May 10, 2021 Node.js
Node .js Addons is a shared object for dynamic links. H
e provides the C/C?class library capability.
These APIs are complex, and he packages the following class libraries:
V8 JavaScript, C?class library. U
sed to interact
with JavaScript,
such as creating objects, calling functions, and so on.
In
v8.h
header file (directory
deps/v8/include/v8.h
the online
address is online.
libuv, C event loop library. W ait for the file descriptor to become readable, wait for the timer, wait for the signal, and deal with libv. Or, if you need to deal with I/O, you'll use libv.
Internal Node class library.
One of the most
node::ObjectWrap
you will often derive from it.
deps/
Node has compiled all dependencies into executables, so you don't have to be mind about linking these class libraries.
All of the following examples can be downloaded at download, and perhaps you can find one from it as your extension.
Now let's write a small example of a plug-in that works in the same way as the following JS code:
module.exports.hello = function() { return 'world'; };
Create a file with
hello.cc
code:
// hello.cc
#include <node.h>
using namespace v8;
void Method(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = Isolate::GetCurrent();
HandleScope scope(isolate);
args.GetReturnValue().Set(String::NewFromUtf8(isolate, "world"));
}
void init(Handle<Object> exports) {
NODE_SET_METHOD(exports, "hello", Method);
}
NODE_MODULE(addon, init)
Note: All Node plug-ins must output an initialization function:
void Initialize (Handle<Object> exports);
NODE_MODULE(module_name, Initialize)
NODE_MODULE
does not have a sign because it is not a function (see
node.h
module_name
be the same as the binary name (suffix is .node).
The source file compiles into
addon.node
binary plug-in.
To do this, we created a
binding.gyp
file that looks a lot like JSON, which contains configuration information and is
compiled with node-gyp.
{
"targets": [
{
"target_name": "addon",
"sources": [ "hello.cc" ]
}
]
}
The next step is to create a
node-gyp configure
generates these files on the platform.
Once created, you have a
Makefile
System) file or
vcxproj
(Windows System) in the
build/
T
he
node-gyp build
to compile and generate
.node
file.
These files are
build/Release/
Now you can use these binary extensions in the Node project to
hello.js
before the
require
is
hello.node
:
// hello.js
var addon = require('./build/Release/addon');
console.log(addon.hello()); // 'world'
For more information, please refer to https://github.com/arturadib/node-qt.
Here are some addon plug-in modes to help you get started coding. The v8 reference document contains various interfaces for v8, and the Embedder's Guide document contains instructions such as handles, scopes, function templates, and so on.
Before you can use these examples, you need
node-gyp
Create
binding.gyp
file:
{
"targets": [
{
"target_name": "addon",
"sources": [ "addon.cc" ]
}
]
}
Adding a file name to an array of
sources
allows you to use multiple
.cc
such as:
"sources": ["addon.cc", "myexample.cc"]
Once
binding.gyp
ready, you can configure and compile the plug-in:
$ node-gyp configure build
Explains how to read arguments from the JavaScript function and return results from the following pattern.
Only one addon.cc
addon.cc
is required:
// addon.cc
#include <node.h>
using namespace v8;
void Add(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = Isolate::GetCurrent();
HandleScope scope(isolate);
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(Handle<Object> exports) {
NODE_SET_METHOD(exports, "add", Add);
}
NODE_MODULE(addon, Init)
You can test it with the following JavaScript snippets:
// test.js
var addon = require('./build/Release/addon');
console.log( 'This should be eight:', addon.add(3,5) );
You can also pass the JavaScript function to the C-function and execute it.
In
addon.cc
:
// addon.cc
#include <node.h>
using namespace v8;
void RunCallback(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = Isolate::GetCurrent();
HandleScope scope(isolate);
Local<Function> cb = Local<Function>::Cast(args[0]);
const unsigned argc = 1;
Local<Value> argv[argc] = { String::NewFromUtf8(isolate, "hello world") };
cb->Call(isolate->GetCurrentContext()->Global(), argc, argv);
}
void Init(Handle<Object> exports, Handle<Object> module) {
NODE_SET_METHOD(module, "exports", RunCallback);
}
NODE_MODULE(addon, Init)
Note that 2 parameters in
Init()
used in this example,
module
object is the second argument.
It allows addon to completely override
exports
You can test it with the following code:
// test.js
var addon = require('./build/Release/addon');
addon(function(msg){
console.log(msg); // 'hello world'
});
In
addon.cc
you can create and return a new object with the C-function, which
msg
that was passed in by the
createObject()
function:
// addon.cc
#include <node.h>
using namespace v8;
void CreateObject(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = Isolate::GetCurrent();
HandleScope scope(isolate);
Local<Object> obj = Object::New(isolate);
obj->Set(String::NewFromUtf8(isolate, "msg"), args[0]->ToString());
args.GetReturnValue().Set(obj);
}
void Init(Handle<Object> exports, Handle<Object> module) {
NODE_SET_METHOD(module, "exports", CreateObject);
}
NODE_MODULE(addon, Init)
Using JavaScript testing:
// test.js
var addon = require('./build/Release/addon');
var obj1 = addon('hello');
var obj2 = addon('world');
console.log(obj1.msg+' '+obj2.msg); // 'hello world'
This pattern shows how to create and return a JavaScript function, which is wrapped by a C-function:
// addon.cc
#include <node.h>
using namespace v8;
void MyFunction(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = Isolate::GetCurrent();
HandleScope scope(isolate);
args.GetReturnValue().Set(String::NewFromUtf8(isolate, "hello world"));
}
void CreateFunction(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = Isolate::GetCurrent();
HandleScope scope(isolate);
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(Handle<Object> exports, Handle<Object> module) {
NODE_SET_METHOD(module, "exports", CreateFunction);
}
NODE_MODULE(addon, Init)
Test:
// test.js
var addon = require('./build/Release/addon');
var fn = addon();
console.log(fn()); // 'hello world'
The following creates a wrapper
MyObject
for the C++ object so that he can instantiate
new
JavaScript.
First prepare
addon.cc
in the module:
// addon.cc
#include <node.h>
#include "myobject.h"
using namespace v8;
void InitAll(Handle<Object> exports) {
MyObject::Init(exports);
}
NODE_MODULE(addon, InitAll)
The
myobject.h
which
node::ObjectWrap
:
// myobject.h
#ifndef MYOBJECT_H
#define MYOBJECT_H
#include <node.h>
#include <node_object_wrap.h>
class MyObject : public node::ObjectWrap {
public:
static void Init(v8::Handle<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_;
};
#endif
Various
myobject.cc
the application, exposing the plusOne method by adding prototype properties to the
plusOne
// myobject.cc
#include "myobject.h"
using namespace v8;
Persistent<Function> MyObject::constructor;
MyObject::MyObject(double value) : value_(value) {
}
MyObject::~MyObject() {
}
void MyObject::Init(Handle<Object> exports) {
Isolate* isolate = Isolate::GetCurrent();
// 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 = Isolate::GetCurrent();
HandleScope scope(isolate);
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 = Isolate::GetCurrent();
HandleScope scope(isolate);
MyObject* obj = ObjectWrap::Unwrap<MyObject>(args.Holder());
obj->value_ += 1;
args.GetReturnValue().Set(Number::New(isolate, obj->value_));
}
Test:
// test.js
var 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
The following methods are useful when you want to create local objects and
new
want to use new initialization strictly in JavaScript:
var obj = addon.createObject();
// instead of:
// var obj = new addon.Object();
Sign
addon.cc
createObject
the addon.cc:
// addon.cc
#include <node.h>
#include "myobject.h"
using namespace v8;
void CreateObject(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = Isolate::GetCurrent();
HandleScope scope(isolate);
MyObject::NewInstance(args);
}
void InitAll(Handle<Object> exports, Handle<Object> module) {
MyObject::Init();
NODE_SET_METHOD(module, "exports", CreateObject);
}
NODE_MODULE(addon, InitAll)
There is a static method,
NewInstance
that instantiates objects (it's like JavaScript's
new
myobject.h
):
// myobject.h
#ifndef MYOBJECT_H
#define MYOBJECT_H
#include <node.h>
#include <node_object_wrap.h>
class MyObject : public node::ObjectWrap {
public:
static void Init();
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_;
};
#endif
This implementation is similar
myobject.cc
// myobject.cc
#include <node.h>
#include "myobject.h"
using namespace v8;
Persistent<Function> MyObject::constructor;
MyObject::MyObject(double value) : value_(value) {
}
MyObject::~MyObject() {
}
void MyObject::Init() {
Isolate* isolate = Isolate::GetCurrent();
// 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 = Isolate::GetCurrent();
HandleScope scope(isolate);
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 = Isolate::GetCurrent();
HandleScope scope(isolate);
const unsigned argc = 1;
Handle<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 = Isolate::GetCurrent();
HandleScope scope(isolate);
MyObject* obj = ObjectWrap::Unwrap<MyObject>(args.Holder());
obj->value_ += 1;
args.GetReturnValue().Set(Number::New(isolate, obj->value_));
}
Test:
// test.js
var 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
In addition to wrapping and returning the C-object, you can use
node::ObjectWrap::Unwrap
to unpack.
In the
addon.cc
we introduced an
add()
function that gets 2
MyObject
// addon.cc
#include <node.h>
#include <node_object_wrap.h>
#include "myobject.h"
using namespace v8;
void CreateObject(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = Isolate::GetCurrent();
HandleScope scope(isolate);
MyObject::NewInstance(args);
}
void Add(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = Isolate::GetCurrent();
HandleScope scope(isolate);
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(Handle<Object> exports) {
MyObject::Init();
NODE_SET_METHOD(exports, "createObject", CreateObject);
NODE_SET_METHOD(exports, "add", Add);
}
NODE_MODULE(addon, InitAll)
Describes
myobject.h
that uses private variables after unwrecting:
// myobject.h
#ifndef MYOBJECT_H
#define MYOBJECT_H
#include <node.h>
#include <node_object_wrap.h>
class MyObject : public node::ObjectWrap {
public:
static void Init();
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_;
};
#endif
myobject.cc
of this is similar to the previous one:
// myobject.cc
#include <node.h>
#include "myobject.h"
using namespace v8;
Persistent<Function> MyObject::constructor;
MyObject::MyObject(double value) : value_(value) {
}
MyObject::~MyObject() {
}
void MyObject::Init() {
Isolate* isolate = Isolate::GetCurrent();
// 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 = Isolate::GetCurrent();
HandleScope scope(isolate);
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 = Isolate::GetCurrent();
HandleScope scope(isolate);
const unsigned argc = 1;
Handle<Value> argv[argc] = { args[0] };
Local<Function> cons = Local<Function>::New(isolate, constructor);
Local<Object> instance = cons->NewInstance(argc, argv);
args.GetReturnValue().Set(instance);
}
Test:
// test.js
var 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
If you would like to learn more about the C-related knowledge, you can refer to this site's "C-tutorial"!