nan

What is nan?

The 'nan' package stands for 'Native Abstractions for Node.js'. It is a header file that wraps Node.js and V8 APIs, providing a set of utilities for native module developers to create and maintain native addons across Node.js versions.

What are nan's main functionalities?

Simple Asynchronous Operations

This feature allows developers to perform asynchronous operations in their native addons. The code sample demonstrates how to create an asynchronous worker using 'NanAsyncWorker' and queue it with 'NanAsyncQueueWorker'.

const { NanAsyncWorker, NanAsyncQueueWorker } = require('nan');

class MyWorker extends NanAsyncWorker {
  constructor(callback) {
    super(callback);
  }
  Execute() {
    // perform heavy task
  }
  HandleOKCallback() {
    this->callback().Call(0, nullptr);
  }
}

NanAsyncQueueWorker(new MyWorker(new NanCallback(callback)));

Persistent References

This feature provides a way to create persistent references to V8 objects that won't be garbage collected until explicitly cleared. The code sample shows how to create, reset, check, and clear a persistent reference.

const { NanPersistent } = require('nan');

let persistent = new NanPersistent<v8::Object>();

persistent.Reset(obj); // obj is a V8 object
persistent.IsEmpty(); // checks if the persistent handle is empty
persistent.Clear(); // clears the persistent handle

Callbacks

This feature allows native module developers to store and invoke callbacks. The code sample illustrates how to create a 'NanCallback' from a V8 function and invoke it with no arguments.

const { NanCallback } = require('nan');

let callback = new NanCallback(info[0].As<v8::Function>());
callback.Call(0, nullptr);

Other packages similar to nan

node-addon-api

node-addon-api is an alternative to 'nan' that provides a C++ wrapper classes which simplify the use of the Node.js Addon API. It aims to provide a more stable API across Node.js versions and is recommended by the Node.js team as the primary interface for writing native addons.

ffi-napi

ffi-napi is a Node.js addon for loading and calling dynamic libraries using pure JavaScript. It is similar to 'nan' in that it allows interaction with native code, but it focuses on foreign function interfaces rather than providing abstractions for writing native modules.

ref-napi

ref-napi is a package that provides a way to create, access, and manipulate binary data in Buffer instances in Node.js. It is similar to 'nan' in that it deals with native memory management, but it is more focused on buffer manipulation rather than abstracting Node.js and V8 APIs.

README

Native Abstractions for Node.js

A header file filled with macro and utility goodness for making add-on development for Node.js easier across versions 0.8, 0.10, 0.12, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17 and 18.

Current version: 2.16.0

(See CHANGELOG.md for complete ChangeLog)

Thanks to the crazy changes in V8 (and some in Node core), keeping native addons compiling happily across versions, particularly 0.10 to 0.12 to 4.0, is a minor nightmare. The goal of this project is to store all logic necessary to develop native Node.js addons without having to inspect NODE_MODULE_VERSION and get yourself into a macro-tangle.

This project also contains some helper utilities that make addon development a bit more pleasant.

• News & Updates
• Usage
• Example
• API
• Tests
• Known issues
• Governance & Contributing

News & Updates

Usage

Simply add NAN as a dependency in the package.json of your Node addon:

$ npm install --save nan

Pull in the path to NAN in your binding.gyp so that you can use #include <nan.h> in your .cpp files:

"include_dirs" : [
    "<!(node -e \"require('nan')\")"
]

This works like a -I<path-to-NAN> when compiling your addon.

Example

Just getting started with Nan? Take a look at the Node Add-on Examples.

Refer to a quick-start Nan Boilerplate for a ready-to-go project that utilizes basic Nan functionality.

For a simpler example, see the async pi estimation example in the examples directory for full code and an explanation of what this Monte Carlo Pi estimation example does. Below are just some parts of the full example that illustrate the use of NAN.

Yet another example is nan-example-eol. It shows newline detection implemented as a native addon.

Also take a look at our comprehensive C++ test suite which has a plethora of code snippets for your pasting pleasure.

API

Additional to the NAN documentation below, please consult:

• The V8 Getting Started * Guide
• V8 API Documentation
• Node Add-on Documentation

JavaScript-accessible methods

A template is a blueprint for JavaScript functions and objects in a context. You can use a template to wrap C++ functions and data structures within JavaScript objects so that they can be manipulated from JavaScript. See the V8 Embedders Guide section on Templates for further information.

In order to expose functionality to JavaScript via a template, you must provide it to V8 in a form that it understands. Across the versions of V8 supported by NAN, JavaScript-accessible method signatures vary widely, NAN fully abstracts method declaration and provides you with an interface that is similar to the most recent V8 API but is backward-compatible with older versions that still use the now-deceased v8::Argument type.

• Method argument types

• Nan::FunctionCallbackInfo
• Nan::PropertyCallbackInfo
• Nan::ReturnValue

• Method declarations

• Method declaration
• Getter declaration
• Setter declaration
• Property getter declaration
• Property setter declaration
• Property enumerator declaration
• Property deleter declaration
• Property query declaration
• Index getter declaration
• Index setter declaration
• Index enumerator declaration
• Index deleter declaration
• Index query declaration

• Method and template helpers

• Nan::SetMethod()
• Nan::SetPrototypeMethod()
• Nan::SetAccessor()
• Nan::SetNamedPropertyHandler()
• Nan::SetIndexedPropertyHandler()
• Nan::SetTemplate()
• Nan::SetPrototypeTemplate()
• Nan::SetInstanceTemplate()
• Nan::SetCallHandler()
• Nan::SetCallAsFunctionHandler()

Scopes

A local handle is a pointer to an object. All V8 objects are accessed using handles, they are necessary because of the way the V8 garbage collector works.

A handle scope can be thought of as a container for any number of handles. When you've finished with your handles, instead of deleting each one individually you can simply delete their scope.

The creation of HandleScope objects is different across the supported versions of V8. Therefore, NAN provides its own implementations that can be used safely across these.

• Nan::HandleScope
• Nan::EscapableHandleScope

Also see the V8 Embedders Guide section on Handles and Garbage Collection.

Persistent references

An object reference that is independent of any HandleScope is a persistent reference. Where a Local handle only lives as long as the HandleScope in which it was allocated, a Persistent handle remains valid until it is explicitly disposed.

Due to the evolution of the V8 API, it is necessary for NAN to provide a wrapper implementation of the Persistent classes to supply compatibility across the V8 versions supported.

• Nan::PersistentBase & v8::PersistentBase
• Nan::NonCopyablePersistentTraits & v8::NonCopyablePersistentTraits
• Nan::CopyablePersistentTraits & v8::CopyablePersistentTraits
• Nan::Persistent
• Nan::Global
• Nan::WeakCallbackInfo
• Nan::WeakCallbackType

Also see the V8 Embedders Guide section on Handles and Garbage Collection.

New

NAN provides a Nan::New() helper for the creation of new JavaScript objects in a way that's compatible across the supported versions of V8.

• Nan::New()
• Nan::Undefined()
• Nan::Null()
• Nan::True()
• Nan::False()
• Nan::EmptyString()

Converters

NAN contains functions that convert v8::Values to other v8::Value types and native types. Since type conversion is not guaranteed to succeed, they return Nan::Maybe types. These converters can be used in place of value->ToX() and value->XValue() (where X is one of the types, e.g. Boolean) in a way that provides a consistent interface across V8 versions. Newer versions of V8 use the new v8::Maybe and v8::MaybeLocal types for these conversions, older versions don't have this functionality so it is provided by NAN.

• Nan::To()

Maybe Types

The Nan::MaybeLocal and Nan::Maybe types are monads that encapsulate v8::Local handles that may be empty.

• Maybe Types
  • Nan::MaybeLocal
  • Nan::Maybe
  • Nan::Nothing
  • Nan::Just
• Maybe Helpers
  • Nan::Call()
  • Nan::ToDetailString()
  • Nan::ToArrayIndex()
  • Nan::Equals()
  • Nan::NewInstance()
  • Nan::GetFunction()
  • Nan::Set()
  • Nan::DefineOwnProperty()
  • Nan::ForceSet()
  • Nan::Get()
  • Nan::GetPropertyAttributes()
  • Nan::Has()
  • Nan::Delete()
  • Nan::GetPropertyNames()
  • Nan::GetOwnPropertyNames()
  • Nan::SetPrototype()
  • Nan::ObjectProtoToString()
  • Nan::HasOwnProperty()
  • Nan::HasRealNamedProperty()
  • Nan::HasRealIndexedProperty()
  • Nan::HasRealNamedCallbackProperty()
  • Nan::GetRealNamedPropertyInPrototypeChain()
  • Nan::GetRealNamedProperty()
  • Nan::CallAsFunction()
  • Nan::CallAsConstructor()
  • Nan::GetSourceLine()
  • Nan::GetLineNumber()
  • Nan::GetStartColumn()
  • Nan::GetEndColumn()
  • Nan::CloneElementAt()
  • Nan::HasPrivate()
  • Nan::GetPrivate()
  • Nan::SetPrivate()
  • Nan::DeletePrivate()
  • Nan::MakeMaybe()

Script

NAN provides v8::Script helpers as the API has changed over the supported versions of V8.

• Nan::CompileScript()
• Nan::RunScript()
• Nan::ScriptOrigin

JSON

The JSON object provides the C++ versions of the methods offered by the JSON object in javascript. V8 exposes these methods via the v8::JSON object.

• Nan::JSON.Parse
• Nan::JSON.Stringify

Refer to the V8 JSON object in the V8 documentation for more information about these methods and their arguments.

Errors

NAN includes helpers for creating, throwing and catching Errors as much of this functionality varies across the supported versions of V8 and must be abstracted.

Note that an Error object is simply a specialized form of v8::Value.

Also consult the V8 Embedders Guide section on Exceptions for more information.

• Nan::Error()
• Nan::RangeError()
• Nan::ReferenceError()
• Nan::SyntaxError()
• Nan::TypeError()
• Nan::ThrowError()
• Nan::ThrowRangeError()
• Nan::ThrowReferenceError()
• Nan::ThrowSyntaxError()
• Nan::ThrowTypeError()
• Nan::FatalException()
• Nan::ErrnoException()
• Nan::TryCatch

Buffers

NAN's node::Buffer helpers exist as the API has changed across supported Node versions. Use these methods to ensure compatibility.

• Nan::NewBuffer()
• Nan::CopyBuffer()
• Nan::FreeCallback()

Nan::Callback

Nan::Callback makes it easier to use v8::Function handles as callbacks. A class that wraps a v8::Function handle, protecting it from garbage collection and making it particularly useful for storage and use across asynchronous execution.

• Nan::Callback

Asynchronous work helpers

Nan::AsyncWorker, Nan::AsyncProgressWorker and Nan::AsyncProgressQueueWorker are helper classes that make working with asynchronous code easier.

• Nan::AsyncWorker
• Nan::AsyncProgressWorkerBase & Nan::AsyncProgressWorker
• Nan::AsyncProgressQueueWorker
• Nan::AsyncQueueWorker

Strings & Bytes

Miscellaneous string & byte encoding and decoding functionality provided for compatibility across supported versions of V8 and Node. Implemented by NAN to ensure that all encoding types are supported, even for older versions of Node where they are missing.

• Nan::Encoding
• Nan::Encode()
• Nan::DecodeBytes()
• Nan::DecodeWrite()

Object Wrappers

The ObjectWrap class can be used to make wrapped C++ objects and a factory of wrapped objects.

• Nan::ObjectWrap

V8 internals

The hooks to access V8 internals—including GC and statistics—are different across the supported versions of V8, therefore NAN provides its own hooks that call the appropriate V8 methods.

• NAN_GC_CALLBACK()
• Nan::AddGCEpilogueCallback()
• Nan::RemoveGCEpilogueCallback()
• Nan::AddGCPrologueCallback()
• Nan::RemoveGCPrologueCallback()
• Nan::GetHeapStatistics()
• Nan::SetCounterFunction()
• Nan::SetCreateHistogramFunction()
• Nan::SetAddHistogramSampleFunction()
• Nan::IdleNotification()
• Nan::LowMemoryNotification()
• Nan::ContextDisposedNotification()
• Nan::GetInternalFieldPointer()
• Nan::SetInternalFieldPointer()
• Nan::AdjustExternalMemory()

Miscellaneous V8 Helpers

• Nan::Utf8String
• Nan::GetCurrentContext()
• Nan::SetIsolateData()
• Nan::GetIsolateData()
• Nan::TypedArrayContents

Miscellaneous Node Helpers

• Nan::AsyncResource
• Nan::MakeCallback()
• NAN_MODULE_INIT()
• Nan::Export()

Tests

To run the NAN tests do:

npm install
npm run-script rebuild-tests
npm test

Or just:

npm install
make test

Known issues

Compiling against Node.js 0.12 on OSX

With new enough compilers available on OSX, the versions of V8 headers corresponding to Node.js 0.12 do not compile anymore. The error looks something like:

❯   CXX(target) Release/obj.target/accessors/cpp/accessors.o
In file included from ../cpp/accessors.cpp:9:
In file included from ../../nan.h:51:
In file included from /Users/ofrobots/.node-gyp/0.12.18/include/node/node.h:61:
/Users/ofrobots/.node-gyp/0.12.18/include/node/v8.h:5800:54: error: 'CreateHandle' is a protected member of 'v8::HandleScope'
  return Handle<T>(reinterpret_cast<T*>(HandleScope::CreateHandle(
                                        ~~~~~~~~~~~~~^~~~~~~~~~~~

This can be worked around by patching your local versions of v8.h corresponding to Node 0.12 to make v8::Handle a friend of v8::HandleScope. Since neither Node.js not V8 support this release line anymore this patch cannot be released by either project in an official release.

For this reason, we do not test against Node.js 0.12 on OSX in this project's CI. If you need to support that configuration, you will need to either get an older compiler, or apply a source patch to the version of V8 headers as a workaround.

Governance & Contributing

NAN is governed by the Node.js Addon API Working Group

Addon API Working Group (WG)

The NAN project is jointly governed by a Working Group which is responsible for high-level guidance of the project.

Members of the WG are also known as Collaborators, there is no distinction between the two, unlike other Node.js projects.

The WG has final authority over this project including:

• Technical direction
• Project governance and process (including this policy)
• Contribution policy
• GitHub repository hosting
• Maintaining the list of additional Collaborators

For the current list of WG members, see the project README.md.

Individuals making significant and valuable contributions are made members of the WG and given commit-access to the project. These individuals are identified by the WG and their addition to the WG is discussed via GitHub and requires unanimous consensus amongst those WG members participating in the discussion with a quorum of 50% of WG members required for acceptance of the vote.

Note: If you make a significant contribution and are not considered for commit-access log an issue or contact a WG member directly.

For the current list of WG members / Collaborators, see the project README.md.

Consensus Seeking Process

The WG follows a Consensus Seeking decision making model.

Modifications of the contents of the NAN repository are made on a collaborative basis. Anybody with a GitHub account may propose a modification via pull request and it will be considered by the WG. All pull requests must be reviewed and accepted by a WG member with sufficient expertise who is able to take full responsibility for the change. In the case of pull requests proposed by an existing WG member, an additional WG member is required for sign-off. Consensus should be sought if additional WG members participate and there is disagreement around a particular modification.

If a change proposal cannot reach a consensus, a WG member can call for a vote amongst the members of the WG. Simple majority wins.

Developer's Certificate of Origin 1.1

By making a contribution to this project, I certify that:

• (a) The contribution was created in whole or in part by me and I have the right to submit it under the open source license indicated in the file; or

• (b) The contribution is based upon previous work that, to the best of my knowledge, is covered under an appropriate open source license and I have the right under that license to submit that work with modifications, whether created in whole or in part by me, under the same open source license (unless I am permitted to submit under a different license), as indicated in the file; or

• (c) The contribution was provided directly to me by some other person who certified (a), (b) or (c) and I have not modified it.

• (d) I understand and agree that this project and the contribution are public and that a record of the contribution (including all personal information I submit with it, including my sign-off) is maintained indefinitely and may be redistributed consistent with this project or the open source license(s) involved.

WG Members / Collaborators

Rod Vagg	GitHub/rvagg	Twitter/@rvagg
Benjamin Byholm	GitHub/kkoopa	-
Trevor Norris	GitHub/trevnorris	Twitter/@trevnorris
Nathan Rajlich	GitHub/TooTallNate	Twitter/@TooTallNate
Brett Lawson	GitHub/brett19	Twitter/@brett19x
Ben Noordhuis	GitHub/bnoordhuis	Twitter/@bnoordhuis
David Siegel	GitHub/agnat	Twitter/@agnat
Michael Ira Krufky	GitHub/mkrufky	Twitter/@mkrufky

Licence & copyright

Copyright (c) 2018 NAN WG Members / Collaborators (listed above).

Native Abstractions for Node.js is licensed under an MIT license. All rights not explicitly granted in the MIT license are reserved. See the included LICENSE file for more details.