NodeJS

参考文章

http://taobaofed.org/blog/2016/09/20/type-casts-between-node-and-cpp/

https://nodejs.org/dist/latest-v8.x/docs/api/addons.html

Addons的机制，允许我们在js和c++互相调用，经常会传递参数或者返回结果，这时候需要做类型转换。包括js -> v8， 和 V8-> js。

1、js -> v8方向

#include <node.h>#include <v8.h>#include <iostream>using namespace v8;using namespace std;void GetArguments(const FunctionCallbackInfo<Value>& args) {    Isolate* isolate = args.GetIsolate();    printf("Hello GetArguments\n");    if (args.Length() == 0) {        isolate->ThrowException(Exception::TypeError(                String::NewFromUtf8(isolate, "Wrong number of arguements")));        return;    }    if (!args[0]->IsNumber()) {        printf("I am not Number \n");        return;    }    Local<Number> value1 = Local<Number>::Cast(args[0]);    cout << "first argument = " << value1->NumberValue() << endl;    Local<String> value2 = Local<String>::Cast(args[1]);    String::Utf8Value utfValue(value2);    cout << "second argument = " << string(*utfValue) << endl;}void init(Local<Object> exports) {    NODE_SET_METHOD(exports, "getArgs", GetArguments);}NODE_MODULE(addon, init)

执行 node-gyp configure build，编译cc文件。

在js文件中测试，

const addon =  require('./build/Release/addon-test');console.log("This should be eight:" + JSON.stringify(addon.getArgs(12, "Hello")));day

打印为：

Hello GetArguments
first argument = 12
second argument = Hello

可以看到，js中的参数已经传递到了v8的c++代码，并转换成了V8的类型。

2. v8->js方向

#include <node.h>#include <v8.h>using namespace v8;void MyFunction(const FunctionCallbackInfo<Value>& args) {    Isolate* isolate = args.GetIsolate();    args.GetReturnValue().Set(String::NewFromUtf8(isolate, "Hello MyFunction!"));}void TestValue(const v8::FunctionCallbackInfo<Value>& args) {    Isolate* isolate = args.GetIsolate();    printf("Hello TestValue \n");    Local<Object> obj = Object::New(isolate);    // Number type    Local<Number> number = Number::New(isolate, 100);    obj->Set(String::NewFromUtf8(isolate, "numValue"), number);    // String type    Local<String> str = String::NewFromUtf8(isolate, "Hello world!");    obj->Set(String::NewFromUtf8(isolate, "strValue"), str);    // Boolean type    Local<Boolean> flag = Boolean::New(isolate, true);    obj->Set(String::NewFromUtf8(isolate, "boolValue"), flag);    // Array type    Local<Array> array = Array::New(isolate);    array->Set(0, Number::New(isolate, 0));    array->Set(1, Number::New(isolate, 1));    array->Set(2, Number::New(isolate, 2));    array->Set(3, Number::New(isolate, 3));    obj->Set(String::NewFromUtf8(isolate, "arrayValue"), array);    // undefined type    // Local<Value> und = Undefined(isolate);    // obj->Set(String::NewFromUtf8(isolate, "undefinedValue"), und);    // Null type    // Local<Value> null = Null(isolate);    // obj->Set(String::NewFromUtf8(isolate, "nullValue"), null);    // Function type    // Local<FunctionTemplate> ft = FunctionTemplate::New(isolate, MyFunction);    // Local<Function> fn = ft->GetFunction();    // fn->SetName(String::NewFromUtf8(isolate, "myFunction"));    args.GetReturnValue().Set(obj);}void init(Local<Object> exports) {    NODE_SET_METHOD(exports, "getTestValue", TestValue);}NODE_MODULE(add, init);

js测试代码：

const addon =  require('./build/Release/addon-test');console.log("This should be eight:" + JSON.stringify(addon.getTestValue()));

生成结果为：

Hello TestValue
This should be eight:{"numValue":100,"strValue":"Hello world!","boolValue":true,"arrayValue":[0,1,2,3]}

可以看出，c++中的数据也传到了js层，并对应着不同的类型。