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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

    Returns an object containing commonly used constants for VM operations.

    • const DONT_CONTEXTIFY: number

      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, the globalThis value inside the new context would behave more closely to an ordinary one.

      When vm.constants.DONT_CONTEXTIFY is used as the contextObject 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 the globalThis 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 to vm.Script and vm.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 the vm.Script class that closely mirrors Module Records as defined in the ECMAScript specification.

    Unlike vm.Script however, every vm.Module object is bound to a context from its creation.

    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 rootModule = new vm.SourceTextModule(`
  import s from 'foo';
  s;
  print(s);
`, { context: contextifiedObject });

// Step 2
//
// "Link" the imported dependencies of this Module to it.
//
// Obtain the requested dependencies of a SourceTextModule by
// `sourceTextModule.moduleRequests` and resolve them.
//
// Even top-level Modules without dependencies must be explicitly linked. The
// array passed to `sourceTextModule.linkRequests(modules)` can be
// empty, however.
//
// Note: This is a contrived example in that the resolveAndLinkDependencies
// 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.

const moduleMap = new Map([
  ['root', rootModule],
]);

function resolveAndLinkDependencies(module) {
  const requestedModules = module.moduleRequests.map((request) => {
    // In a full-fledged module system, the resolveAndLinkDependencies would
    // resolve the module with the module cache key `[specifier, attributes]`.
    // In this example, we just use the specifier as the key.
    const specifier = request.specifier;

    let requestedModule = moduleMap.get(specifier);
    if (requestedModule === undefined) {
      requestedModule = 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 });
      moduleMap.set(specifier, linkedModule);
      // Resolve the dependencies of the new module as well.
      resolveAndLinkDependencies(requestedModule);
    }

    return requestedModule;
  });

  module.linkRequests(requestedModules);
}

resolveAndLinkDependencies(rootModule);
rootModule.instantiate();

// Step 3
//
// Evaluate the Module. The evaluate() method returns a promise which will
// resolve after the module has finished evaluating.

// Prints 42.
await rootModule.evaluate();
    • 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 with throw undefined;.

      Corresponds to the [[EvaluationError]] field of Cyclic Module Record s in the ECMAScript specification.

    • identifier: string

      The identifier of the current module, as set in the constructor.

    • 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, but module.evaluate() has not yet been called.
      • 'evaluating': The module is being evaluated through a module.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 not undefined.

    • options?: ModuleEvaluateOptions
      ): 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.

      @returns

      Fulfills with undefined upon success.

  • class Script

    Instances of the vm.Script class contain precompiled scripts that can be executed in specific contexts.

    • cachedData?: NonSharedBuffer
    • cachedDataRejected?: boolean

      When cachedData is supplied to create the vm.Script, this value will be set to either true or false depending on acceptance of the data by V8. Otherwise the value is undefined.

    • sourceMapURL: undefined | 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
    • createCachedData(): NonSharedBuffer;

      Creates a code cache that can be used with the Script constructor's cachedData option. Returns a Buffer. 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 new Script instances multiple times.

      Functions in the Script source can be marked as lazily compiled and they are not compiled at construction of the Script. 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 the Script 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()`.
    • contextifiedObject: Context,
      options?: RunningScriptOptions
      ): any;

      Runs the compiled code contained by the vm.Script object within the given contextifiedObject 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 or breakOnSigint options will result in new event loops and corresponding threads being started, which have a non-zero performance overhead.

      @param contextifiedObject

      A contextified object as returned by the vm.createContext() method.

      @returns

      the result of the very last statement executed in the script.

    • contextObject?: number | Context,
      options?: RunningScriptInNewContextOptions
      ): any;

      This method is a shortcut to script.runInContext(vm.createContext(options), options). It does several things at once:

      1. Creates a new context.
      2. If contextObject is an object, contextifies it with the new context. If contextObject is undefined, creates a new object and contextifies it. If contextObject is vm.constants.DONT_CONTEXTIFY, don't contextify anything.
      3. 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.
      4. 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 contextObject

      Either vm.constants.DONT_CONTEXTIFY or an object that will be contextified. If undefined, an empty contextified object will be created for backwards compatibility.

      @returns

      the result of the very last statement executed in the script.

    • options?: RunningScriptOptions
      ): any;

      Runs the compiled code contained by the vm.Script within the context of the current global object. Running code does not have access to local scope, but does have access to the current global 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
      @returns

      the 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.

    • 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 with throw undefined;.

      Corresponds to the [[EvaluationError]] field of Cyclic Module Record s in the ECMAScript specification.

    • identifier: string

      The identifier of the current module, as set in the constructor.

    • readonly moduleRequests: readonly ModuleRequest[]

      The requested import dependencies of this module. The returned array is frozen to disallow any changes to it.

      For example, given a source text:

      import foo from 'foo';
import fooAlias from 'foo';
import bar from './bar.js';
import withAttrs from '../with-attrs.ts' with { arbitraryAttr: 'attr-val' };
import source Module from 'wasm-mod.wasm';

      The value of the sourceTextModule.moduleRequests will be:

      [
  {
    specifier: 'foo',
    attributes: {},
    phase: 'evaluation',
  },
  {
    specifier: 'foo',
    attributes: {},
    phase: 'evaluation',
  },
  {
    specifier: './bar.js',
    attributes: {},
    phase: 'evaluation',
  },
  {
    specifier: '../with-attrs.ts',
    attributes: { arbitraryAttr: 'attr-val' },
    phase: 'evaluation',
  },
  {
    specifier: 'wasm-mod.wasm',
    attributes: {},
    phase: 'source',
  },
];
    • 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, but module.evaluate() has not yet been called.
      • 'evaluating': The module is being evaluated through a module.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 not undefined.

    • options?: ModuleEvaluateOptions
      ): 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.

      @returns

      Fulfills with undefined upon success.

    • hasAsyncGraph(): boolean;

      Iterates over the dependency graph and returns true if any module in its dependencies or this module itself contains top-level await expressions, otherwise returns false.

      The search may be slow if the graph is big enough.

      This requires the module to be instantiated first. If the module is not instantiated yet, an error will be thrown.

    • hasTopLevelAwait(): boolean;

      Returns whether the module itself contains any top-level await expressions.

      This corresponds to the field [[HasTLA]] in Cyclic Module Record in the ECMAScript specification.

    • instantiate(): void;

      Instantiate the module with the linked requested modules.

      This resolves the imported bindings of the module, including re-exported binding names. When there are any bindings that cannot be resolved, an error would be thrown synchronously.

      If the requested modules include cyclic dependencies, the sourceTextModule.linkRequests(modules) method must be called on all modules in the cycle before calling this method.

    • modules: readonly Module[]
      ): void;

      Link module dependencies. This method must be called before evaluation, and can only be called once per module.

      The order of the module instances in the modules array should correspond to the order of sourceTextModule.moduleRequests being resolved. If two module requests have the same specifier and import attributes, they must be resolved with the same module instance or an ERR_MODULE_LINK_MISMATCH would be thrown. For example, when linking requests for this module:

      import foo from 'foo';
import source Foo from 'foo';

      The modules array must contain two references to the same instance, because the two module requests are identical but in two phases.

      If the module has no dependencies, the modules array can be empty.

      Users can use sourceTextModule.moduleRequests to implement the host-defined HostLoadImportedModule abstract operation in the ECMAScript specification, and using sourceTextModule.linkRequests() to invoke specification defined FinishLoadingImportedModule, on the module with all dependencies in a batch.

      It's up to the creator of the SourceTextModule to determine if the resolution of the dependencies is synchronous or asynchronous.

      After each module in the modules array is linked, call sourceTextModule.instantiate().

      @param modules

      Array of vm.Module objects that this module depends on. The order of the modules in the array is the order of sourceTextModule.moduleRequests.

  • 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...
    • 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 with throw undefined;.

      Corresponds to the [[EvaluationError]] field of Cyclic Module Record s in the ECMAScript specification.

    • identifier: string

      The identifier of the current module, as set in the constructor.

    • 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, but module.evaluate() has not yet been called.
      • 'evaluating': The module is being evaluated through a module.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 not undefined.

    • options?: ModuleEvaluateOptions
      ): 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.

      @returns

      Fulfills with undefined upon success.

    • name: string,
      value: any
      ): void;

      This method sets the module export binding slots with the given value.

      import vm from 'node:vm';

const m = new vm.SyntheticModule(['x'], () => {
  m.setExport('x', 1);
});

await m.evaluate();

assert.strictEqual(m.namespace.x, 1);
      @param name

      Name of the export to set.

      @param value

      The value to set the export to.

  • function compileFunction(
    code: string,
    params?: readonly string[],
    options?: CompileFunctionOptions
    ): Function & Pick<Script, 'cachedData' | 'cachedDataProduced' | 'cachedDataRejected'>;

    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 code

    The body of the function to compile.

    @param params

    An array of strings containing all parameters for the function.

  • function createContext(
    contextObject?: number | Context,
    options?: CreateContextOptions

    If the given contextObject is an object, the vm.createContext() method will prepare that object and return a reference to it so that it can be used in calls to runInContext or script.runInContext(). Inside such scripts, the global object will be wrapped by the contextObject, 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 as undefined), 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 the contextObject argument. See the documentation of vm.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 and origin of the context are made visible through the Inspector API.

    @param contextObject

    Either vm.constants.DONT_CONTEXTIFY or an object that will be contextified. If undefined, an empty contextified object will be created for backwards compatibility.

    @returns

    contextified object.

  • function isContext(
    sandbox: Context
    ): boolean;

    Returns true if the given object object has been contextified using createContext, or if it's the global object of a context created using vm.constants.DONT_CONTEXTIFY.

  • function measureMemory(
    options?: MeasureMemoryOptions
    ): Promise<MemoryMeasurement>;

    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 that vm.measureMemory() measure the memory reachable by each V8 specific contexts in the current instance of the V8 engine, while the result of v8.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);
  });
  • function runInContext(
    code: string,
    contextifiedObject: Context,
    options?: string | RunningCodeOptions
    ): any;

    The vm.runInContext() method compiles code, runs it within the context of the contextifiedObject, then returns the result. Running code does not have access to the local scope. The contextifiedObject object must have been previously contextified 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 code

    The JavaScript code to compile and run.

    @param contextifiedObject

    The contextified object that will be used as the global when the code is compiled and run.

    @returns

    the result of the very last statement executed in the script.

  • function runInNewContext(
    code: string,
    contextObject?: number | Context,
    options?: string | RunningCodeInNewContextOptions
    ): any;

    This method is a shortcut to (new vm.Script(code, options)).runInContext(vm.createContext(options), options). If options is a string, then it specifies the filename.

    It does several things at once:

    1. Creates a new context.
    2. If contextObject is an object, contextifies it with the new context. If contextObject is undefined, creates a new object and contextifies it. If contextObject is vm.constants.DONT_CONTEXTIFY, don't contextify anything.
    3. Compiles the code as avm.Script
    4. Runs the compield code within the created context. The code does not have access to the scope in which this method is called.
    5. 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 code

    The JavaScript code to compile and run.

    @param contextObject

    Either vm.constants.DONT_CONTEXTIFY or an object that will be contextified. If undefined, an empty contextified object will be created for backwards compatibility.

    @returns

    the result of the very last statement executed in the script.

  • code: string,
    options?: string | RunningCodeOptions
    ): any;

    vm.runInThisContext() compiles code, runs it within the context of the current global and returns the result. Running code does not have access to local scope, but does have access to the current global object.

    If options is a string, then it specifies the filename.

    The following example illustrates using both vm.runInThisContext() and the JavaScript eval() 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 value localVar is changed. In this way vm.runInThisContext() is much like an indirect eval() 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 import node:http on its own, or have a reference to the node: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 code

    The JavaScript code to compile and run.

    @returns

    the 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.

    • filename?: string

      Specifies the filename used 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?: ArrayBufferView<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

    • filename?: string

      Specifies the filename used in stack traces produced by this script.

    • importModuleDynamically?: number | DynamicModuleLoader<Function & Pick<Script, 'cachedData' | 'cachedDataProduced' | 'cachedDataRejected'>>

      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 dynamic import() in compilation APIs.

    • lineOffset?: number

      Specifies the line number offset that is displayed in stack traces produced by this script.

    • parsingContext?: Context

      The sandbox/context in which the said function should be compiled in.

  • interface Context

  • interface CreateContextOptions

    • codeGeneration?: { strings: boolean; wasm: boolean }
    • importModuleDynamically?: number | DynamicModuleLoader<Context>

      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 dynamic import() in compilation APIs.

    • microtaskMode?: 'afterEvaluate'

      If set to afterEvaluate, microtasks will be run immediately after the script has run.

    • name?: string

      Human-readable name of the newly created context.

    • 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 the url.origin property of a URL object. Most notably, this string should omit the trailing slash, as that denotes a path.

  • interface MeasureMemoryOptions

  • interface MemoryMeasurement

    • total: { jsMemoryEstimate: number; jsMemoryRange: [number, number] }

  • interface ModuleEvaluateOptions

    • breakOnSigint?: boolean

      If true, the execution will be terminated when SIGINT (Ctrl+C) is received. Existing handlers for the event that have been attached via process.on('SIGINT') will be disabled during script execution, but will continue to work after that. If execution is terminated, an Error will be thrown.

    • 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 ModuleRequest

    A ModuleRequest represents the request to import a module with given import attributes and phase.

    • attributes: ImportAttributes

      The "with" value passed to the WithClause in a ImportDeclaration, or an empty object if no value was provided.

    • phase: ImportPhase

      The phase of the requested module ("source" or "evaluation").

    • specifier: string

      The specifier of the requested module.

  • interface RunningCodeInNewContextOptions

    • breakOnSigint?: boolean

      If true, the execution will be terminated when SIGINT (Ctrl+C) is received. Existing handlers for the event that have been attached via process.on('SIGINT') will be disabled during script execution, but will continue to work after that. If execution is terminated, an Error will be thrown.

    • cachedData?: ArrayBufferView<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.

    • contextCodeGeneration?: { strings: boolean; wasm: boolean }
    • contextName?: string

      Human-readable name of the newly created context.

    • 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 a URL object. Most notably, this string should omit the trailing slash, as that denotes a path.

    • displayErrors?: boolean

      When true, if an Error occurs while compiling the code, the line of code causing the error is attached to the stack trace.

    • filename?: string

      Specifies the filename used in stack traces produced by this script.

    • importModuleDynamically?: number | DynamicModuleLoader<Script>

      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 dynamic import() in compilation APIs.

    • 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 when SIGINT (Ctrl+C) is received. Existing handlers for the event that have been attached via process.on('SIGINT') will be disabled during script execution, but will continue to work after that. If execution is terminated, an Error will be thrown.

    • cachedData?: ArrayBufferView<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.

    • displayErrors?: boolean

      When true, if an Error occurs while compiling the code, the line of code causing the error is attached to the stack trace.

    • filename?: string

      Specifies the filename used in stack traces produced by this script.

    • importModuleDynamically?: number | DynamicModuleLoader<Script>

      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 dynamic import() in compilation APIs.

    • 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 when SIGINT (Ctrl+C) is received. Existing handlers for the event that have been attached via process.on('SIGINT') will be disabled during script execution, but will continue to work after that. If execution is terminated, an Error will be thrown.

    • columnOffset?: number

      Specifies the column number offset that is displayed in stack traces produced by this script.

    • contextCodeGeneration?: { strings: boolean; wasm: boolean }
    • contextName?: string

      Human-readable name of the newly created context.

    • 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 a URL object. Most notably, this string should omit the trailing slash, as that denotes a path.

    • displayErrors?: boolean

      When true, if an Error occurs while compiling the code, the line of code causing the error is attached to the stack trace.

    • filename?: string

      Specifies the filename used in stack traces produced by this script.

    • 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 when SIGINT (Ctrl+C) is received. Existing handlers for the event that have been attached via process.on('SIGINT') will be disabled during script execution, but will continue to work after that. If execution is terminated, an Error 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 an Error occurs while compiling the code, the line of code causing the error is attached to the stack trace.

    • filename?: string

      Specifies the filename used in stack traces produced by this script.

    • 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?: ArrayBufferView<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.

    • filename?: string

      Specifies the filename used in stack traces produced by this script.

    • importModuleDynamically?: number | DynamicModuleLoader<Script>

      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 dynamic import() in compilation APIs.

    • lineOffset?: number

      Specifies the line number offset that is displayed in stack traces produced by this script.

  • interface SourceTextModuleOptions

  • interface SyntheticModuleOptions

    • context?: Context

      The contextified object as returned by the vm.createContext() method, to compile and evaluate this module in.

    • identifier?: string

      String used in stack traces.

  • type DynamicModuleLoader<T> = (specifier: string, referrer: T, importAttributes: ImportAttributes, phase: ImportPhase) => Module | Promise<Module>
  • type MeasureMemoryMode = 'summary' | 'detailed'
  • type ModuleLinker = (specifier: string, referencingModule: Module, extra: { attributes: ImportAttributes }) => Module | Promise<Module>
  • type ModuleStatus = 'unlinked' | 'linking' | 'linked' | 'evaluating' | 'evaluated' | 'errored'