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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 and 0.11, and eventually 0.12.

Current version: 1.0.0 (See nan.h for complete ChangeLog)

NPM NPM

Thanks to the crazy changes in V8 (and some in Node core), keeping native addons compiling happily across versions, particularly 0.10 to 0.11/0.12, 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

May-2014: Major changes for V8 3.25 / Node 0.11.13

Node 0.11.11 and 0.11.12 were both broken releases for native add-ons, you simply can't properly compile against either of them for different reasons. But we now have a 0.11.13 release that jumps a couple of versions of V8 ahead and includes some more, major (traumatic) API changes.

Because we are now nearing Node 0.12 and estimate that the version of V8 we are using in Node 0.11.13 will be close to the API we get for 0.12, we have taken the opportunity to not only fix NAN for 0.11.13 but make some major changes to improve the NAN API.

We have removed support for Node 0.11 versions prior to 0.11.13. As usual, our tests are run against (and pass) the last 5 versions of Node 0.8 and Node 0.10. We also include Node 0.11.13 obviously.

The major change is something that Benjamin Byholm has put many hours in to. We now have a fantastic new NanNew<T>(args) interface for creating new Locals, this replaces NanNewLocal() and much more. If you look in ./nan.h you'll see a large number of overloaded versions of this method. In general you should be able to NanNew<Type>(arguments) for any type you want to make a Local from. This includes Persistent types, so we now have a Local<T> NanNew(const Persistent<T> arg) to replace NanPersistentToLocal().

We also now have NanUndefined(), NanNull(), NanTrue() and NanFalse(). Mainly because of the new requirement for an Isolate argument for each of the native V8 versions of this.

V8 has now introduced an EscapableHandleScope from which you scope.Escape(Local<T> value) to return a value from a one scope to another. This replaces the standard HandleScope and scope.Close(Local<T> value), although HandleScope still exists for when you don't need to return a handle to the caller. For NAN we are exposing it as NanEscapableScope() and NanEscapeScope(), while NanScope() is still how you create a new scope that doesn't need to return handles. For older versions of Node/V8, it'll still map to the older HandleScope functionality.

NanFromV8String() was deprecated and has now been removed. You should use NanCString() or NanRawString() instead.

Because node::MakeCallback() now takes an Isolate, and because it doesn't exist in older versions of Node, we've introduced NanMakeCallabck(). You should always use this when calling a JavaScript function from C++.

There's lots more, check out the Changelog in nan.h or look through #86 for all the gory details.

Dec-2013: NanCString and NanRawString

Two new functions have been introduced to replace the functionality that's been provided by NanFromV8String until now. NanCString has sensible defaults so it's super easy to fetch a null-terminated c-style string out of a v8::String. NanFromV8String is still around and has defaults that allow you to pass a single handle to fetch a char* while NanRawString requires a little more attention to arguments.

Nov-2013: Node 0.11.9+ breaking V8 change

The version of V8 that's shipping with Node 0.11.9+ has changed the signature for new Locals to: v8::Local<T>::New(isolate, value), i.e. introducing the isolate argument and therefore breaking all new Local declarations for previous versions. NAN 0.6+ now includes a NanNewLocal<T>(value) that can be used in place to work around this incompatibility and maintain compatibility with 0.8->0.11.9+ (minus a few early 0.11 releases).

For example, if you wanted to return a null on a callback you will have to change the argument from v8::Local<v8::Value>::New(v8::Null()) to NanNewLocal<v8::Value>(v8::Null()).

Nov-2013: Change to binding.gyp "include_dirs" for NAN

Inclusion of NAN in a project's binding.gyp is now greatly simplified. You can now just use "<!(node -e \"require('nan')\")" in your "include_dirs", see example below (note Windows needs the quoting around require to be just right: "require('nan')" with appropriate \ escaping).

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

See LevelDOWN for a full example of NAN in use.

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.

Compare to the current 0.10 version of this example, found in the node-addon-examples repository and also a 0.11 version of the same found here.

Note that there is no embedded version sniffing going on here and also the async work is made much simpler, see below for details on the NanAsyncWorker class.

// addon.cc
#include <node.h>
#include <nan.h>
// ...

using v8::FunctionTemplate;
using v8::Handle;
using v8::Object;

void InitAll(Handle<Object> exports) {
  exports->Set(NanSymbol("calculateSync"),
    NanNew<FunctionTemplate>(CalculateSync)->GetFunction());

  exports->Set(NanSymbol("calculateAsync"),
    NanNew<FunctionTemplate>(CalculateAsync)->GetFunction());
}

NODE_MODULE(addon, InitAll)
// sync.h
#include <node.h>
#include <nan.h>

NAN_METHOD(CalculateSync);
// sync.cc
#include <node.h>
#include <nan.h>
#include "./sync.h"
// ...

using v8::Number;

// Simple synchronous access to the `Estimate()` function
NAN_METHOD(CalculateSync) {
  NanScope();

  // expect a number as the first argument
  int points = args[0]->Uint32Value();
  double est = Estimate(points);

  NanReturnValue(NanNew<Number>(est));
}
// async.cc
#include <node.h>
#include <nan.h>
#include "./async.h"

// ...

using v8::Function;
using v8::Local;
using v8::Null;
using v8::Number;
using v8::Value;

class PiWorker : public NanAsyncWorker {
 public:
  PiWorker(NanCallback *callback, int points)
    : NanAsyncWorker(callback), points(points) {}
  ~PiWorker() {}

  // Executed inside the worker-thread.
  // It is not safe to access V8, or V8 data structures
  // here, so everything we need for input and output
  // should go on `this`.
  void Execute () {
    estimate = Estimate(points);
  }

  // Executed when the async work is complete
  // this function will be run inside the main event loop
  // so it is safe to use V8 again
  void HandleOKCallback () {
    NanScope();

    Local<Value> argv[] = {
        NanNull()
      , NanNew<Number>(estimate)
    };

    callback->Call(2, argv);
  };

 private:
  int points;
  double estimate;
};

// Asynchronous access to the `Estimate()` function
NAN_METHOD(CalculateAsync) {
  NanScope();

  int points = args[0]->Uint32Value();
  NanCallback *callback = new NanCallback(args[1].As<Function>());

  NanAsyncQueueWorker(new PiWorker(callback, points));
  NanReturnUndefined();
}

API

NAN_METHOD(methodname)

Use NAN_METHOD to define your V8 accessible methods:

// .h:
class Foo : public node::ObjectWrap {
  ...

  static NAN_METHOD(Bar);
  static NAN_METHOD(Baz);
}


// .cc:
NAN_METHOD(Foo::Bar) {
  ...
}

NAN_METHOD(Foo::Baz) {
  ...
}

The reason for this macro is because of the method signature change in 0.11:

// 0.10 and below:
Handle<Value> name(const Arguments& args)

// 0.11 and above
void name(const FunctionCallbackInfo<Value>& args)

The introduction of FunctionCallbackInfo brings additional complications:

NAN_GETTER(methodname)

Use NAN_GETTER to declare your V8 accessible getters. You get a Local<String> property and an appropriately typed args object that can act like the args argument to a NAN_METHOD call.

You can use NanReturnNull(), NanReturnEmptyString(), NanReturnUndefined() and NanReturnValue() in a NAN_GETTER.

NAN_SETTER(methodname)

Use NAN_SETTER to declare your V8 accessible setters. Same as NAN_GETTER but you also get a Local<Value> value object to work with.

NAN_PROPERTY_GETTER(cbname)

Use NAN_PROPERTY_GETTER to declare your V8 accessible property getters. You get a Local<String> property and an appropriately typed args object that can act similar to the args argument to a NAN_METHOD call.

You can use NanReturnNull(), NanReturnEmptyString(), NanReturnUndefined() and NanReturnValue() in a NAN_PROPERTY_GETTER.

NAN_PROPERTY_SETTER(cbname)

Use NAN_PROPERTY_SETTER to declare your V8 accessible property setters. Same as NAN_PROPERTY_GETTER but you also get a Local<Value> value object to work with.

NAN_PROPERTY_ENUMERATOR(cbname)

Use NAN_PROPERTY_ENUMERATOR to declare your V8 accessible property enumerators. You get an appropriately typed args object like the args argument to a NAN_PROPERTY_GETTER call.

You can use NanReturnNull(), NanReturnEmptyString(), NanReturnUndefined() and NanReturnValue() in a NAN_PROPERTY_ENUMERATOR.

NAN_PROPERTY_DELETER(cbname)

Use NAN_PROPERTY_DELETER to declare your V8 accessible property deleters. Same as NAN_PROPERTY_GETTER.

You can use NanReturnNull(), NanReturnEmptyString(), NanReturnUndefined() and NanReturnValue() in a NAN_PROPERTY_DELETER.

NAN_PROPERTY_QUERY(cbname)

Use NAN_PROPERTY_QUERY to declare your V8 accessible property queries. Same as NAN_PROPERTY_GETTER.

You can use NanReturnNull(), NanReturnEmptyString(), NanReturnUndefined() and NanReturnValue() in a NAN_PROPERTY_QUERY.

NAN_INDEX_GETTER(cbname)

Use NAN_INDEX_GETTER to declare your V8 accessible index getters. You get a uint32_t index and an appropriately typed args object that can act similar to the args argument to a NAN_METHOD call.

You can use NanReturnNull(), NanReturnEmptyString(), NanReturnUndefined() and NanReturnValue() in a NAN_INDEX_GETTER.

NAN_INDEX_SETTER(cbname)

Use NAN_INDEX_SETTER to declare your V8 accessible index setters. Same as NAN_INDEX_GETTER but you also get a Local<Value> value object to work with.

NAN_INDEX_ENUMERATOR(cbname)

Use NAN_INDEX_ENUMERATOR to declare your V8 accessible index enumerators. You get an appropriately typed args object like the args argument to a NAN_INDEX_GETTER call.

You can use NanReturnNull(), NanReturnEmptyString(), NanReturnUndefined() and NanReturnValue() in a NAN_INDEX_ENUMERATOR.

NAN_INDEX_DELETER(cbname)

Use NAN_INDEX_DELETER to declare your V8 accessible index deleters. Same as NAN_INDEX_GETTER.

You can use NanReturnNull(), NanReturnEmptyString(), NanReturnUndefined() and NanReturnValue() in a NAN_INDEX_DELETER.

NAN_INDEX_QUERY(cbname)

Use NAN_INDEX_QUERY to declare your V8 accessible index queries. Same as NAN_INDEX_GETTER.

You can use NanReturnNull(), NanReturnEmptyString(), NanReturnUndefined() and NanReturnValue() in a NAN_INDEX_QUERY.

NAN_WEAK_CALLBACK(cbname)

Use NAN_WEAK_CALLBACK to define your V8 WeakReference callbacks. Do not use for declaration. There is an argument object const _NanWeakCallbackData<T, P> &data allowing access to the weak object and the supplied parameter through its GetValue and GetParameter methods. You can even access the weak callback info object through the GetCallbackInfo()method, but you probably should not. You must either Revive() the weak handle or Dispose() it among with the callback info structure.

NAN_WEAK_CALLBACK(weakCallback) {
  int *parameter = data.GetParameter();
  NanMakeCallback(NanGetCurrentContext()->Global(), data.GetValue(), 0, NULL);
  if ((*parameter)++ == 0) {
    data.Revive();
  } else {
    delete parameter;
    data.Dispose();
  }
}

NAN_DEPRECATED

Declares a function as deprecated.

static NAN_DEPRECATED NAN_METHOD(foo) {
  ...
}

NAN_INLINE

Inlines a function.

NAN_INLINE int foo(int bar) {
  ...
}

Local<T> NanNew<T>( ... )

Use NanNew to construct almost all v8 objects and make new local handles.

Local<String> s = NanNew<String>("value");

...

Persistent<Object> o;

...

Local<Object> lo = NanNew(o);

Local<Primitive> NanUndefined()

Use instead of Undefined()

Local<Primitive> NanNull()

Use instead of Null()

Local<Primitive> NanTrue()

Use instead of True()

Local<Primitive> NanFalse()

Use instead of False()

NanReturnValue(Handle<Value>)

Use NanReturnValue when you want to return a value from your V8 accessible method:

NAN_METHOD(Foo::Bar) {
  ...

  NanReturnValue(NanNew<String>("FooBar!"));
}

No return statement required.

NanReturnUndefined()

Use NanReturnUndefined when you don't want to return anything from your V8 accessible method:

NAN_METHOD(Foo::Baz) {
  ...

  NanReturnUndefined();
}

NanReturnNull()

Use NanReturnNull when you want to return Null from your V8 accessible method:

NAN_METHOD(Foo::Baz) {
  ...

  NanReturnNull();
}

NanReturnEmptyString()

Use NanReturnEmptyString when you want to return an empty String from your V8 accessible method:

NAN_METHOD(Foo::Baz) {
  ...

  NanReturnEmptyString();
}

NanScope()

The introduction of isolate references for many V8 calls in Node 0.11 makes NanScope() necessary, use it in place of HandleScope scope:

NAN_METHOD(Foo::Bar) {
  NanScope();

  NanReturnValue(NanNew<String>("FooBar!"));
}

NanEscapableScope()

The separation of handle scopes into escapable and inescapable scopes makes NanEscapableScope() necessary, use it in place of HandleScope scope when you later wish to Close() the scope:

Handle<String> Foo::Bar() {
  NanEscapableScope();

  return NanEscapeScope(NanNew<String>("FooBar!"));
}

Local<T> NanEscapeScope(Handle<T> value);

Use together with NanEscapableScope to escape the scope. Corresponds to HandleScope::Close or EscapableHandleScope::Escape.

NanLocker()

The introduction of isolate references for many V8 calls in Node 0.11 makes NanLocker() necessary, use it in place of Locker locker:

NAN_METHOD(Foo::Bar) {
  NanLocker();
  ...
  NanUnlocker();
}

NanUnlocker()

The introduction of isolate references for many V8 calls in Node 0.11 makes NanUnlocker() necessary, use it in place of Unlocker unlocker:

NAN_METHOD(Foo::Bar) {
  NanLocker();
  ...
  NanUnlocker();
}

void * NanGetInternalFieldPointer(Handle<Object>, int)

Gets a pointer to the internal field with at index from a V8 Object handle.

Local<Object> obj;
...
NanGetInternalFieldPointer(obj, 0);

void NanSetInternalFieldPointer(Handle<Object>, int, void *)

Sets the value of the internal field at index on a V8 Object handle.

static Persistent<Function> dataWrapperCtor;
...
Local<Object> wrapper = NanNew(dataWrapperCtor)->NewInstance();
NanSetInternalFieldPointer(wrapper, 0, this);

Local<Object> NanObjectWrapHandle(Object)

When you want to fetch the V8 object handle from a native object you've wrapped with Node's ObjectWrap, you should use NanObjectWrapHandle:

NanObjectWrapHandle(iterator)->Get(NanSymbol("end"))

String NanSymbol(char *)

Use to create string symbol objects (i.e. v8::String::NewSymbol(x)), for getting and setting object properties, or names of objects.

bool foo = false;
if (obj->Has(NanSymbol("foo")))
  foo = optionsObj->Get(NanSymbol("foo"))->BooleanValue()

Type NanGetPointerSafe(Type *[, Type])

A helper for getting values from optional pointers. If the pointer is NULL, the function returns the optional default value, which defaults to 0. Otherwise, the function returns the value the pointer points to.

char *plugh(uint32_t *optional) {
  char res[] = "xyzzy";
  uint32_t param = NanGetPointerSafe<uint32_t>(optional, 0x1337);
  switch (param) {
    ...
  }
  NanSetPointerSafe<uint32_t>(optional, 0xDEADBEEF);
}

bool NanSetPointerSafe(Type *, Type)

A helper for setting optional argument pointers. If the pointer is NULL, the function simply returns false. Otherwise, the value is assigned to the variable the pointer points to.

const char *plugh(size_t *outputsize) {
  char res[] = "xyzzy";
  if !(NanSetPointerSafe<size_t>(outputsize, strlen(res) + 1)) {
    ...
  }

  ...
}

void* NanRawString(Handle<Value>, enum Nan::Encoding, size_t *, void *, size_t, int)

When you want to convert a V8 String to a char* buffer, use NanRawString. You have to supply an encoding as well as a pointer to a variable that will be assigned the number of bytes in the returned string. It is also possible to supply a buffer and its length to the function in order not to have a new buffer allocated. The final argument allows setting String::WriteOptions. Just remember that you'll end up with an object that you'll need to delete[] at some point unless you supply your own buffer:

size_t count;
void* decoded = NanRawString(args[1], Nan::BASE64, &count, NULL, 0, String::HINT_MANY_WRITES_EXPECTED);
char param_copy[count];
memcpy(param_copy, decoded, count);
delete[] decoded;

char* NanCString(Handle<Value>, size_t *[, char *, size_t, int])

When you want to convert a V8 String to a null-terminated C char* use NanCString. The resulting char* will be UTF-8-encoded, and you need to supply a pointer to a variable that will be assigned the number of bytes in the returned string. It is also possible to supply a buffer and its length to the function in order not to have a new buffer allocated. The final argument allows optionally setting String::WriteOptions, which default to v8::String::NO_OPTIONS. Just remember that you'll end up with an object that you'll need to delete[] at some point unless you supply your own buffer:

size_t count;
char* name = NanCString(args[0], &count);

bool NanBooleanOptionValue(Handle<Value>, Handle<String>[, bool])

When you have an "options" object that you need to fetch properties from, boolean options can be fetched with this pair. They check first if the object exists (IsEmpty), then if the object has the given property (Has) then they get and convert/coerce the property to a bool.

The optional last parameter is the default value, which is false if left off:

// `foo` is false unless the user supplies a truthy value for it
bool foo = NanBooleanOptionValue(optionsObj, NanSymbol("foo"));
// `bar` is true unless the user supplies a falsy value for it
bool bar = NanBooleanOptionValueDefTrue(optionsObj, NanSymbol("bar"), true);

uint32_t NanUInt32OptionValue(Handle<Value>, Handle<String>, uint32_t)

Similar to NanBooleanOptionValue, use NanUInt32OptionValue to fetch an integer option from your options object. Can be any kind of JavaScript Number and it will be coerced to an unsigned 32-bit integer.

Requires all 3 arguments as a default is not optional:

uint32_t count = NanUInt32OptionValue(optionsObj, NanSymbol("count"), 1024);

NanError(message), NanTypeError(message), NanRangeError(message)

For making Error, TypeError and RangeError objects.

Local<Value> res = NanError("you must supply a callback argument");

NanThrowError(message), NanThrowTypeError(message), NanThrowRangeError(message), NanThrowError(Local<Value>), NanThrowError(Local<Value>, int)

For throwing Error, TypeError and RangeError objects. You should return this call:

return NanThrowError("you must supply a callback argument");

Can also handle any custom object you may want to throw. If used with the error code argument, it will add the supplied error code to the error object as a property called code.

Local<Object> NanNewBufferHandle(char *, uint32_t), Local<Object> NanNewBufferHandle(uint32_t)

The Buffer API has changed a little in Node 0.11, this helper provides consistent access to Buffer creation:

NanNewBufferHandle((char*)value.data(), value.size());

Can also be used to initialize a Buffer with just a size argument.

Can also be supplied with a NanFreeCallback and a hint for the garbage collector.

Local<Object> NanBufferUse(char*, uint32_t)

Buffer::New(char*, uint32_t) prior to 0.11 would make a copy of the data. While it was possible to get around this, it required a shim by passing a callback. So the new API Buffer::Use(char*, uint32_t) was introduced to remove needing to use this shim.

NanBufferUse uses the char* passed as the backing data, and will free the memory automatically when the weak callback is called. Keep this in mind, as careless use can lead to "double free or corruption" and other cryptic failures.

bool NanHasInstance(Persistent<FunctionTemplate>&, Handle<Value>)

Can be used to check the type of an object to determine it is of a particular class you have already defined and have a Persistent<FunctionTemplate> handle for.

### Local<Context> NanNewContextHandle([ExtensionConfiguration*, Handle<ObjectTemplate>, Handle<Value>]) Creates a new `Local` handle. 
Local<FunctionTemplate> ftmpl = NanNew<FunctionTemplate>();
Local<ObjectTemplate> otmpl = ftmpl->InstanceTemplate();
Local<Context> ctx =  NanNewContextHandle(NULL, otmpl);
 ### Local<Context> NanGetCurrentContext()

Gets the current context.

Local<Context> ctx = NanGetCurrentContext();

void NanDisposePersistent(Persistent<T> &)

Use NanDisposePersistent to dispose a Persistent handle.

NanDisposePersistent(persistentHandle);

NanAssignPersistent(handle, object)

Use NanAssignPersistent to assign a non-Persistent handle to a Persistent one. You can no longer just declare a Persistent handle and assign directly to it later, you have to Reset it in Node 0.11, so this makes it easier.

In general it is now better to place anything you want to protect from V8's garbage collector as properties of a generic Object and then assign that to a Persistent. This works in older versions of Node also if you use NanAssignPersistent:

Persistent<Object> persistentHandle;

...

Local<Object> obj = NanNew<Object>();
obj->Set(NanSymbol("key"), keyHandle); // where keyHandle might be a Local<String>
NanAssignPersistent(persistentHandle, obj)

_NanWeakCallbackInfo<T, P>* NanMakeWeakPersistent(Handle<T>, P*, _NanWeakCallbackInfo<T, P>::Callback)

Creates a weak persistent handle with the supplied parameter and NAN_WEAK_CALLBACK. The callback has to be fully specialized to work on all versions of Node.

NAN_WEAK_CALLBACK(weakCallback) {

...

}

Local<Function> func;

...

int *parameter = new int(0);
NanMakeWeakPersistent(func, parameter, &weakCallback<Function, int>);

NanSetTemplate(templ, name, value)

Use to add properties on object and function templates.

NanMakeCallback(target, func, argc, argv)

Use instead of node::MakeCallback to call javascript functions. This is the only proper way of calling functions.

NanCompileScript(Handle s [, const ScriptOrigin& origin])

Use to create new scripts bound to the current context.

NanRunScript(script)

Use to run both bound and unbound scripts.

NanAdjustExternalMemory(int change_in_bytes)

Simply does AdjustAmountOfExternalAllocatedMemory

NanAddGCEpilogueCallback(GCEpilogueCallback callback, GCType gc_type_filter=kGCTypeAll)

Simply does AddGCEpilogueCallback

NanAddGCPrologueCallback(GCPrologueCallback callback, GCType gc_type_filter=kGCTypeAll)

Simply does AddGCPrologueCallback

NanRemoveGCEpilogueCallback(GCEpilogueCallback callback)

Simply does RemoveGCEpilogueCallback

NanRemoveGCPrologueCallback(GCPrologueCallback callback)

Simply does RemoveGCPrologueCallback

NanGetHeapStatistics(HeapStatistics *heap_statistics)

Simply does GetHeapStatistics

NanCallback

Because of the difficulties imposed by the changes to Persistent handles in V8 in Node 0.11, creating Persistent versions of your Handle<Function> is annoyingly tricky. NanCallback makes it easier by taking your handle, making it persistent until the NanCallback is deleted and even providing a handy Call() method to fetch and execute the callback Function.

Local<Function> callbackHandle = args[0].As<Function>();
NanCallback *callback = new NanCallback(callbackHandle);
// pass `callback` around and it's safe from GC until you:
delete callback;

You can execute the callback like so:

// no arguments:
callback->Call(0, NULL);

// an error argument:
Handle<Value> argv[] = {
  NanError(NanNew<String>("fail!"))
};
callback->Call(1, argv);

// a success argument:
Handle<Value> argv[] = {
  NanNull(),
  NanNew<String>("w00t!")
};
callback->Call(2, argv);

NanCallback also has a Local<Function> GetCallback() method that you can use to fetch a local handle to the underlying callback function, as well as a void SetFunction(Handle<Function>) for setting the callback on the NanCallback. You can check if a NanCallback is empty with the bool IsEmpty() method. Additionally a generic constructor is available for using NanCallback without performing heap allocations.

NanAsyncWorker

NanAsyncWorker is an abstract class that you can subclass to have much of the annoying async queuing and handling taken care of for you. It can even store arbitrary V8 objects for you and have them persist while the async work is in progress.

See a rough outline of the implementation:

class NanAsyncWorker {
public:
  NanAsyncWorker (NanCallback *callback);

  // Clean up persistent handles and delete the *callback
  virtual ~NanAsyncWorker ();

  // Check the `ErrorMessage()` and call HandleOKCallback()
  // or HandleErrorCallback depending on whether it has been set or not
  virtual void WorkComplete ();

  // You must implement this to do some async work. If there is an
  // error then use `SetErrorMessage()` to set an error message and the callback will
  // be passed that string in an Error object
  virtual void Execute ();

  // Save a V8 object in a Persistent handle to protect it from GC
  void SaveToPersistent(const char *key, Local<Object> &obj);

  // Fetch a stored V8 object (don't call from within `Execute()`)
  Local<Object> GetFromPersistent(const char *key);
  
  // Get the error message (or NULL)
  const char *ErrorMessage();
  
  // Set an error message
  void SetErrorMessage(const char *msg);
  
protected:
  // Default implementation calls the callback function with no arguments.
  // Override this to return meaningful data
  virtual void HandleOKCallback ();

  // Default implementation calls the callback function with an Error object
  // wrapping the `errmsg` string
  virtual void HandleErrorCallback ();
};

NanAsyncQueueWorker(NanAsyncWorker *)

NanAsyncQueueWorker will run a NanAsyncWorker asynchronously via libuv. Both the execute and after_work steps are taken care of for you—most of the logic for this is embedded in NanAsyncWorker.

Contributors

NAN is only possible due to the excellent work of the following contributors:

Rod VaggGitHub/rvaggTwitter/@rvagg
Benjamin ByholmGitHub/kkoopa-
Trevor NorrisGitHub/trevnorrisTwitter/@trevnorris
Nathan RajlichGitHub/TooTallNateTwitter/@TooTallNate
Brett LawsonGitHub/brett19Twitter/@brett19x
Ben NoordhuisGitHub/bnoordhuisTwitter/@bnoordhuis

Licence & copyright

Copyright (c) 2014 NAN contributors (listed above).

Native Abstractions for Node.js is licensed under an MIT +no-false-attribs license. All rights not explicitly granted in the MIT license are reserved. See the included LICENSE file for more details.