modules
command flag enabled.The
vm.SourceTextModule
class provides the Source Text Module Record as defined in the ECMAScript specification.- dependencySpecifiers: readonly string[]
The specifiers of all dependencies of this module. The returned array is frozen to disallow any changes to it.
Corresponds to the
[[RequestedModules]]
field of Cyclic Module Record s in the ECMAScript specification. - error: any
If the
module.status
is'errored'
, this property contains the exception thrown by the module during evaluation. If the status is anything else, accessing this property will result in a thrown exception.The value
undefined
cannot be used for cases where there is not a thrown exception due to possible ambiguity withthrow undefined;
.Corresponds to the
[[EvaluationError]]
field of Cyclic Module Record s in the ECMAScript specification. - namespace: Object
The namespace object of the module. This is only available after linking (
module.link()
) has completed.Corresponds to the GetModuleNamespace abstract operation in the ECMAScript specification.
- status: ModuleStatus
The current status of the module. Will be one of:
'unlinked'
:module.link()
has not yet been called.'linking'
:module.link()
has been called, but not all Promises returned by the linker function have been resolved yet.'linked'
: The module has been linked successfully, and all of its dependencies are linked, butmodule.evaluate()
has not yet been called.'evaluating'
: The module is being evaluated through amodule.evaluate()
on itself or a parent module.'evaluated'
: The module has been successfully evaluated.'errored'
: The module has been evaluated, but an exception was thrown.
Other than
'errored'
, this status string corresponds to the specification's Cyclic Module Record's[[Status]]
field.'errored'
corresponds to'evaluated'
in the specification, but with[[EvaluationError]]
set to a value that is notundefined
. - ): Promise<void>;
Evaluate the module.
This must be called after the module has been linked; otherwise it will reject. It could be called also when the module has already been evaluated, in which case it will either do nothing if the initial evaluation ended in success (
module.status
is'evaluated'
) or it will re-throw the exception that the initial evaluation resulted in (module.status
is'errored'
).This method cannot be called while the module is being evaluated (
module.status
is'evaluating'
).Corresponds to the Evaluate() concrete method field of Cyclic Module Record s in the ECMAScript specification.
@returnsFulfills with
undefined
upon success. - link(): Promise<void>;
Link module dependencies. This method must be called before evaluation, and can only be called once per module.
The function is expected to return a
Module
object or aPromise
that eventually resolves to aModule
object. The returnedModule
must satisfy the following two invariants:- It must belong to the same context as the parent
Module
. - Its
status
must not be'errored'
.
If the returned
Module
'sstatus
is'unlinked'
, this method will be recursively called on the returnedModule
with the same providedlinker
function.link()
returns aPromise
that will either get resolved when all linking instances resolve to a validModule
, or rejected if the linker function either throws an exception or returns an invalidModule
.The linker function roughly corresponds to the implementation-defined HostResolveImportedModule abstract operation in the ECMAScript specification, with a few key differences:
- The linker function is allowed to be asynchronous while HostResolveImportedModule is synchronous.
The actual HostResolveImportedModule implementation used during module linking is one that returns the modules linked during linking. Since at that point all modules would have been fully linked already, the HostResolveImportedModule implementation is fully synchronous per specification.
Corresponds to the Link() concrete method field of Cyclic Module Record s in the ECMAScript specification.
- It must belong to the same context as the parent
class SyntheticModule
This feature is only available with the
--experimental-vm-modules
command flag enabled.The
vm.SyntheticModule
class provides the Synthetic Module Record as defined in the WebIDL specification. The purpose of synthetic modules is to provide a generic interface for exposing non-JavaScript sources to ECMAScript module graphs.import vm from 'node:vm'; const source = '{ "a": 1 }'; const module = new vm.SyntheticModule(['default'], function() { const obj = JSON.parse(source); this.setExport('default', obj); }); // Use `module` in linking...
- dependencySpecifiers: readonly string[]
The specifiers of all dependencies of this module. The returned array is frozen to disallow any changes to it.
Corresponds to the
[[RequestedModules]]
field of Cyclic Module Record s in the ECMAScript specification. - error: any
If the
module.status
is'errored'
, this property contains the exception thrown by the module during evaluation. If the status is anything else, accessing this property will result in a thrown exception.The value
undefined
cannot be used for cases where there is not a thrown exception due to possible ambiguity withthrow undefined;
.Corresponds to the
[[EvaluationError]]
field of Cyclic Module Record s in the ECMAScript specification. - namespace: Object
The namespace object of the module. This is only available after linking (
module.link()
) has completed.Corresponds to the GetModuleNamespace abstract operation in the ECMAScript specification.
- status: ModuleStatus
The current status of the module. Will be one of:
'unlinked'
:module.link()
has not yet been called.'linking'
:module.link()
has been called, but not all Promises returned by the linker function have been resolved yet.'linked'
: The module has been linked successfully, and all of its dependencies are linked, butmodule.evaluate()
has not yet been called.'evaluating'
: The module is being evaluated through amodule.evaluate()
on itself or a parent module.'evaluated'
: The module has been successfully evaluated.'errored'
: The module has been evaluated, but an exception was thrown.
Other than
'errored'
, this status string corresponds to the specification's Cyclic Module Record's[[Status]]
field.'errored'
corresponds to'evaluated'
in the specification, but with[[EvaluationError]]
set to a value that is notundefined
. - ): Promise<void>;
Evaluate the module.
This must be called after the module has been linked; otherwise it will reject. It could be called also when the module has already been evaluated, in which case it will either do nothing if the initial evaluation ended in success (
module.status
is'evaluated'
) or it will re-throw the exception that the initial evaluation resulted in (module.status
is'errored'
).This method cannot be called while the module is being evaluated (
module.status
is'evaluating'
).Corresponds to the Evaluate() concrete method field of Cyclic Module Record s in the ECMAScript specification.
@returnsFulfills with
undefined
upon success. - link(): Promise<void>;
Link module dependencies. This method must be called before evaluation, and can only be called once per module.
The function is expected to return a
Module
object or aPromise
that eventually resolves to aModule
object. The returnedModule
must satisfy the following two invariants:- It must belong to the same context as the parent
Module
. - Its
status
must not be'errored'
.
If the returned
Module
'sstatus
is'unlinked'
, this method will be recursively called on the returnedModule
with the same providedlinker
function.link()
returns aPromise
that will either get resolved when all linking instances resolve to a validModule
, or rejected if the linker function either throws an exception or returns an invalidModule
.The linker function roughly corresponds to the implementation-defined HostResolveImportedModule abstract operation in the ECMAScript specification, with a few key differences:
- The linker function is allowed to be asynchronous while HostResolveImportedModule is synchronous.
The actual HostResolveImportedModule implementation used during module linking is one that returns the modules linked during linking. Since at that point all modules would have been fully linked already, the HostResolveImportedModule implementation is fully synchronous per specification.
Corresponds to the Link() concrete method field of Cyclic Module Record s in the ECMAScript specification.
- It must belong to the same context as the parent
- name: string,value: any): void;
This method is used after the module is linked to set the values of exports. If it is called before the module is linked, an
ERR_VM_MODULE_STATUS
error will be thrown.import vm from 'node:vm'; const m = new vm.SyntheticModule(['x'], () => { m.setExport('x', 1); }); await m.link(() => {}); await m.evaluate(); assert.strictEqual(m.namespace.x, 1);
@param nameName of the export to set.
@param valueThe value to set the export to.
- code: string,params?: readonly string[],): Function & { cachedData: Buffer<ArrayBufferLike>; cachedDataProduced: boolean; cachedDataRejected: boolean };
Compiles the given code into the provided context (if no context is supplied, the current context is used), and returns it wrapped inside a function with the given
params
.@param codeThe body of the function to compile.
@param paramsAn array of strings containing all parameters for the function.
If the given
contextObject
is an object, thevm.createContext()
method will prepare that object and return a reference to it so that it can be used in calls to runInContext orscript.runInContext()
. Inside such scripts, the global object will be wrapped by thecontextObject
, retaining all of its existing properties but also having the built-in objects and functions any standard global object has. Outside of scripts run by the vm module, global variables will remain unchanged.const vm = require('node:vm'); global.globalVar = 3; const context = { globalVar: 1 }; vm.createContext(context); vm.runInContext('globalVar *= 2;', context); console.log(context); // Prints: { globalVar: 2 } console.log(global.globalVar); // Prints: 3
If
contextObject
is omitted (or passed explicitly asundefined
), a new, empty contextified object will be returned.When the global object in the newly created context is contextified, it has some quirks compared to ordinary global objects. For example, it cannot be frozen. To create a context without the contextifying quirks, pass
vm.constants.DONT_CONTEXTIFY
as thecontextObject
argument. See the documentation ofvm.constants.DONT_CONTEXTIFY
for details.The
vm.createContext()
method is primarily useful for creating a single context that can be used to run multiple scripts. For instance, if emulating a web browser, the method can be used to create a single context representing a window's global object, then run all<script>
tags together within that context.The provided
name
andorigin
of the context are made visible through the Inspector API.@param contextObjectEither
vm.constants.DONT_CONTEXTIFY
or an object that will be contextified. Ifundefined
, an empty contextified object will be created for backwards compatibility.@returnscontextified object.
Measure the memory known to V8 and used by all contexts known to the current V8 isolate, or the main context.
The format of the object that the returned Promise may resolve with is specific to the V8 engine and may change from one version of V8 to the next.
The returned result is different from the statistics returned by
v8.getHeapSpaceStatistics()
in thatvm.measureMemory()
measure the memory reachable by each V8 specific contexts in the current instance of the V8 engine, while the result ofv8.getHeapSpaceStatistics()
measure the memory occupied by each heap space in the current V8 instance.import vm from 'node:vm'; // Measure the memory used by the main context. vm.measureMemory({ mode: 'summary' }) // This is the same as vm.measureMemory() .then((result) => { // The current format is: // { // total: { // jsMemoryEstimate: 2418479, jsMemoryRange: [ 2418479, 2745799 ] // } // } console.log(result); }); const context = vm.createContext({ a: 1 }); vm.measureMemory({ mode: 'detailed', execution: 'eager' }) .then((result) => { // Reference the context here so that it won't be GC'ed // until the measurement is complete. console.log(context.a); // { // total: { // jsMemoryEstimate: 2574732, // jsMemoryRange: [ 2574732, 2904372 ] // }, // current: { // jsMemoryEstimate: 2438996, // jsMemoryRange: [ 2438996, 2768636 ] // }, // other: [ // { // jsMemoryEstimate: 135736, // jsMemoryRange: [ 135736, 465376 ] // } // ] // } console.log(result); });
- code: string,): any;
The
vm.runInContext()
method compilescode
, runs it within the context of thecontextifiedObject
, then returns the result. Running code does not have access to the local scope. ThecontextifiedObject
object must have been previouslycontextified
using the createContext method.If
options
is a string, then it specifies the filename.The following example compiles and executes different scripts using a single
contextified
object:import vm from 'node:vm'; const contextObject = { globalVar: 1 }; vm.createContext(contextObject); for (let i = 0; i < 10; ++i) { vm.runInContext('globalVar *= 2;', contextObject); } console.log(contextObject); // Prints: { globalVar: 1024 }
@param codeThe JavaScript code to compile and run.
@param contextifiedObjectThe
contextified
object that will be used as theglobal
when thecode
is compiled and run.@returnsthe result of the very last statement executed in the script.
- code: string,): any;
This method is a shortcut to
(new vm.Script(code, options)).runInContext(vm.createContext(options), options)
. Ifoptions
is a string, then it specifies the filename.It does several things at once:
- Creates a new context.
- If
contextObject
is an object, contextifies it with the new context. IfcontextObject
is undefined, creates a new object and contextifies it. IfcontextObject
isvm.constants.DONT_CONTEXTIFY
, don't contextify anything. - Compiles the code as a
vm.Script
- Runs the compield code within the created context. The code does not have access to the scope in which this method is called.
- Returns the result.
The following example compiles and executes code that increments a global variable and sets a new one. These globals are contained in the
contextObject
.const vm = require('node:vm'); const contextObject = { animal: 'cat', count: 2, }; vm.runInNewContext('count += 1; name = "kitty"', contextObject); console.log(contextObject); // Prints: { animal: 'cat', count: 3, name: 'kitty' } // This would throw if the context is created from a contextified object. // vm.constants.DONT_CONTEXTIFY allows creating contexts with ordinary global objects that // can be frozen. const frozenContext = vm.runInNewContext('Object.freeze(globalThis); globalThis;', vm.constants.DONT_CONTEXTIFY);
@param codeThe JavaScript code to compile and run.
@param contextObjectEither
vm.constants.DONT_CONTEXTIFY
or an object that will be contextified. Ifundefined
, an empty contextified object will be created for backwards compatibility.@returnsthe result of the very last statement executed in the script.
- code: string,): any;
vm.runInThisContext()
compilescode
, runs it within the context of the currentglobal
and returns the result. Running code does not have access to local scope, but does have access to the currentglobal
object.If
options
is a string, then it specifies the filename.The following example illustrates using both
vm.runInThisContext()
and the JavaScripteval()
function to run the same code:import vm from 'node:vm'; let localVar = 'initial value'; const vmResult = vm.runInThisContext('localVar = "vm";'); console.log(`vmResult: '${vmResult}', localVar: '${localVar}'`); // Prints: vmResult: 'vm', localVar: 'initial value' const evalResult = eval('localVar = "eval";'); console.log(`evalResult: '${evalResult}', localVar: '${localVar}'`); // Prints: evalResult: 'eval', localVar: 'eval'
Because
vm.runInThisContext()
does not have access to the local scope,localVar
is unchanged. In contrast,eval()
does have access to the local scope, so the valuelocalVar
is changed. In this wayvm.runInThisContext()
is much like an indirecteval()
call, e.g.(0,eval)('code')
.Example: Running an HTTP server within a VM
When using either
script.runInThisContext()
or runInThisContext, the code is executed within the current V8 global context. The code passed to this VM context will have its own isolated scope.In order to run a simple web server using the
node:http
module the code passed to the context must either importnode:http
on its own, or have a reference to thenode:http
module passed to it. For instance:'use strict'; import vm from 'node:vm'; const code = ` ((require) => { const http = require('node:http'); http.createServer((request, response) => { response.writeHead(200, { 'Content-Type': 'text/plain' }); response.end('Hello World\\n'); }).listen(8124); console.log('Server running at http://127.0.0.1:8124/'); })`; vm.runInThisContext(code)(require);
The
require()
in the above case shares the state with the context it is passed from. This may introduce risks when untrusted code is executed, e.g. altering objects in the context in unwanted ways.@param codeThe JavaScript code to compile and run.
@returnsthe result of the very last statement executed in the script.
Type definitions
interface BaseOptions
- columnOffset?: number
Specifies the column number offset that is displayed in stack traces produced by this script.
- lineOffset?: number
Specifies the line number offset that is displayed in stack traces produced by this script.
interface CompileFunctionOptions
- cachedData?: Buffer<ArrayBufferLike>
Provides an optional data with V8's code cache data for the supplied source.
- columnOffset?: number
Specifies the column number offset that is displayed in stack traces produced by this script.
- contextExtensions?: Object[]
An array containing a collection of context extensions (objects wrapping the current scope) to be applied while compiling
- lineOffset?: number
Specifies the line number offset that is displayed in stack traces produced by this script.
interface Context
interface CreateContextOptions
- microtaskMode?: 'afterEvaluate'
If set to
afterEvaluate
, microtasks will be run immediately after the script has run. - origin?: string
Corresponds to the newly created context for display purposes. The origin should be formatted like a
URL
, but with only the scheme, host, and port (if necessary), like the value of theurl.origin
property of a URL object. Most notably, this string should omit the trailing slash, as that denotes a path.
interface MeasureMemoryOptions
interface MemoryMeasurement
interface ModuleEvaluateOptions
interface RunningCodeInNewContextOptions
- breakOnSigint?: boolean
If
true
, the execution will be terminated whenSIGINT
(Ctrl+C) is received. Existing handlers for the event that have been attached viaprocess.on('SIGINT')
will be disabled during script execution, but will continue to work after that. If execution is terminated, anError
will be thrown. - columnOffset?: number
Specifies the column number offset that is displayed in stack traces produced by this script.
- contextOrigin?: string
Origin corresponding to the newly created context for display purposes. The origin should be formatted like a URL, but with only the scheme, host, and port (if necessary), like the value of the
url.origin
property of aURL
object. Most notably, this string should omit the trailing slash, as that denotes a path. - displayErrors?: boolean
When
true
, if anError
occurs while compiling thecode
, the line of code causing the error is attached to the stack trace. - importModuleDynamically?: number | (specifier: string, script: Script, importAttributes: ImportAttributes) => Module | Promise<Module>
- lineOffset?: number
Specifies the line number offset that is displayed in stack traces produced by this script.
- microtaskMode?: 'afterEvaluate'
If set to
afterEvaluate
, microtasks will be run immediately after the script has run. - timeout?: number
Specifies the number of milliseconds to execute code before terminating execution. If execution is terminated, an
Error
will be thrown. This value must be a strictly positive integer.
interface RunningCodeOptions
- breakOnSigint?: boolean
If
true
, the execution will be terminated whenSIGINT
(Ctrl+C) is received. Existing handlers for the event that have been attached viaprocess.on('SIGINT')
will be disabled during script execution, but will continue to work after that. If execution is terminated, anError
will be thrown. - columnOffset?: number
Specifies the column number offset that is displayed in stack traces produced by this script.
- displayErrors?: boolean
When
true
, if anError
occurs while compiling thecode
, the line of code causing the error is attached to the stack trace. - importModuleDynamically?: number | (specifier: string, script: Script, importAttributes: ImportAttributes) => Module | Promise<Module>
- lineOffset?: number
Specifies the line number offset that is displayed in stack traces produced by this script.
- timeout?: number
Specifies the number of milliseconds to execute code before terminating execution. If execution is terminated, an
Error
will be thrown. This value must be a strictly positive integer.
interface RunningScriptInNewContextOptions
- breakOnSigint?: boolean
If
true
, the execution will be terminated whenSIGINT
(Ctrl+C) is received. Existing handlers for the event that have been attached viaprocess.on('SIGINT')
will be disabled during script execution, but will continue to work after that. If execution is terminated, anError
will be thrown. - columnOffset?: number
Specifies the column number offset that is displayed in stack traces produced by this script.
- contextOrigin?: string
Origin corresponding to the newly created context for display purposes. The origin should be formatted like a URL, but with only the scheme, host, and port (if necessary), like the value of the
url.origin
property of aURL
object. Most notably, this string should omit the trailing slash, as that denotes a path. - displayErrors?: boolean
When
true
, if anError
occurs while compiling thecode
, the line of code causing the error is attached to the stack trace. - lineOffset?: number
Specifies the line number offset that is displayed in stack traces produced by this script.
- microtaskMode?: 'afterEvaluate'
If set to
afterEvaluate
, microtasks will be run immediately after the script has run. - timeout?: number
Specifies the number of milliseconds to execute code before terminating execution. If execution is terminated, an
Error
will be thrown. This value must be a strictly positive integer.
interface RunningScriptOptions
- breakOnSigint?: boolean
If
true
, the execution will be terminated whenSIGINT
(Ctrl+C) is received. Existing handlers for the event that have been attached viaprocess.on('SIGINT')
will be disabled during script execution, but will continue to work after that. If execution is terminated, anError
will be thrown. - columnOffset?: number
Specifies the column number offset that is displayed in stack traces produced by this script.
- displayErrors?: boolean
When
true
, if anError
occurs while compiling thecode
, the line of code causing the error is attached to the stack trace. - lineOffset?: number
Specifies the line number offset that is displayed in stack traces produced by this script.
- timeout?: number
Specifies the number of milliseconds to execute code before terminating execution. If execution is terminated, an
Error
will be thrown. This value must be a strictly positive integer.
interface ScriptOptions
- cachedData?: Buffer<ArrayBufferLike> | ArrayBufferView<ArrayBufferLike>
V8's code cache data for the supplied source.
- columnOffset?: number
Specifies the column number offset that is displayed in stack traces produced by this script.
- importModuleDynamically?: number | (specifier: string, script: Script, importAttributes: ImportAttributes) => Module | Promise<Module>
Used to specify how the modules should be loaded during the evaluation of this script when
import()
is called. This option is part of the experimental modules API. We do not recommend using it in a production environment. For detailed information, see Support of dynamicimport()
in compilation APIs. - lineOffset?: number
Specifies the line number offset that is displayed in stack traces produced by this script.
interface SourceTextModuleOptions
- importModuleDynamically?: number | (specifier: string, script: Script, importAttributes: ImportAttributes) => Module | Promise<Module>
- initializeImportMeta?: (meta: ImportMeta, module: SourceTextModule) => void
Called during evaluation of this module to initialize the
import.meta
.
interface SyntheticModuleOptions
- type MeasureMemoryMode = 'summary' | 'detailed'
- type ModuleLinker = (specifier: string, referencingModule: Module, extra: { attributes: ImportAttributes }) => Module | Promise<Module>
- type ModuleStatus = 'unlinked' | 'linking' | 'linked' | 'evaluating' | 'evaluated' | 'errored'