{ "source": "doc/api/addons.markdown", "modules": [ { "textRaw": "Addons", "name": "addons", "desc": "

Addons are dynamically linked shared objects. They can provide glue to C and\nC++ libraries. The API (at the moment) is rather complex, involving\nknowledge of several libraries:\n\n

\n\n

Node statically compiles all its dependencies into the executable.\nWhen compiling your module, you don't need to worry about linking to\nany of these libraries.\n\n

\n

All of the following examples are available for\ndownload and may be\nused as a starting-point for your own Addon.\n\n

\n", "modules": [ { "textRaw": "Hello world", "name": "hello_world", "desc": "

To get started let's make a small Addon which is the C++ equivalent of\nthe following JavaScript code:\n\n

\n
module.exports.hello = function() { return 'world'; };
\n

First we create a file hello.cc:\n\n

\n
// hello.cc\n#include <node.h>\n\nusing namespace v8;\n\nvoid Method(const FunctionCallbackInfo<Value>& args) {\n  Isolate* isolate = Isolate::GetCurrent();\n  HandleScope scope(isolate);\n  args.GetReturnValue().Set(String::NewFromUtf8(isolate, "world"));\n}\n\nvoid init(Handle<Object> exports) {\n  NODE_SET_METHOD(exports, "hello", Method);\n}\n\nNODE_MODULE(addon, init)
\n

Note that all Node addons must export an initialization function:\n\n

\n
void Initialize (Handle<Object> exports);\nNODE_MODULE(module_name, Initialize)
\n

There is no semi-colon after NODE_MODULE as it's not a function (see\nnode.h).\n\n

\n

The module_name needs to match the filename of the final binary (minus the\n.node suffix).\n\n

\n

The source code needs to be built into addon.node, the binary Addon. To\ndo this we create a file called binding.gyp which describes the configuration\nto build your module in a JSON-like format. This file gets compiled by\nnode-gyp.\n\n

\n
{\n  "targets": [\n    {\n      "target_name": "addon",\n      "sources": [ "hello.cc" ]\n    }\n  ]\n}
\n

The next step is to generate the appropriate project build files for the\ncurrent platform. Use node-gyp configure for that.\n\n

\n

Now you will have either a Makefile (on Unix platforms) or a vcxproj file\n(on Windows) in the build/ directory. Next invoke the node-gyp build\ncommand.\n\n

\n

Now you have your compiled .node bindings file! The compiled bindings end up\nin build/Release/.\n\n

\n

You can now use the binary addon in a Node project hello.js by pointing\nrequire to the recently built hello.node module:\n\n

\n
// hello.js\nvar addon = require('./build/Release/addon');\n\nconsole.log(addon.hello()); // 'world'
\n

Please see patterns below for further information or\n

\n

https://github.com/arturadib/node-qt for an example in production.\n\n\n

\n", "type": "module", "displayName": "Hello world" }, { "textRaw": "Addon patterns", "name": "addon_patterns", "desc": "

Below are some addon patterns to help you get started. Consult the online\nv8 reference for help with the various v8\ncalls, and v8's Embedder's Guide\nfor an explanation of several concepts used such as handles, scopes,\nfunction templates, etc.\n\n

\n

In order to use these examples you need to compile them using node-gyp.\nCreate the following binding.gyp file:\n\n

\n
{\n  "targets": [\n    {\n      "target_name": "addon",\n      "sources": [ "addon.cc" ]\n    }\n  ]\n}
\n

In cases where there is more than one .cc file, simply add the file name to\nthe sources array, e.g.:\n\n

\n
"sources": ["addon.cc", "myexample.cc"]
\n

Now that you have your binding.gyp ready, you can configure and build the\naddon:\n\n

\n
$ node-gyp configure build
\n", "modules": [ { "textRaw": "Function arguments", "name": "function_arguments", "desc": "

The following pattern illustrates how to read arguments from JavaScript\nfunction calls and return a result. This is the main and only needed source\naddon.cc:\n\n

\n
// addon.cc\n#include <node.h>\n\nusing namespace v8;\n\nvoid Add(const FunctionCallbackInfo<Value>& args) {\n  Isolate* isolate = Isolate::GetCurrent();\n  HandleScope scope(isolate);\n\n  if (args.Length() < 2) {\n    isolate->ThrowException(Exception::TypeError(\n        String::NewFromUtf8(isolate, "Wrong number of arguments")));\n    return;\n  }\n\n  if (!args[0]->IsNumber() || !args[1]->IsNumber()) {\n    isolate->ThrowException(Exception::TypeError(\n        String::NewFromUtf8(isolate, "Wrong arguments")));\n    return;\n  }\n\n  double value = args[0]->NumberValue() + args[1]->NumberValue();\n  Local<Number> num = Number::New(isolate, value);\n\n  args.GetReturnValue().Set(num);\n}\n\nvoid Init(Handle<Object> exports) {\n  NODE_SET_METHOD(exports, "add", Add);\n}\n\nNODE_MODULE(addon, Init)
\n

You can test it with the following JavaScript snippet:\n\n

\n
// test.js\nvar addon = require('./build/Release/addon');\n\nconsole.log( 'This should be eight:', addon.add(3,5) );
\n", "type": "module", "displayName": "Function arguments" }, { "textRaw": "Callbacks", "name": "callbacks", "desc": "

You can pass JavaScript functions to a C++ function and execute them from\nthere. Here's addon.cc:\n\n

\n
// addon.cc\n#include <node.h>\n\nusing namespace v8;\n\nvoid RunCallback(const FunctionCallbackInfo<Value>& args) {\n  Isolate* isolate = Isolate::GetCurrent();\n  HandleScope scope(isolate);\n\n  Local<Function> cb = Local<Function>::Cast(args[0]);\n  const unsigned argc = 1;\n  Local<Value> argv[argc] = { String::NewFromUtf8(isolate, "hello world") };\n  cb->Call(isolate->GetCurrentContext()->Global(), argc, argv);\n}\n\nvoid Init(Handle<Object> exports, Handle<Object> module) {\n  NODE_SET_METHOD(module, "exports", RunCallback);\n}\n\nNODE_MODULE(addon, Init)
\n

Note that this example uses a two-argument form of Init() that receives\nthe full module object as the second argument. This allows the addon\nto completely overwrite exports with a single function instead of\nadding the function as a property of exports.\n\n

\n

To test it run the following JavaScript snippet:\n\n

\n
// test.js\nvar addon = require('./build/Release/addon');\n\naddon(function(msg){\n  console.log(msg); // 'hello world'\n});
\n", "type": "module", "displayName": "Callbacks" }, { "textRaw": "Object factory", "name": "object_factory", "desc": "

You can create and return new objects from within a C++ function with this\naddon.cc pattern, which returns an object with property msg that echoes\nthe string passed to createObject():\n\n

\n
// addon.cc\n#include <node.h>\n\nusing namespace v8;\n\nvoid CreateObject(const FunctionCallbackInfo<Value>& args) {\n  Isolate* isolate = Isolate::GetCurrent();\n  HandleScope scope(isolate);\n\n  Local<Object> obj = Object::New(isolate);\n  obj->Set(String::NewFromUtf8(isolate, "msg"), args[0]->ToString());\n\n  args.GetReturnValue().Set(obj);\n}\n\nvoid Init(Handle<Object> exports, Handle<Object> module) {\n  NODE_SET_METHOD(module, "exports", CreateObject);\n}\n\nNODE_MODULE(addon, Init)
\n

To test it in JavaScript:\n\n

\n
// test.js\nvar addon = require('./build/Release/addon');\n\nvar obj1 = addon('hello');\nvar obj2 = addon('world');\nconsole.log(obj1.msg+' '+obj2.msg); // 'hello world'
\n", "type": "module", "displayName": "Object factory" }, { "textRaw": "Function factory", "name": "function_factory", "desc": "

This pattern illustrates how to create and return a JavaScript function that\nwraps a C++ function:\n\n

\n
// addon.cc\n#include <node.h>\n\nusing namespace v8;\n\nvoid MyFunction(const FunctionCallbackInfo<Value>& args) {\n  Isolate* isolate = Isolate::GetCurrent();\n  HandleScope scope(isolate);\n  args.GetReturnValue().Set(String::NewFromUtf8(isolate, "hello world"));\n}\n\nvoid CreateFunction(const FunctionCallbackInfo<Value>& args) {\n  Isolate* isolate = Isolate::GetCurrent();\n  HandleScope scope(isolate);\n\n  Local<FunctionTemplate> tpl = FunctionTemplate::New(isolate, MyFunction);\n  Local<Function> fn = tpl->GetFunction();\n\n  // omit this to make it anonymous\n  fn->SetName(String::NewFromUtf8(isolate, "theFunction"));\n\n  args.GetReturnValue().Set(fn);\n}\n\nvoid Init(Handle<Object> exports, Handle<Object> module) {\n  NODE_SET_METHOD(module, "exports", CreateFunction);\n}\n\nNODE_MODULE(addon, Init)
\n

To test:\n\n

\n
// test.js\nvar addon = require('./build/Release/addon');\n\nvar fn = addon();\nconsole.log(fn()); // 'hello world'
\n", "type": "module", "displayName": "Function factory" }, { "textRaw": "Wrapping C++ objects", "name": "wrapping_c++_objects", "desc": "

Here we will create a wrapper for a C++ object/class MyObject that can be\ninstantiated in JavaScript through the new operator. First prepare the main\nmodule addon.cc:\n\n

\n
// addon.cc\n#include <node.h>\n#include "myobject.h"\n\nusing namespace v8;\n\nvoid InitAll(Handle<Object> exports) {\n  MyObject::Init(exports);\n}\n\nNODE_MODULE(addon, InitAll)
\n

Then in myobject.h make your wrapper inherit from node::ObjectWrap:\n\n

\n
// myobject.h\n#ifndef MYOBJECT_H\n#define MYOBJECT_H\n\n#include <node.h>\n#include <node_object_wrap.h>\n\nclass MyObject : public node::ObjectWrap {\n public:\n  static void Init(v8::Handle<v8::Object> exports);\n\n private:\n  explicit MyObject(double value = 0);\n  ~MyObject();\n\n  static void New(const v8::FunctionCallbackInfo<v8::Value>& args);\n  static void PlusOne(const v8::FunctionCallbackInfo<v8::Value>& args);\n  static v8::Persistent<v8::Function> constructor;\n  double value_;\n};\n\n#endif
\n

And in myobject.cc implement the various methods that you want to expose.\nHere we expose the method plusOne by adding it to the constructor's\nprototype:\n\n

\n
// myobject.cc\n#include "myobject.h"\n\nusing namespace v8;\n\nPersistent<Function> MyObject::constructor;\n\nMyObject::MyObject(double value) : value_(value) {\n}\n\nMyObject::~MyObject() {\n}\n\nvoid MyObject::Init(Handle<Object> exports) {\n  Isolate* isolate = Isolate::GetCurrent();\n\n  // Prepare constructor template\n  Local<FunctionTemplate> tpl = FunctionTemplate::New(isolate, New);\n  tpl->SetClassName(String::NewFromUtf8(isolate, "MyObject"));\n  tpl->InstanceTemplate()->SetInternalFieldCount(1);\n\n  // Prototype\n  NODE_SET_PROTOTYPE_METHOD(tpl, "plusOne", PlusOne);\n\n  constructor.Reset(isolate, tpl->GetFunction());\n  exports->Set(String::NewFromUtf8(isolate, "MyObject"),\n               tpl->GetFunction());\n}\n\nvoid MyObject::New(const FunctionCallbackInfo<Value>& args) {\n  Isolate* isolate = Isolate::GetCurrent();\n  HandleScope scope(isolate);\n\n  if (args.IsConstructCall()) {\n    // Invoked as constructor: `new MyObject(...)`\n    double value = args[0]->IsUndefined() ? 0 : args[0]->NumberValue();\n    MyObject* obj = new MyObject(value);\n    obj->Wrap(args.This());\n    args.GetReturnValue().Set(args.This());\n  } else {\n    // Invoked as plain function `MyObject(...)`, turn into construct call.\n    const int argc = 1;\n    Local<Value> argv[argc] = { args[0] };\n    Local<Function> cons = Local<Function>::New(isolate, constructor);\n    args.GetReturnValue().Set(cons->NewInstance(argc, argv));\n  }\n}\n\nvoid MyObject::PlusOne(const FunctionCallbackInfo<Value>& args) {\n  Isolate* isolate = Isolate::GetCurrent();\n  HandleScope scope(isolate);\n\n  MyObject* obj = ObjectWrap::Unwrap<MyObject>(args.Holder());\n  obj->value_ += 1;\n\n  args.GetReturnValue().Set(Number::New(isolate, obj->value_));\n}
\n

Test it with:\n\n

\n
// test.js\nvar addon = require('./build/Release/addon');\n\nvar obj = new addon.MyObject(10);\nconsole.log( obj.plusOne() ); // 11\nconsole.log( obj.plusOne() ); // 12\nconsole.log( obj.plusOne() ); // 13
\n", "type": "module", "displayName": "Wrapping C++ objects" }, { "textRaw": "Factory of wrapped objects", "name": "factory_of_wrapped_objects", "desc": "

This is useful when you want to be able to create native objects without\nexplicitly instantiating them with the new operator in JavaScript, e.g.\n\n

\n
var obj = addon.createObject();\n// instead of:\n// var obj = new addon.Object();
\n

Let's register our createObject method in addon.cc:\n\n

\n
// addon.cc\n#include <node.h>\n#include "myobject.h"\n\nusing namespace v8;\n\nvoid CreateObject(const FunctionCallbackInfo<Value>& args) {\n  Isolate* isolate = Isolate::GetCurrent();\n  HandleScope scope(isolate);\n  MyObject::NewInstance(args);\n}\n\nvoid InitAll(Handle<Object> exports, Handle<Object> module) {\n  MyObject::Init();\n\n  NODE_SET_METHOD(module, "exports", CreateObject);\n}\n\nNODE_MODULE(addon, InitAll)
\n

In myobject.h we now introduce the static method NewInstance that takes\ncare of instantiating the object (i.e. it does the job of new in JavaScript):\n\n

\n
// myobject.h\n#ifndef MYOBJECT_H\n#define MYOBJECT_H\n\n#include <node.h>\n#include <node_object_wrap.h>\n\nclass MyObject : public node::ObjectWrap {\n public:\n  static void Init();\n  static void NewInstance(const v8::FunctionCallbackInfo<v8::Value>& args);\n\n private:\n  explicit MyObject(double value = 0);\n  ~MyObject();\n\n  static void New(const v8::FunctionCallbackInfo<v8::Value>& args);\n  static void PlusOne(const v8::FunctionCallbackInfo<v8::Value>& args);\n  static v8::Persistent<v8::Function> constructor;\n  double value_;\n};\n\n#endif
\n

The implementation is similar to the above in myobject.cc:\n\n

\n
// myobject.cc\n#include <node.h>\n#include "myobject.h"\n\nusing namespace v8;\n\nPersistent<Function> MyObject::constructor;\n\nMyObject::MyObject(double value) : value_(value) {\n}\n\nMyObject::~MyObject() {\n}\n\nvoid MyObject::Init() {\n  Isolate* isolate = Isolate::GetCurrent();\n  // Prepare constructor template\n  Local<FunctionTemplate> tpl = FunctionTemplate::New(isolate, New);\n  tpl->SetClassName(String::NewFromUtf8(isolate, "MyObject"));\n  tpl->InstanceTemplate()->SetInternalFieldCount(1);\n\n  // Prototype\n  NODE_SET_PROTOTYPE_METHOD(tpl, "plusOne", PlusOne);\n\n  constructor.Reset(isolate, tpl->GetFunction());\n}\n\nvoid MyObject::New(const FunctionCallbackInfo<Value>& args) {\n  Isolate* isolate = Isolate::GetCurrent();\n  HandleScope scope(isolate);\n\n  if (args.IsConstructCall()) {\n    // Invoked as constructor: `new MyObject(...)`\n    double value = args[0]->IsUndefined() ? 0 : args[0]->NumberValue();\n    MyObject* obj = new MyObject(value);\n    obj->Wrap(args.This());\n    args.GetReturnValue().Set(args.This());\n  } else {\n    // Invoked as plain function `MyObject(...)`, turn into construct call.\n    const int argc = 1;\n    Local<Value> argv[argc] = { args[0] };\n    Local<Function> cons = Local<Function>::New(isolate, constructor);\n    args.GetReturnValue().Set(cons->NewInstance(argc, argv));\n  }\n}\n\nvoid MyObject::NewInstance(const FunctionCallbackInfo<Value>& args) {\n  Isolate* isolate = Isolate::GetCurrent();\n  HandleScope scope(isolate);\n\n  const unsigned argc = 1;\n  Handle<Value> argv[argc] = { args[0] };\n  Local<Function> cons = Local<Function>::New(isolate, constructor);\n  Local<Object> instance = cons->NewInstance(argc, argv);\n\n  args.GetReturnValue().Set(instance);\n}\n\nvoid MyObject::PlusOne(const FunctionCallbackInfo<Value>& args) {\n  Isolate* isolate = Isolate::GetCurrent();\n  HandleScope scope(isolate);\n\n  MyObject* obj = ObjectWrap::Unwrap<MyObject>(args.Holder());\n  obj->value_ += 1;\n\n  args.GetReturnValue().Set(Number::New(isolate, obj->value_));\n}
\n

Test it with:\n\n

\n
// test.js\nvar createObject = require('./build/Release/addon');\n\nvar obj = createObject(10);\nconsole.log( obj.plusOne() ); // 11\nconsole.log( obj.plusOne() ); // 12\nconsole.log( obj.plusOne() ); // 13\n\nvar obj2 = createObject(20);\nconsole.log( obj2.plusOne() ); // 21\nconsole.log( obj2.plusOne() ); // 22\nconsole.log( obj2.plusOne() ); // 23
\n", "type": "module", "displayName": "Factory of wrapped objects" }, { "textRaw": "Passing wrapped objects around", "name": "passing_wrapped_objects_around", "desc": "

In addition to wrapping and returning C++ objects, you can pass them around\nby unwrapping them with Node's node::ObjectWrap::Unwrap helper function.\nIn the following addon.cc we introduce a function add() that can take on two\nMyObject objects:\n\n

\n
// addon.cc\n#include <node.h>\n#include <node_object_wrap.h>\n#include "myobject.h"\n\nusing namespace v8;\n\nvoid CreateObject(const FunctionCallbackInfo<Value>& args) {\n  Isolate* isolate = Isolate::GetCurrent();\n  HandleScope scope(isolate);\n  MyObject::NewInstance(args);\n}\n\nvoid Add(const FunctionCallbackInfo<Value>& args) {\n  Isolate* isolate = Isolate::GetCurrent();\n  HandleScope scope(isolate);\n\n  MyObject* obj1 = node::ObjectWrap::Unwrap<MyObject>(\n      args[0]->ToObject());\n  MyObject* obj2 = node::ObjectWrap::Unwrap<MyObject>(\n      args[1]->ToObject());\n\n  double sum = obj1->value() + obj2->value();\n  args.GetReturnValue().Set(Number::New(isolate, sum));\n}\n\nvoid InitAll(Handle<Object> exports) {\n  MyObject::Init();\n\n  NODE_SET_METHOD(exports, "createObject", CreateObject);\n  NODE_SET_METHOD(exports, "add", Add);\n}\n\nNODE_MODULE(addon, InitAll)
\n

To make things interesting we introduce a public method in myobject.h so we\ncan probe private values after unwrapping the object:\n\n

\n
// myobject.h\n#ifndef MYOBJECT_H\n#define MYOBJECT_H\n\n#include <node.h>\n#include <node_object_wrap.h>\n\nclass MyObject : public node::ObjectWrap {\n public:\n  static void Init();\n  static void NewInstance(const v8::FunctionCallbackInfo<v8::Value>& args);\n  inline double value() const { return value_; }\n\n private:\n  explicit MyObject(double value = 0);\n  ~MyObject();\n\n  static void New(const v8::FunctionCallbackInfo<v8::Value>& args);\n  static v8::Persistent<v8::Function> constructor;\n  double value_;\n};\n\n#endif
\n

The implementation of myobject.cc is similar as before:\n\n

\n
// myobject.cc\n#include <node.h>\n#include "myobject.h"\n\nusing namespace v8;\n\nPersistent<Function> MyObject::constructor;\n\nMyObject::MyObject(double value) : value_(value) {\n}\n\nMyObject::~MyObject() {\n}\n\nvoid MyObject::Init() {\n  Isolate* isolate = Isolate::GetCurrent();\n\n  // Prepare constructor template\n  Local<FunctionTemplate> tpl = FunctionTemplate::New(isolate, New);\n  tpl->SetClassName(String::NewFromUtf8(isolate, "MyObject"));\n  tpl->InstanceTemplate()->SetInternalFieldCount(1);\n\n  constructor.Reset(isolate, tpl->GetFunction());\n}\n\nvoid MyObject::New(const FunctionCallbackInfo<Value>& args) {\n  Isolate* isolate = Isolate::GetCurrent();\n  HandleScope scope(isolate);\n\n  if (args.IsConstructCall()) {\n    // Invoked as constructor: `new MyObject(...)`\n    double value = args[0]->IsUndefined() ? 0 : args[0]->NumberValue();\n    MyObject* obj = new MyObject(value);\n    obj->Wrap(args.This());\n    args.GetReturnValue().Set(args.This());\n  } else {\n    // Invoked as plain function `MyObject(...)`, turn into construct call.\n    const int argc = 1;\n    Local<Value> argv[argc] = { args[0] };\n    Local<Function> cons = Local<Function>::New(isolate, constructor);\n    args.GetReturnValue().Set(cons->NewInstance(argc, argv));\n  }\n}\n\nvoid MyObject::NewInstance(const FunctionCallbackInfo<Value>& args) {\n  Isolate* isolate = Isolate::GetCurrent();\n  HandleScope scope(isolate);\n\n  const unsigned argc = 1;\n  Handle<Value> argv[argc] = { args[0] };\n  Local<Function> cons = Local<Function>::New(isolate, constructor);\n  Local<Object> instance = cons->NewInstance(argc, argv);\n\n  args.GetReturnValue().Set(instance);\n}
\n

Test it with:\n\n

\n
// test.js\nvar addon = require('./build/Release/addon');\n\nvar obj1 = addon.createObject(10);\nvar obj2 = addon.createObject(20);\nvar result = addon.add(obj1, obj2);\n\nconsole.log(result); // 30
\n", "type": "module", "displayName": "Passing wrapped objects around" } ], "type": "module", "displayName": "Addon patterns" } ], "type": "module", "displayName": "Addons" } ] }