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<ul>
<li><a href="#addons_addons">Addons</a><ul>
<li><a href="#addons_hello_world">Hello world</a></li>
<li><a href="#addons_addon_patterns">Addon patterns</a><ul>
<li><a href="#addons_function_arguments">Function arguments</a></li>
<li><a href="#addons_callbacks">Callbacks</a></li>
<li><a href="#addons_object_factory">Object factory</a></li>
<li><a href="#addons_function_factory">Function factory</a></li>
<li><a href="#addons_wrapping_c_objects">Wrapping C++ objects</a></li>
<li><a href="#addons_factory_of_wrapped_objects">Factory of wrapped objects</a></li>
<li><a href="#addons_passing_wrapped_objects_around">Passing wrapped objects around</a></li>
<li><a href="#addons_atexit_hooks">AtExit hooks</a><ul>
<li><a href="#addons_void_atexit_callback_args">void AtExit(callback, args)</a></li>
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<div id="apicontent">
<h1>Addons<span><a class="mark" href="#addons_addons" id="addons_addons">#</a></span></h1>
<p>Addons are dynamically-linked shared objects. They can provide glue to C and
C++ libraries. The API (at the moment) is rather complex, involving
knowledge of several libraries:
</p>
<ul>
<li><p>V8 JavaScript, a C++ library. Used for interfacing with JavaScript:
creating objects, calling functions, etc. Documented mostly in the
<code>v8.h</code> header file (<code>deps/v8/include/v8.h</code> in the Node.js source
tree), which is also available <a href="https://v8docs.nodesource.com/">online</a>.</p>
</li>
<li><p><a href="https://github.com/libuv/libuv">libuv</a>, C event loop library. Anytime one needs to wait for a file
descriptor to become readable, wait for a timer, or wait for a signal
to be received, one will need to interface with libuv. That is, if you
perform any I/O, libuv will need to be used.</p>
</li>
<li><p>Internal Node.js libraries. The most important class is <code>node::ObjectWrap</code>
which you will likely want to derive from.</p>
</li>
<li><p>Others. Look in <code>deps/</code> for what else is available.</p>
</li>
</ul>
<p>Node.js statically compiles all its dependencies into the executable.
When compiling your module, you don't need to worry about linking to
any of these libraries.
</p>
<p>All of the following examples are available for <a href="https://github.com/nodejs/node-addon-examples">download</a> and may
be used as a starting-point for your own Addon.
</p>
<h2>Hello world<span><a class="mark" href="#addons_hello_world" id="addons_hello_world">#</a></span></h2>
<p>To get started, let's make a small Addon which is the C++ equivalent of
the following JavaScript code:
</p>
<pre><code>module.exports.hello = function() { return 'world'; };</code></pre>
<p>First we create a file <code>hello.cc</code>:
</p>
<pre><code>// hello.cc
#include <node.h>
namespace demo {
using v8::FunctionCallbackInfo;
using v8::Isolate;
using v8::Local;
using v8::Object;
using v8::String;
using v8::Value;
void Method(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
args.GetReturnValue().Set(String::NewFromUtf8(isolate, "world"));
}
void init(Local<Object> exports) {
NODE_SET_METHOD(exports, "hello", Method);
}
NODE_MODULE(addon, init)
} // namespace demo</code></pre>
<p>Note that all Node.js addons must export an initialization function:
</p>
<pre><code>void Initialize(Local<Object> exports);
NODE_MODULE(module_name, Initialize)</code></pre>
<p>There is no semi-colon after <code>NODE_MODULE</code> as it's not a function (see
<code>node.h</code>).
</p>
<p>The <code>module_name</code> needs to match the filename of the final binary (excluding
the .node suffix).
</p>
<p>The source code needs to be built into <code>addon.node</code>, the binary Addon. To
do this, we create a file called <code>binding.gyp</code> which describes the configuration
to build your module in a JSON-like format. This file gets compiled by
<a href="https://github.com/nodejs/node-gyp">node-gyp</a>.
</p>
<pre><code>{
"targets": [
{
"target_name": "addon",
"sources": [ "hello.cc" ]
}
]
}</code></pre>
<p>The next step is to generate the appropriate project build files for the
current platform. Use <code>node-gyp configure</code> for that.
</p>
<p>Now you will have either a <code>Makefile</code> (on Unix platforms) or a <code>vcxproj</code> file
(on Windows) in the <code>build/</code> directory. Next, invoke the <code>node-gyp build</code>
command.
</p>
<p>Now you have your compiled <code>.node</code> bindings file! The compiled bindings end up
in <code>build/Release/</code>.
</p>
<p>You can now use the binary addon in a Node.js project <code>hello.js</code> by pointing
<code>require</code> to the recently built <code>hello.node</code> module:
</p>
<pre><code>// hello.js
const addon = require('./build/Release/addon');
console.log(addon.hello()); // 'world'</code></pre>
<p>Please see patterns below for further information or
</p>
<p><a href="https://github.com/arturadib/node-qt">https://github.com/arturadib/node-qt</a> for an example in production.
</p>
<h2>Addon patterns<span><a class="mark" href="#addons_addon_patterns" id="addons_addon_patterns">#</a></span></h2>
<p>Below are some addon patterns to help you get started. Consult the online
<a href="http://izs.me/v8-docs/main.html">v8 reference</a> for help with the various v8 calls, and v8's
<a href="https://code.google.com/apis/v8/embed.html">Embedder's Guide</a> for an explanation of several concepts used such as
handles, scopes, function templates, etc.
</p>
<p>In order to use these examples, you need to compile them using <code>node-gyp</code>.
Create the following <code>binding.gyp</code> file:
</p>
<pre><code>{
"targets": [
{
"target_name": "addon",
"sources": [ "addon.cc" ]
}
]
}</code></pre>
<p>In cases where there is more than one <code>.cc</code> file, simply add the file name to
the <code>sources</code> array. For example:
</p>
<pre><code>"sources": ["addon.cc", "myexample.cc"]</code></pre>
<p>Now that you have your <code>binding.gyp</code> ready, you can configure and build the
addon:
</p>
<pre><code>$ node-gyp configure build</code></pre>
<h3>Function arguments<span><a class="mark" href="#addons_function_arguments" id="addons_function_arguments">#</a></span></h3>
<p>The following pattern illustrates how to read arguments from JavaScript
function calls and return a result. This is the main and only needed source
<code>addon.cc</code>:
</p>
<pre><code>// addon.cc
#include <node.h>
namespace demo {
using v8::Exception;
using v8::FunctionCallbackInfo;
using v8::Isolate;
using v8::Local;
using v8::Number;
using v8::Object;
using v8::String;
using v8::Value;
void Add(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
if (args.Length() < 2) {
isolate->ThrowException(Exception::TypeError(
String::NewFromUtf8(isolate, "Wrong number of arguments")));
return;
}
if (!args[0]->IsNumber() || !args[1]->IsNumber()) {
isolate->ThrowException(Exception::TypeError(
String::NewFromUtf8(isolate, "Wrong arguments")));
return;
}
double value = args[0]->NumberValue() + args[1]->NumberValue();
Local<Number> num = Number::New(isolate, value);
args.GetReturnValue().Set(num);
}
void Init(Local<Object> exports) {
NODE_SET_METHOD(exports, "add", Add);
}
NODE_MODULE(addon, Init)
} // namespace demo</code></pre>
<p>You can test it with the following JavaScript snippet:
</p>
<pre><code>// test.js
const addon = require('./build/Release/addon');
console.log( 'This should be eight:', addon.add(3,5) );</code></pre>
<h3>Callbacks<span><a class="mark" href="#addons_callbacks" id="addons_callbacks">#</a></span></h3>
<p>You can pass JavaScript functions to a C++ function and execute them from
there. Here's <code>addon.cc</code>:
</p>
<pre><code>// addon.cc
#include <node.h>
namespace demo {
using v8::Function;
using v8::FunctionCallbackInfo;
using v8::Isolate;
using v8::Local;
using v8::Null;
using v8::Object;
using v8::String;
using v8::Value;
void RunCallback(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
Local<Function> cb = Local<Function>::Cast(args[0]);
const unsigned argc = 1;
Local<Value> argv[argc] = { String::NewFromUtf8(isolate, "hello world") };
cb->Call(Null(isolate), argc, argv);
}
void Init(Local<Object> exports, Local<Object> module) {
NODE_SET_METHOD(module, "exports", RunCallback);
}
NODE_MODULE(addon, Init)
} // namespace demo</code></pre>
<p>Note that this example uses a two-argument form of <code>Init()</code> that receives
the full <code>module</code> object as the second argument. This allows the addon
to completely overwrite <code>exports</code> with a single function instead of
adding the function as a property of <code>exports</code>.
</p>
<p>To test it, run the following JavaScript snippet:
</p>
<pre><code>// test.js
const addon = require('./build/Release/addon');
addon(function(msg){
console.log(msg); // 'hello world'
});</code></pre>
<h3>Object factory<span><a class="mark" href="#addons_object_factory" id="addons_object_factory">#</a></span></h3>
<p>You can create and return new objects from within a C++ function with this
<code>addon.cc</code> pattern, which returns an object with property <code>msg</code> that echoes
the string passed to <code>createObject()</code>:
</p>
<pre><code>// addon.cc
#include <node.h>
namespace demo {
using v8::FunctionCallbackInfo;
using v8::Isolate;
using v8::Local;
using v8::Object;
using v8::String;
using v8::Value;
void CreateObject(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
Local<Object> obj = Object::New(isolate);
obj->Set(String::NewFromUtf8(isolate, "msg"), args[0]->ToString());
args.GetReturnValue().Set(obj);
}
void Init(Local<Object> exports, Local<Object> module) {
NODE_SET_METHOD(module, "exports", CreateObject);
}
NODE_MODULE(addon, Init)
} // namespace demo</code></pre>
<p>To test it in JavaScript:
</p>
<pre><code>// test.js
const addon = require('./build/Release/addon');
var obj1 = addon('hello');
var obj2 = addon('world');
console.log(obj1.msg+' '+obj2.msg); // 'hello world'</code></pre>
<h3>Function factory<span><a class="mark" href="#addons_function_factory" id="addons_function_factory">#</a></span></h3>
<p>This pattern illustrates how to create and return a JavaScript function that
wraps a C++ function:
</p>
<pre><code>// addon.cc
#include <node.h>
namespace demo {
using v8::Function;
using v8::FunctionCallbackInfo;
using v8::FunctionTemplate;
using v8::Isolate;
using v8::Local;
using v8::Object;
using v8::String;
using v8::Value;
void MyFunction(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
args.GetReturnValue().Set(String::NewFromUtf8(isolate, "hello world"));
}
void CreateFunction(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
Local<FunctionTemplate> tpl = FunctionTemplate::New(isolate, MyFunction);
Local<Function> fn = tpl->GetFunction();
// omit this to make it anonymous
fn->SetName(String::NewFromUtf8(isolate, "theFunction"));
args.GetReturnValue().Set(fn);
}
void Init(Local<Object> exports, Local<Object> module) {
NODE_SET_METHOD(module, "exports", CreateFunction);
}
NODE_MODULE(addon, Init)
} // namespace demo</code></pre>
<p>To test:
</p>
<pre><code>// test.js
const addon = require('./build/Release/addon');
var fn = addon();
console.log(fn()); // 'hello world'</code></pre>
<h3>Wrapping C++ objects<span><a class="mark" href="#addons_wrapping_c_objects" id="addons_wrapping_c_objects">#</a></span></h3>
<p>Here, we will create a wrapper for a C++ object/class <code>MyObject</code> that can be
instantiated in JavaScript through the <code>new</code> operator. First, prepare the main
module <code>addon.cc</code>:
</p>
<pre><code>// addon.cc
#include <node.h>
#include "myobject.h"
namespace demo {
using v8::Local;
using v8::Object;
void InitAll(Local<Object> exports) {
MyObject::Init(exports);
}
NODE_MODULE(addon, InitAll)
} // namespace demo</code></pre>
<p>Then, in <code>myobject.h</code>, make your wrapper inherit from <code>node::ObjectWrap</code>:
</p>
<pre><code>// myobject.h
#ifndef MYOBJECT_H
#define MYOBJECT_H
#include <node.h>
#include <node_object_wrap.h>
namespace demo {
class MyObject : public node::ObjectWrap {
public:
static void Init(v8::Local<v8::Object> exports);
private:
explicit MyObject(double value = 0);
~MyObject();
static void New(const v8::FunctionCallbackInfo<v8::Value>& args);
static void PlusOne(const v8::FunctionCallbackInfo<v8::Value>& args);
static v8::Persistent<v8::Function> constructor;
double value_;
};
} // namespace demo
#endif</code></pre>
<p>And in <code>myobject.cc</code>, implement the various methods that you want to expose.
Here we expose the method <code>plusOne</code> by adding it to the constructor's
prototype:
</p>
<pre><code>// myobject.cc
#include "myobject.h"
namespace demo {
using v8::Function;
using v8::FunctionCallbackInfo;
using v8::FunctionTemplate;
using v8::Isolate;
using v8::Local;
using v8::Number;
using v8::Object;
using v8::Persistent;
using v8::String;
using v8::Value;
Persistent<Function> MyObject::constructor;
MyObject::MyObject(double value) : value_(value) {
}
MyObject::~MyObject() {
}
void MyObject::Init(Local<Object> exports) {
Isolate* isolate = exports->GetIsolate();
// Prepare constructor template
Local<FunctionTemplate> tpl = FunctionTemplate::New(isolate, New);
tpl->SetClassName(String::NewFromUtf8(isolate, "MyObject"));
tpl->InstanceTemplate()->SetInternalFieldCount(1);
// Prototype
NODE_SET_PROTOTYPE_METHOD(tpl, "plusOne", PlusOne);
constructor.Reset(isolate, tpl->GetFunction());
exports->Set(String::NewFromUtf8(isolate, "MyObject"),
tpl->GetFunction());
}
void MyObject::New(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
if (args.IsConstructCall()) {
// Invoked as constructor: `new MyObject(...)`
double value = args[0]->IsUndefined() ? 0 : args[0]->NumberValue();
MyObject* obj = new MyObject(value);
obj->Wrap(args.This());
args.GetReturnValue().Set(args.This());
} else {
// Invoked as plain function `MyObject(...)`, turn into construct call.
const int argc = 1;
Local<Value> argv[argc] = { args[0] };
Local<Function> cons = Local<Function>::New(isolate, constructor);
args.GetReturnValue().Set(cons->NewInstance(argc, argv));
}
}
void MyObject::PlusOne(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
MyObject* obj = ObjectWrap::Unwrap<MyObject>(args.Holder());
obj->value_ += 1;
args.GetReturnValue().Set(Number::New(isolate, obj->value_));
}
} // namespace demo</code></pre>
<p>Test it with:
</p>
<pre><code>// test.js
const addon = require('./build/Release/addon');
var obj = new addon.MyObject(10);
console.log( obj.plusOne() ); // 11
console.log( obj.plusOne() ); // 12
console.log( obj.plusOne() ); // 13</code></pre>
<h3>Factory of wrapped objects<span><a class="mark" href="#addons_factory_of_wrapped_objects" id="addons_factory_of_wrapped_objects">#</a></span></h3>
<p>This is useful when you want to be able to create native objects without
explicitly instantiating them with the <code>new</code> operator in JavaScript. For
example:
</p>
<pre><code>var obj = addon.createObject();
// instead of:
// var obj = new addon.Object();</code></pre>
<p>Let's register our <code>createObject</code> method in <code>addon.cc</code>:
</p>
<pre><code>// addon.cc
#include <node.h>
#include "myobject.h"
namespace demo {
using v8::FunctionCallbackInfo;
using v8::Isolate;
using v8::Local;
using v8::Object;
using v8::String;
using v8::Value;
void CreateObject(const FunctionCallbackInfo<Value>& args) {
MyObject::NewInstance(args);
}
void InitAll(Local<Object> exports, Local<Object> module) {
MyObject::Init(exports->GetIsolate());
NODE_SET_METHOD(module, "exports", CreateObject);
}
NODE_MODULE(addon, InitAll)
} // namespace demo</code></pre>
<p>In <code>myobject.h</code>, we now introduce the static method <code>NewInstance</code> that takes
care of instantiating the object. In other words, it does the job of <code>new</code> in
JavaScript:
</p>
<pre><code>// myobject.h
#ifndef MYOBJECT_H
#define MYOBJECT_H
#include <node.h>
#include <node_object_wrap.h>
namespace demo {
class MyObject : public node::ObjectWrap {
public:
static void Init(v8::Isolate* isolate);
static void NewInstance(const v8::FunctionCallbackInfo<v8::Value>& args);
private:
explicit MyObject(double value = 0);
~MyObject();
static void New(const v8::FunctionCallbackInfo<v8::Value>& args);
static void PlusOne(const v8::FunctionCallbackInfo<v8::Value>& args);
static v8::Persistent<v8::Function> constructor;
double value_;
};
} // namespace demo
#endif</code></pre>
<p>The implementation is similar to the above in <code>myobject.cc</code>:
</p>
<pre><code>// myobject.cc
#include <node.h>
#include "myobject.h"
namespace demo {
using v8::Function;
using v8::FunctionCallbackInfo;
using v8::FunctionTemplate;
using v8::Isolate;
using v8::Local;
using v8::Number;
using v8::Object;
using v8::Persistent;
using v8::String;
using v8::Value;
Persistent<Function> MyObject::constructor;
MyObject::MyObject(double value) : value_(value) {
}
MyObject::~MyObject() {
}
void MyObject::Init(Isolate* isolate) {
// Prepare constructor template
Local<FunctionTemplate> tpl = FunctionTemplate::New(isolate, New);
tpl->SetClassName(String::NewFromUtf8(isolate, "MyObject"));
tpl->InstanceTemplate()->SetInternalFieldCount(1);
// Prototype
NODE_SET_PROTOTYPE_METHOD(tpl, "plusOne", PlusOne);
constructor.Reset(isolate, tpl->GetFunction());
}
void MyObject::New(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
if (args.IsConstructCall()) {
// Invoked as constructor: `new MyObject(...)`
double value = args[0]->IsUndefined() ? 0 : args[0]->NumberValue();
MyObject* obj = new MyObject(value);
obj->Wrap(args.This());
args.GetReturnValue().Set(args.This());
} else {
// Invoked as plain function `MyObject(...)`, turn into construct call.
const int argc = 1;
Local<Value> argv[argc] = { args[0] };
Local<Function> cons = Local<Function>::New(isolate, constructor);
args.GetReturnValue().Set(cons->NewInstance(argc, argv));
}
}
void MyObject::NewInstance(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
const unsigned argc = 1;
Local<Value> argv[argc] = { args[0] };
Local<Function> cons = Local<Function>::New(isolate, constructor);
Local<Object> instance = cons->NewInstance(argc, argv);
args.GetReturnValue().Set(instance);
}
void MyObject::PlusOne(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
MyObject* obj = ObjectWrap::Unwrap<MyObject>(args.Holder());
obj->value_ += 1;
args.GetReturnValue().Set(Number::New(isolate, obj->value_));
}
} // namespace demo</code></pre>
<p>Test it with:
</p>
<pre><code>// test.js
const createObject = require('./build/Release/addon');
var obj = createObject(10);
console.log( obj.plusOne() ); // 11
console.log( obj.plusOne() ); // 12
console.log( obj.plusOne() ); // 13
var obj2 = createObject(20);
console.log( obj2.plusOne() ); // 21
console.log( obj2.plusOne() ); // 22
console.log( obj2.plusOne() ); // 23</code></pre>
<h3>Passing wrapped objects around<span><a class="mark" href="#addons_passing_wrapped_objects_around" id="addons_passing_wrapped_objects_around">#</a></span></h3>
<p>In addition to wrapping and returning C++ objects, you can pass them around
by unwrapping them with the Node.js helper function <code>node::ObjectWrap::Unwrap</code>.
In the following <code>addon.cc</code>, we introduce a function <code>add()</code> that can take on
two <code>MyObject</code> objects:
</p>
<pre><code>// addon.cc
#include <node.h>
#include <node_object_wrap.h>
#include "myobject.h"
namespace demo {
using v8::FunctionCallbackInfo;
using v8::Isolate;
using v8::Local;
using v8::Number;
using v8::Object;
using v8::String;
using v8::Value;
void CreateObject(const FunctionCallbackInfo<Value>& args) {
MyObject::NewInstance(args);
}
void Add(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
MyObject* obj1 = node::ObjectWrap::Unwrap<MyObject>(
args[0]->ToObject());
MyObject* obj2 = node::ObjectWrap::Unwrap<MyObject>(
args[1]->ToObject());
double sum = obj1->value() + obj2->value();
args.GetReturnValue().Set(Number::New(isolate, sum));
}
void InitAll(Local<Object> exports) {
MyObject::Init(exports->GetIsolate());
NODE_SET_METHOD(exports, "createObject", CreateObject);
NODE_SET_METHOD(exports, "add", Add);
}
NODE_MODULE(addon, InitAll)
} // namespace demo</code></pre>
<p>To make things interesting, we introduce a public method in <code>myobject.h</code> so we
can probe private values after unwrapping the object:
</p>
<pre><code>// myobject.h
#ifndef MYOBJECT_H
#define MYOBJECT_H
#include <node.h>
#include <node_object_wrap.h>
namespace demo {
class MyObject : public node::ObjectWrap {
public:
static void Init(v8::Isolate* isolate);
static void NewInstance(const v8::FunctionCallbackInfo<v8::Value>& args);
inline double value() const { return value_; }
private:
explicit MyObject(double value = 0);
~MyObject();
static void New(const v8::FunctionCallbackInfo<v8::Value>& args);
static v8::Persistent<v8::Function> constructor;
double value_;
};
} // namespace demo
#endif</code></pre>
<p>The implementation of <code>myobject.cc</code> is similar to before:
</p>
<pre><code>// myobject.cc
#include <node.h>
#include "myobject.h"
namespace demo {
using v8::Function;
using v8::FunctionCallbackInfo;
using v8::FunctionTemplate;
using v8::Isolate;
using v8::Local;
using v8::Object;
using v8::Persistent;
using v8::String;
using v8::Value;
Persistent<Function> MyObject::constructor;
MyObject::MyObject(double value) : value_(value) {
}
MyObject::~MyObject() {
}
void MyObject::Init(Isolate* isolate) {
// Prepare constructor template
Local<FunctionTemplate> tpl = FunctionTemplate::New(isolate, New);
tpl->SetClassName(String::NewFromUtf8(isolate, "MyObject"));
tpl->InstanceTemplate()->SetInternalFieldCount(1);
constructor.Reset(isolate, tpl->GetFunction());
}
void MyObject::New(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
if (args.IsConstructCall()) {
// Invoked as constructor: `new MyObject(...)`
double value = args[0]->IsUndefined() ? 0 : args[0]->NumberValue();
MyObject* obj = new MyObject(value);
obj->Wrap(args.This());
args.GetReturnValue().Set(args.This());
} else {
// Invoked as plain function `MyObject(...)`, turn into construct call.
const int argc = 1;
Local<Value> argv[argc] = { args[0] };
Local<Function> cons = Local<Function>::New(isolate, constructor);
args.GetReturnValue().Set(cons->NewInstance(argc, argv));
}
}
void MyObject::NewInstance(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
const unsigned argc = 1;
Local<Value> argv[argc] = { args[0] };
Local<Function> cons = Local<Function>::New(isolate, constructor);
Local<Object> instance = cons->NewInstance(argc, argv);
args.GetReturnValue().Set(instance);
}
} // namespace demo</code></pre>
<p>Test it with:
</p>
<pre><code>// test.js
const addon = require('./build/Release/addon');
var obj1 = addon.createObject(10);
var obj2 = addon.createObject(20);
var result = addon.add(obj1, obj2);
console.log(result); // 30</code></pre>
<h3>AtExit hooks<span><a class="mark" href="#addons_atexit_hooks" id="addons_atexit_hooks">#</a></span></h3>
<h4>void AtExit(callback, args)<span><a class="mark" href="#addons_void_atexit_callback_args" id="addons_void_atexit_callback_args">#</a></span></h4>
<ul>
<li><code>callback</code>: <code>void (*)(void*)</code> - A pointer to the function to call at exit.</li>
<li><code>args</code>: <code>void*</code> - A pointer to pass to the callback at exit.</li>
</ul>
<p>Registers exit hooks that run after the event loop has ended but before the VM
is killed.
</p>
<p>Callbacks are run in last-in first-out order. AtExit takes two parameters:
a pointer to a callback function to run at exit, and a pointer to untyped
context data to be passed to that callback.
</p>
<p>The file <code>addon.cc</code> implements AtExit below:
</p>
<pre><code>// addon.cc
#undef NDEBUG
#include <assert.h>
#include <stdlib.h>
#include <node.h>
namespace demo {
using node::AtExit;
using v8::HandleScope;
using v8::Isolate;
using v8::Local;
using v8::Object;
static char cookie[] = "yum yum";
static int at_exit_cb1_called = 0;
static int at_exit_cb2_called = 0;
static void at_exit_cb1(void* arg) {
Isolate* isolate = static_cast<Isolate*>(arg);
HandleScope scope(isolate);
Local<Object> obj = Object::New(isolate);
assert(!obj.IsEmpty()); // assert VM is still alive
assert(obj->IsObject());
at_exit_cb1_called++;
}
static void at_exit_cb2(void* arg) {
assert(arg == static_cast<void*>(cookie));
at_exit_cb2_called++;
}
static void sanity_check(void*) {
assert(at_exit_cb1_called == 1);
assert(at_exit_cb2_called == 2);
}
void init(Local<Object> exports) {
AtExit(sanity_check);
AtExit(at_exit_cb2, cookie);
AtExit(at_exit_cb2, cookie);
AtExit(at_exit_cb1, exports->GetIsolate());
}
NODE_MODULE(addon, init);
} // namespace demo</code></pre>
<p>Test in JavaScript by running:
</p>
<pre><code>// test.js
const addon = require('./build/Release/addon');</code></pre>
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