VM (executing JavaScript)

Added in: v0.10.0

源代码: lib/vm.js

The node:vm module enables compiling and running code within V8 Virtual Machine contexts.

JavaScript code can be compiled and run immediately or compiled, saved, and run later.

A common use case is to run the code in a different V8 Context. This means invoked code has a different global object than the invoking code.

One can provide the context by contextifying an object. The invoked code treats any property in the context like a global variable. Any changes to global variables caused by the invoked code are reflected in the context object.

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C vm.Script

Added in: v0.3.1

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

M new vm.Script(code[, options])

• code string The JavaScript code to compile.
• options Object | string
  • filename string Specifies the filename used in stack traces produced by this script. Default: 'evalmachine.<anonymous>'.
  • lineOffset number Specifies the line number offset that is displayed in stack traces produced by this script. Default: 0.
  • columnOffset number Specifies the first-line column number offset that is displayed in stack traces produced by this script. Default: 0.
  • cachedData Buffer | TypedArray | DataView Provides an optional Buffer or TypedArray, or DataView with V8's code cache data for the supplied source. When supplied, the cachedDataRejected value will be set to either true or false depending on acceptance of the data by V8.
  • produceCachedData boolean When true and no cachedData is present, V8 will attempt to produce code cache data for code. Upon success, a Buffer with V8's code cache data will be produced and stored in the cachedData property of the returned vm.Script instance. The cachedDataProduced value will be set to either true or false depending on whether code cache data is produced successfully. This option is deprecated in favor of script.createCachedData(). Default: false.
  • importModuleDynamically Function Called during evaluation of this module when import() is called. If this option is not specified, calls to import() will reject with ERR_VM_DYNAMIC_IMPORT_CALLBACK_MISSING. This option is part of the experimental modules API. We do not recommend using it in a production environment.
    • specifier string specifier passed to import()
    • script vm.Script
    • importAssertions Object The "assert" value passed to the optionsExpression optional parameter, or an empty object if no value was provided.
    • Returns: Module Namespace Object | vm.Module Returning a vm.Module is recommended in order to take advantage of error tracking, and to avoid issues with namespaces that contain then function exports.

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

Creating a new vm.Script object compiles code but does not run it. The compiled vm.Script can be run later multiple times. The code is not bound to any global object; rather, it is bound before each run, just for that run.

M script.cachedDataRejected

Added in: v5.7.0

• boolean | undefined

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.

M script.createCachedData()

Added in: v10.6.0

• Returns: Buffer

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.

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M script.runInContext(contextifiedObject[, options])

• contextifiedObject Object A contextified object as returned by the vm.createContext() method.
• options Object
  • 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. Default: true.
  • timeout integer 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.
  • breakOnSigint boolean If true, receiving SIGINT (Ctrl+C) will terminate execution and throw an Error. Existing handlers for the event that have been attached via process.on('SIGINT') are disabled during script execution, but continue to work after that. Default: false.
• Returns: any the result of the very last statement executed in the script.

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.

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Using the timeout or breakOnSigint options will result in new event loops and corresponding threads being started, which have a non-zero performance overhead.

M script.runInNewContext([contextObject[, options]])

• contextObject Object An object that will be contextified. If undefined, a new object will be created.
• options Object
  • 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. Default: true.
  • timeout integer 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.
  • breakOnSigint boolean If true, receiving SIGINT (Ctrl+C) will terminate execution and throw an Error. Existing handlers for the event that have been attached via process.on('SIGINT') are disabled during script execution, but continue to work after that. Default: false.
  • contextName string Human-readable name of the newly created context. Default: 'VM Context i', where i is an ascending numerical index of the 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. Default: ''.
  • contextCodeGeneration Object
    • strings boolean If set to false any calls to eval or function constructors (Function, GeneratorFunction, etc) will throw an EvalError. Default: true.
    • wasm boolean If set to false any attempt to compile a WebAssembly module will throw a WebAssembly.CompileError. Default: true.
  • microtaskMode string If set to afterEvaluate, microtasks (tasks scheduled through Promises and async functions) will be run immediately after the script has run. They are included in the timeout and breakOnSigint scopes in that case.
• Returns: any the result of the very last statement executed in the script.

First contextifies the given contextObject, runs the compiled code contained by the vm.Script object within the created context, and returns the result. Running code does not have access to local scope.

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.

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M script.runInThisContext([options])

• options Object
  • 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. Default: true.
  • timeout integer 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.
  • breakOnSigint boolean If true, receiving SIGINT (Ctrl+C) will terminate execution and throw an Error. Existing handlers for the event that have been attached via process.on('SIGINT') are disabled during script execution, but continue to work after that. Default: false.
• Returns: any the result of the very last statement executed in the script.

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:

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M script.sourceMapURL

Added in: v19.1.0

• string | undefined

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.

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C vm.Module

Added in: v13.0.0, v12.16.0

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. Operations on vm.Module objects are intrinsically asynchronous, in contrast with the synchronous nature of vm.Script objects. The use of 'async' functions can help with manipulating vm.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.

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M module.dependencySpecifiers

• 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 Records in the ECMAScript specification.

M module.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 Records in the ECMAScript specification.

M module.evaluate([options])

• options Object
  • timeout integer Specifies the number of milliseconds to evaluate before terminating execution. If execution is interrupted, an Error will be thrown. This value must be a strictly positive integer.
  • breakOnSigint boolean If true, receiving SIGINT (Ctrl+C) will terminate execution and throw an Error. Existing handlers for the event that have been attached via process.on('SIGINT') are disabled during script execution, but continue to work after that. Default: false.
• Returns: Promise Fulfills with undefined upon success.

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 Records in the ECMAScript specification.

M module.identifier

• string

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

M module.link(linker)

• linker Function

  • specifier string The specifier of the requested module:

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  • referencingModule vm.Module The Module object link() is called on.

  • extra Object

    • assert Object The data from the assertion:

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      Per ECMA-262, hosts are expected to ignore assertions that they do not support, as opposed to, for example, triggering an error if an unsupported assertion is present.

  • Returns: vm.Module | Promise

• Returns: Promise

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 a Promise that eventually resolves to a Module object. The returned Module 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's status is 'unlinked', this method will be recursively called on the returned Module with the same provided linker function.

link() returns a Promise that will either get resolved when all linking instances resolve to a valid Module, or rejected if the linker function either throws an exception or returns an invalid Module.

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 Records in the ECMAScript specification.

M module.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.

M module.status

• string

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.

C vm.SourceTextModule

Added in: v9.6.0

This feature is only available with the --experimental-vm-modules command flag enabled.

• Extends: vm.Module

The vm.SourceTextModule class provides the Source Text Module Record as defined in the ECMAScript specification.

M new vm.SourceTextModule(code[, options])

• code string JavaScript Module code to parse
• options
  • identifier string String used in stack traces. Default: 'vm:module(i)' where i is a context-specific ascending index.
  • cachedData Buffer | TypedArray | DataView Provides an optional Buffer or TypedArray, or DataView with V8's code cache data for the supplied source. The code must be the same as the module from which this cachedData was created.
  • context Object The contextified object as returned by the vm.createContext() method, to compile and evaluate this Module in.
  • lineOffset integer Specifies the line number offset that is displayed in stack traces produced by this Module. Default: 0.
  • columnOffset integer Specifies the first-line column number offset that is displayed in stack traces produced by this Module. Default: 0.
  • initializeImportMeta Function Called during evaluation of this Module to initialize the import.meta.
    • meta import.meta
    • module vm.SourceTextModule
  • importModuleDynamically Function Called during evaluation of this module when import() is called. If this option is not specified, calls to import() will reject with ERR_VM_DYNAMIC_IMPORT_CALLBACK_MISSING.
    • specifier string specifier passed to import()
    • module vm.Module
    • importAssertions Object The "assert" value passed to the optionsExpression optional parameter, or an empty object if no value was provided.
    • Returns: Module Namespace Object | vm.Module Returning a vm.Module is recommended in order to take advantage of error tracking, and to avoid issues with namespaces that contain then function exports.

Creates a new SourceTextModule instance.

Properties assigned to the import.meta object that are objects may allow the module to access information outside the specified context. Use vm.runInContext() to create objects in a specific context.

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M sourceTextModule.createCachedData()

Added in: v13.7.0, v12.17.0

• Returns: Buffer

Creates a code cache that can be used with the SourceTextModule constructor's cachedData option. Returns a Buffer. This method may be called any number of times before the module has been evaluated.

The code cache of the SourceTextModule 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 SourceTextModule instances multiple times.

Functions in the SourceTextModule source can be marked as lazily compiled and they are not compiled at construction of the SourceTextModule. 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 SourceTextModule that it can use to speed up future compilations.

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C vm.SyntheticModule

Added in: v13.0.0, v12.16.0

This feature is only available with the --experimental-vm-modules command flag enabled.

• Extends: vm.Module

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.

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M new vm.SyntheticModule(exportNames, evaluateCallback[, options])

Added in: v13.0.0, v12.16.0

• exportNames string[] Array of names that will be exported from the module.
• evaluateCallback Function Called when the module is evaluated.
• options
  • identifier string String used in stack traces. Default: 'vm:module(i)' where i is a context-specific ascending index.
  • context Object The contextified object as returned by the vm.createContext() method, to compile and evaluate this Module in.

Creates a new SyntheticModule instance.

Objects assigned to the exports of this instance may allow importers of the module to access information outside the specified context. Use vm.runInContext() to create objects in a specific context.

M syntheticModule.setExport(name, value)

Added in: v13.0.0, v12.16.0

• name string Name of the export to set.
• value any The value to set the export to.

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.

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M vm.compileFunction(code[, params[, options]])

• code string The body of the function to compile.
• params string[] An array of strings containing all parameters for the function.
• options Object
  • filename string Specifies the filename used in stack traces produced by this script. Default: ''.
  • lineOffset number Specifies the line number offset that is displayed in stack traces produced by this script. Default: 0.
  • columnOffset number Specifies the first-line column number offset that is displayed in stack traces produced by this script. Default: 0.
  • cachedData Buffer | TypedArray | DataView Provides an optional Buffer or TypedArray, or DataView with V8's code cache data for the supplied source.
  • produceCachedData boolean Specifies whether to produce new cache data. Default: false.
  • parsingContext Object The contextified object in which the said function should be compiled in.
  • contextExtensions Object[] An array containing a collection of context extensions (objects wrapping the current scope) to be applied while compiling. Default: [].
  • importModuleDynamically Function Called during evaluation of this module when import() is called. If this option is not specified, calls to import() will reject with ERR_VM_DYNAMIC_IMPORT_CALLBACK_MISSING. This option is part of the experimental modules API, and should not be considered stable.
    • specifier string specifier passed to import()
    • function Function
    • importAssertions Object The "assert" value passed to the optionsExpression optional parameter, or an empty object if no value was provided.
    • Returns: Module Namespace Object | vm.Module Returning a vm.Module is recommended in order to take advantage of error tracking, and to avoid issues with namespaces that contain then function exports.
• Returns: Function

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.

M vm.createContext([contextObject[, options]])

• contextObject Object
• options Object
  • name string Human-readable name of the newly created context. Default: 'VM Context i', where i is an ascending numerical index of the created context.
  • origin 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. Default: ''.
  • codeGeneration Object
    • strings boolean If set to false any calls to eval or function constructors (Function, GeneratorFunction, etc) will throw an EvalError. Default: true.
    • wasm boolean If set to false any attempt to compile a WebAssembly module will throw a WebAssembly.CompileError. Default: true.
  • microtaskMode string If set to afterEvaluate, microtasks (tasks scheduled through Promises and async functions) will be run immediately after a script has run through script.runInContext(). They are included in the timeout and breakOnSigint scopes in that case.
• Returns: Object contextified object.

If given a contextObject, the vm.createContext() method will prepare that object so that it can be used in calls to vm.runInContext() or script.runInContext(). Inside such scripts, the contextObject will be the global object, 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.

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If contextObject is omitted (or passed explicitly as undefined), a new, empty contextified object will be returned.

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.

M vm.isContext(object)

Added in: v0.11.7

• object Object
• Returns: boolean

Returns true if the given object object has been contextified using vm.createContext().

M vm.measureMemory([options])

Added in: v13.10.0

Measure the memory known to V8 and used by all contexts known to the current V8 isolate, or the main context.

• options Object Optional.
  • mode string Either 'summary' or 'detailed'. In summary mode, only the memory measured for the main context will be returned. In detailed mode, the memory measured for all contexts known to the current V8 isolate will be returned. Default: 'summary'
  • execution string Either 'default' or 'eager'. With default execution, the promise will not resolve until after the next scheduled garbage collection starts, which may take a while (or never if the program exits before the next GC). With eager execution, the GC will be started right away to measure the memory. Default: 'default'
• Returns: Promise If the memory is successfully measured the promise will resolve with an object containing information about the memory usage.

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.

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M vm.runInContext(code, contextifiedObject[, options])

• code string The JavaScript code to compile and run.
• contextifiedObject Object The contextified object that will be used as the global when the code is compiled and run.
• options Object | string
  • filename string Specifies the filename used in stack traces produced by this script. Default: 'evalmachine.<anonymous>'.
  • lineOffset number Specifies the line number offset that is displayed in stack traces produced by this script. Default: 0.
  • columnOffset number Specifies the first-line column number offset that is displayed in stack traces produced by this script. Default: 0.
  • 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. Default: true.
  • timeout integer 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.
  • breakOnSigint boolean If true, receiving SIGINT (Ctrl+C) will terminate execution and throw an Error. Existing handlers for the event that have been attached via process.on('SIGINT') are disabled during script execution, but continue to work after that. Default: false.
  • cachedData Buffer | TypedArray | DataView Provides an optional Buffer or TypedArray, or DataView with V8's code cache data for the supplied source.
  • importModuleDynamically Function Called during evaluation of this module when import() is called. If this option is not specified, calls to import() will reject with ERR_VM_DYNAMIC_IMPORT_CALLBACK_MISSING. This option is part of the experimental modules API. We do not recommend using it in a production environment.
    • specifier string specifier passed to import()
    • script vm.Script
    • importAssertions Object The "assert" value passed to the optionsExpression optional parameter, or an empty object if no value was provided.
    • Returns: Module Namespace Object | vm.Module Returning a vm.Module is recommended in order to take advantage of error tracking, and to avoid issues with namespaces that contain then function exports.
• Returns: any the result of the very last statement executed in the script.

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 vm.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:

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M vm.runInNewContext(code[, contextObject[, options]])

• code string The JavaScript code to compile and run.
• contextObject Object An object that will be contextified. If undefined, a new object will be created.
• options Object | string
  • filename string Specifies the filename used in stack traces produced by this script. Default: 'evalmachine.<anonymous>'.
  • lineOffset number Specifies the line number offset that is displayed in stack traces produced by this script. Default: 0.
  • columnOffset number Specifies the first-line column number offset that is displayed in stack traces produced by this script. Default: 0.
  • 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. Default: true.
  • timeout integer 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.
  • breakOnSigint boolean If true, receiving SIGINT (Ctrl+C) will terminate execution and throw an Error. Existing handlers for the event that have been attached via process.on('SIGINT') are disabled during script execution, but continue to work after that. Default: false.
  • contextName string Human-readable name of the newly created context. Default: 'VM Context i', where i is an ascending numerical index of the 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. Default: ''.
  • contextCodeGeneration Object
    • strings boolean If set to false any calls to eval or function constructors (Function, GeneratorFunction, etc) will throw an EvalError. Default: true.
    • wasm boolean If set to false any attempt to compile a WebAssembly module will throw a WebAssembly.CompileError. Default: true.
  • cachedData Buffer | TypedArray | DataView Provides an optional Buffer or TypedArray, or DataView with V8's code cache data for the supplied source.
  • importModuleDynamically Function Called during evaluation of this module when import() is called. If this option is not specified, calls to import() will reject with ERR_VM_DYNAMIC_IMPORT_CALLBACK_MISSING. This option is part of the experimental modules API. We do not recommend using it in a production environment.
    • specifier string specifier passed to import()
    • script vm.Script
    • importAssertions Object The "assert" value passed to the optionsExpression optional parameter, or an empty object if no value was provided.
    • Returns: Module Namespace Object | vm.Module Returning a vm.Module is recommended in order to take advantage of error tracking, and to avoid issues with namespaces that contain then function exports.
  • microtaskMode string If set to afterEvaluate, microtasks (tasks scheduled through Promises and async functions) will be run immediately after the script has run. They are included in the timeout and breakOnSigint scopes in that case.
• Returns: any the result of the very last statement executed in the script.

The vm.runInNewContext() first contextifies the given contextObject (or creates a new contextObject if passed as undefined), compiles the code, runs it within the created context, then returns the result. Running code does not have access to the local scope.

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

The following example compiles and executes code that increments a global variable and sets a new one. These globals are contained in the contextObject.

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M vm.runInThisContext(code[, options])

• code string The JavaScript code to compile and run.
• options Object | string
  • filename string Specifies the filename used in stack traces produced by this script. Default: 'evalmachine.<anonymous>'.
  • lineOffset number Specifies the line number offset that is displayed in stack traces produced by this script. Default: 0.
  • columnOffset number Specifies the first-line column number offset that is displayed in stack traces produced by this script. Default: 0.
  • 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. Default: true.
  • timeout integer 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.
  • breakOnSigint boolean If true, receiving SIGINT (Ctrl+C) will terminate execution and throw an Error. Existing handlers for the event that have been attached via process.on('SIGINT') are disabled during script execution, but continue to work after that. Default: false.
  • cachedData Buffer | TypedArray | DataView Provides an optional Buffer or TypedArray, or DataView with V8's code cache data for the supplied source.
  • importModuleDynamically Function Called during evaluation of this module when import() is called. If this option is not specified, calls to import() will reject with ERR_VM_DYNAMIC_IMPORT_CALLBACK_MISSING. This option is part of the experimental modules API. We do not recommend using it in a production environment.
    • specifier string specifier passed to import()
    • script vm.Script
    • importAssertions Object The "assert" value passed to the optionsExpression optional parameter, or an empty object if no value was provided.
    • Returns: Module Namespace Object | vm.Module Returning a vm.Module is recommended in order to take advantage of error tracking, and to avoid issues with namespaces that contain then function exports.
• Returns: any the result of the very last statement executed in the script.

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:

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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 vm.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 call require('node:http') on its own, or have a reference to the node:http module passed to it. For instance:

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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.

What does it mean to "contextify" an object?

All JavaScript executed within Node.js runs within the scope of a "context". According to the V8 Embedder's Guide:

When the method vm.createContext() is called, the contextObject argument (or a newly-created object if contextObject is undefined) is associated internally with a new instance of a V8 Context. This V8 Context provides the code run using the node:vm module's methods with an isolated global environment within which it can operate. The process of creating the V8 Context and associating it with the contextObject is what this document refers to as "contextifying" the object.

Timeout interactions with asynchronous tasks and Promises

Promises and async functions can schedule tasks run by the JavaScript engine asynchronously. By default, these tasks are run after all JavaScript functions on the current stack are done executing. This allows escaping the functionality of the timeout and breakOnSigint options.

For example, the following code executed by vm.runInNewContext() with a timeout of 5 milliseconds schedules an infinite loop to run after a promise resolves. The scheduled loop is never interrupted by the timeout:

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This can be addressed by passing microtaskMode: 'afterEvaluate' to the code that creates the Context:

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In this case, the microtask scheduled through promise.then() will be run before returning from vm.runInNewContext(), and will be interrupted by the timeout functionality. This applies only to code running in a vm.Context, so e.g. vm.runInThisContext() does not take this option.

Promise callbacks are entered into the microtask queue of the context in which they were created. For example, if () => loop() is replaced with just loop in the above example, then loop will be pushed into the global microtask queue, because it is a function from the outer (main) context, and thus will also be able to escape the timeout.

If asynchronous scheduling functions such as process.nextTick(), queueMicrotask(), setTimeout(), setImmediate(), etc. are made available inside a vm.Context, functions passed to them will be added to global queues, which are shared by all contexts. Therefore, callbacks passed to those functions are not controllable through the timeout either.