基于V8引擎的C++和JS的相互交互

基于什么原因略！

1. 脚本引擎的基本功能

V8只是一个JS引擎。去除它的特点功能出处，它必须要实现JS引擎的几个基础功能：

• 脚本执行：
  • 脚本可能是一个表达式；一段js代码；或者一个文件
  • 执行表达式返回js表达式对应的值
    
• C++来取设JS的内容
  • 获取JS内容的数据(包括基础数据类型、数组、日期等)、对象（类的一个实例）、类或函数
  • 设置JS内容的数据
    
• JS来取设C++的内容
  • C++为js动态添加类（例如：Date，可以通过new Date()来创建任意多个对象）
  • C++为js动态添加全局对象（例如：Math，可以直接调用其全局方法如Math.min）

我们的目的是先学会怎么用，再去想为什么！

2. V8 脚本引擎基本功能实现

带着这几个目的去使用V8，找遍网上资料，发现很少有覆盖周全的。其实翻来覆去就是那几个资料，理论派居多；最可气的是按照那些例子去跑，怎么都会运行错误；而且在关键的地方全按照google伪代码例子照搬。不过理论派的阐述确实很一本正经；很精辟。也感谢先行者！

2. 1 V8之脚本运行

2.1.1 获取字符串：

void test_String(){  Handle<String> source = String::New("'Hello' + ', World!'");  Handle<Script> script = Script::Compile(source);  Handle<Value> result = script->Run();  String::AsciiValue ascii(result);  printf("%s\n", *ascii);}
>>> Hello，World!

2.1.2 获取数组：

void test_Array(){  Handle<String> source = String::New("[1, 2, 'hello', 6+5]");  Handle<Script> script = Script::Compile(source);  Handle<Value> result = script->Run();  String::AsciiValue ascii(result);  printf("%s\n", *ascii);}
>>> 1,2,hello,11

2. 2 V8之C++取设JS

2.2.1 获取成员之数据

void test_getjs_data(Handle<Context> pContext){ Handle<String> source = String::New("var s1 = 8+5;"); Handle<Script> script = Script::Compile(source); Handle<Value> result = script->Run(); Handle<String> js_data = String::New("s1"); Handle<Value> js_data_value = pContext->Global()->Get(js_data); String::AsciiValue ascii(js_data_value); printf("%s\n", *ascii);}
>>> 13

2.2.2 获取成员之全局对象

void test_getjs_dataofObject(Handle<Context> pContext){ Handle<String> source = String::New("function Point(x,y){this.x=x; this.y=y;} var pt=new Point(10,20);"); Handle<Script> script = Script::Compile(source); Handle<Value> result = script->Run(); Handle<String> js_data = String::New("pt"); Handle<Value> js_data_value = pContext->Global()->Get(js_data); // Convert the result to an ASCII string and print it. {  String::AsciiValue ascii(js_data_value);  printf("pt = %s\n", *ascii); } Handle<Object> js_data_object = Handle<Object>::Cast(js_data_value); Handle<Value> key = String::New("x"); Handle<Value> objX = js_data_object->Get(key); {  String::AsciiValue ascii(objX);  printf("pt.x = %s\n", *ascii); }}
>>> pt = [object Object]    pt.x = 10

2.2.3 获取js 类

void test_getjs_dataofObjectClass(Handle<Context> pContext){ Handle<String> source = String::New("function Point(x,y){this.x=x; this.y=y;} Point.prototype.show=function(){return '(x,y) = '+this.x+','+this.y;}"); Handle<Script> script = Script::Compile(source); Handle<Value> result = script->Run(); Handle<String> js_data = String::New("Point"); Handle<Value> js_data_value = pContext->Global()->Get(js_data); // Convert the result to an ASCII string and print it. {  String::AsciiValue ascii(js_data_value);  printf("Point = %s\n", *ascii); } bool bIsFunction = js_data_value->IsFunction(); if(bIsFunction) {  printf("Point is function\n"); } bool bIsObject = js_data_value->IsObject(); if(bIsObject) {  printf("Point is object\n"); } Handle<Object> js_data_object = Handle<Object>::Cast(js_data_value); // var newObj = new Point(1,2); Handle<Value>  argv[2] ;  argv[0] = Int32::New(1); argv[1] = Int32::New(2); Handle<Value> newObj = js_data_object->CallAsConstructor(2, argv); {  bool bIsFunction = newObj->IsFunction();  if(bIsFunction) //-false-  {   printf("newObj is function\n");  }  bool bIsObject = newObj->IsObject();  if(bIsObject) //-true-  {   printf("newObj is object\n");  } } // newObj.show(); {  Handle<Object> obj = Handle<Object>::Cast(newObj);  Handle<String> js_func_name = String::New("show");  Handle<Value>  js_func_ref = obj->Get(js_func_name);  Handle<Function> js_func = Handle<Function>::Cast(js_func_ref);  js_data_value = js_func->Call(obj, 0, NULL) ;   String::AsciiValue ascii(js_data_value);  printf("newObj.show() = %s\n", *ascii); }}
>>> Point = function Point(x,y){this.x=x; this.y=y;}Point is functionPoint is objectnewObj is objectnewObj.show() = (x,y) = 1,2

2. 3 V8之JS取设C++

2.3.0 js 和 C++的关联

c++ 和 js对应。特别是为达到能在Js中使用var obj = new CObject()，参照CreateObjectToJs方法

void test_getc_loadObjectTemplate(Handle<ObjectTemplate> pObj){ //-load c++'s data- pObj->SetAccessor(String::New("x"), XGetter, XSetter);  //-load c++'s function- pObj->Set(String::New("setColor"),FunctionTemplate::New(set_color)); //-load c++'s class- CreateObjectToJs(pObj);}
Point* NewPointFunction(const Arguments & args) {  if(args.Length()==2)  {   Local<Value> v1 = args[0];   Local<Value> v2 = args[1];   return new Point( v1->Int32Value(), v2->Int32Value() );  }  else  return new Point(); }void PointWeakExternalReferenceCallback(Persistent<Value>, void* parameter){ if (Point* cpp_object = static_cast<Point*>(parameter))  delete cpp_object;}Persistent<External> NewWeakExternalPoint(void* parameter){ Persistent<External> ret = Persistent<External>::New(External::New(parameter)); ret.MakeWeak(parameter, PointWeakExternalReferenceCallback); return ret;}Handle<Value> PointFunctionInvocationCallback(const Arguments &args) { if (!args.IsConstructCall()) return Undefined(); Point* cpp_object = NewPointFunction(args); if (!cpp_object) return ThrowException(String::New("Can not create Object in C++")); args.Holder()->SetInternalField(0, NewWeakExternalPoint(cpp_object)); return Undefined(); }
void CreateObjectToJs(Handle<ObjectTemplate> pObj){  Point* p = new Point(0, 0); Handle<FunctionTemplate> point_templ = FunctionTemplate::New(&PointFunctionInvocationCallback, External::New(p)); point_templ->SetClassName(String::New("Point")); point_templ->InstanceTemplate()->SetInternalFieldCount(1); Handle<ObjectTemplate> point_proto = point_templ->PrototypeTemplate(); point_proto->SetAccessor(String::New("x"), GetPointX, SetPointX); point_proto->SetAccessor(String::New("y"), GetPointY, SetPointY); point_proto->Set(String::New("show"), FunctionTemplate::New(ShowPoint)); pObj->Set(String::New("Point"), point_templ);}

2.3.1 全局函数

c++: 

Handle<Value> set_color(const Arguments & args) {  Handle<Value>  rtn;  if(args.Length() == 3)   { int r = args[0]->Int32Value(); int g = args[1]->Int32Value(); int b = args[2]->Int32Value();   char szTmp[80] = ""; _stprintf(szTmp,"RGB%2X%02X%02X", r,g,b); rtn = String::New(szTmp);  }  else   rtn = Undefined();    return  rtn;}

js:

void test_getc_function(Handle<Context> pContext, Handle<ObjectTemplate> pObj){ Handle<String> source = String::New("var data = setColor(255,128,0);"); Handle<Script> script = Script::Compile(source);   Handle<Value> result = script->Run(); Handle<String> js_data = String::New("data"); Handle<Value> js_data_value = pContext->Global()->Get(js_data); // Convert the result to an ASCII string and print it. String::AsciiValue ascii(js_data_value); printf("%s\n", *ascii);}
>>> RGBFF8000

2.3.2 全局数据

c++:

int x = 0;Handle<Value> XGetter(Local<String> key,const AccessorInfo& info) {    return Integer::New(x);} void XSetter(Local<String> key, Local<Value> value,const AccessorInfo& info) {    x = value->Int32Value();}

js:

void test_getc_data(Handle<Context> pContext, Handle<ObjectTemplate> pObj){ Handle<String> source = String::New("var data1 = x; x=200; var data2=x;"); Handle<Script> script = Script::Compile(source); Handle<Value> result = script->Run(); {  Handle<String> js_data = String::New("data1");  Handle<Value> js_data_value = pContext->Global()->Get(js_data);  String::AsciiValue ascii(js_data_value);  printf("data1 = %s\n", *ascii);  } {  Handle<String> js_data = String::New("data2");  Handle<Value> js_data_value = pContext->Global()->Get(js_data);  String::AsciiValue ascii(js_data_value);  printf("data2 = %s\n", *ascii);  }}
>>> data1 = 0data2 = 200

2.3.3 类

c++

struct Point {    Point()  {  x_ = 0;  y_ = 0; }    Point(int x, int y)  {  x_ = x;  y_ = y; }     int getX() const {   return x_;  }    int getY() const { return y_; }    void setX(int value) { x_ = value; }    void setY(int value) { y_ = value; }    bool isNull() const { return x_ == 0 && y_ == 0; } void show() {  char szTmp[80] = "";  _stprintf(szTmp, "x,y = %d,%d\n", x_, y_);  printf(szTmp); }    int x_, y_; };
Handle<Value> GetPointX(Local<String> key,const AccessorInfo &info) {   Handle<Object> obj = info.This ();
    //Local<Object> self = info.Holder(); //使用此种方法会死!!!-    Point& point = *static_cast<Point*> (Local<External>::Cast(obj->GetInternalField(0))->Value ());  int value = point.x_;    return Integer::New(value);}void SetPointX(Local<String> key, Local<Value> value,const AccessorInfo& info) { Handle<Object> obj = info.This (); Point& point = *static_cast<Point*> (Local<External>::Cast(obj->GetInternalField(0))->Value ());  point.x_ = value->Int32Value();}Handle<Value> GetPointY(Local<String> key,const AccessorInfo &info) {    Local<Object> self = info.Holder();    Local<External> wrap = Local<External>::Cast(self->GetInternalField(0));    void* ptr = wrap->Value();    int value = static_cast<Point*>(ptr)->y_;    return Integer::New(value);}void SetPointY(Local<String> key, Local<Value> value,const AccessorInfo& info) { Local<Object> self = info.Holder(); Local<External> wrap = Local<External>::Cast(self->GetInternalField(0)); void* ptr = wrap->Value(); static_cast<Point*>(ptr)->y_ = value->Int32Value();}Handle<Value> ShowPoint(const Arguments& args){ Local<Object> self = args.Holder(); //Local<Object> self = info.Holder(); Local<External> wrap = Local<External>::Cast(self->GetInternalField(0)); void* ptr = wrap->Value(); static_cast<Point*>(ptr)->show();    return Undefined();}

js

void test_getc_object(Handle<Context> pContext, Handle<ObjectTemplate> pObj){ test_getobject(pContext);return; // Create a string containing the JavaScript source code. Handle<String> source = String::New("var pt=new Point(10,20);"); // Compile the source code. Handle<Script> script = Script::Compile(source);   // Run the script to get the result. Handle<Value> result = script->Run(); Handle<String> js_data = String::New("pt"); Handle<Value> js_data_value = pContext->Global()->Get(js_data); // Convert the result to an ASCII string and print it. {  String::AsciiValue ascii(js_data_value);  printf("pt = %s\n", *ascii); } Handle<Object> js_data_object = Handle<Object>::Cast(js_data_value); Handle<Value> key = String::New("x"); Handle<Value> objX = js_data_object->Get(key); {  String::AsciiValue ascii(objX);  printf("pt.x = %s\n", *ascii); }}
>>> Point = function Point() { [native code] }Point is functionPoint is objectnewObj is objectsrc obj.x = 3last obj.x = 30begin newObj.show() : x,y = 30,4newObj.show() = undefined

3. 教训

• 在VS200X C++中，请都使用/MDD 编译选项
• 对于类，需要绑定一个构造函数，主要目的是用来生成C++对象。该对象千万不要使用局部变量，而要是指针
• 对于C++扩展的类，通过FunctionTemplate来实现；而不要使用ObjectTemplate

• 对于JS中的全局对象，可以通过ObjectTemplate来实现。实际上就是绑定全局API和变量

http://iammr.7.blog.163.com/blog/static/49102699201201565822189/