Wrapping C++ code

V8 library uses v8::ObjectTemplate to bind C++ objects into JavaScript and v8::FunctionTemplate to call C++ functions from JavaScript.

Wrapping C++ functions

To create a new v8::FunctionTemplate for an arbitrary C++ function func use a function template v8::Local<v8::FunctionTemplate> v8pp::wrap_function_template(v8::Isolate* isolate, F func)

When a function generated from such a function template is being invoked in JavaScript, all function arguments will be converted from v8::Values to corresponding C++ values. Then the C++ function func will be called and its return type would be converted back to v8::Value. For the C++ function that returns void a v8::Undefined will be returned.

If the wrapped C++ function throws an exception, a v8::Exception::Error will be returned into calling JavaScript code.

A function v8::Local<v8::Function> v8pp::wrap_function(v8::Isolate* isolate, char const* name, F func) is used to wrap a C++ function to a v8::Function value. The V8 function will be created as anonymous when nullptr or "" string literal is supplied for its name:

// C++ code
int f(int x) { return x * 2; }

v8::Isolate* isolate = v8::Isolate::GetCurrent();

v8::Local<v8::Function> v8_fun = v8pp::wrap_function(isolate, "f", &f);
isolate->GetCurrentContext()-> Global()->Set(v8pp::to_v8(isolate, "v8_fun"), v8_fun);
// JavaScript code
var r = v8_fun(2); // 4

Wrapping C++ objects


Class v8pp::module in a v8pp/module.hpp header file is a thin wrapper that constructs a v8::ObjectTemplate. This class also has a constructor to re-use an existing v8::ObjectTemplate instance.

The v8pp::module class contains a number of set(name, value) function overloads that allows binding to V8 for other v8pp::modules, C++ functions, global variables, and classes wrapped with v8pp::class_ template.

These set functions return reference to the v8pp::module instance to allow call chaining:

// C++ code
v8::Isolate* isolate = v8::Isolate::GetCurrent();

int x = 1;
float fun(float a, float b) { return a + b; }

v8pp::module module(isolate), submodule(isolate);

	.set("x", x)       // bind C++ variable x
	.set("f", &fun)    // bind C++ function

	.set("sub", submodule) // bind submodule
	.set_const("PI", 3.1415926)  // bind constant

// create a  module object and bind it to the global V8 object
isolate->GetCurrentContext()-> Global()->Set(v8pp::to_v8(isolate, "module"), module.new_instance());
// JavaScript after bindings above

module.sub.x += 2; // x becomes 3 in C++
var z = module.sub(module.sub.x, module.PI); // call C++ function fun(3, 3.1415926)


A class template in v8pp/class.hpp is used to register a wrapped C++ class in v8pp and to bind the class members into V8.

Function v8pp::property() declared in a file v8pp/property.hpp allows to bind a read-only or read-write property to v8pp::class_:

struct X
	bool b;
	int c;
	X(bool b) : b(b), c(0) {}

struct Y : X
	X(int v, bool u) : X(u), var(v) {}
	int var;
	int fun() const { return var * 2;}
	int get() const { return var; }
	void set(int x) { var = x; } 

static void ext_fun(v8::FunctionCallbackInfo<v8::Value> const& args)
	Y* self = v8pp::class_<Y>::unwrap_object(args.GetIsolate(), args.This());
	if (self) args.GetReturnValue().Set(self->b);
	else args.GetReturnValue().Set(args[0]);

// bind class X
v8pp::class_<X> X_class(isolate);
	// specify X constructor signature
	// bind class member variable
	.set("b", &X::b)
	// set const property
	.set_const("str", "abc")
	// set static property
	.set_static("A", 1)
	// set static const property
	.set_static("B", 42, true)

// Bind class Y
v8pp::class_<Y> Y_class(isolate);
	// specify Y constructor signature
	.ctor<int, bool>()
	// inherit bindings from base class
	// bind member functions
	.set("get", &Y::get)
	.set("set", &Y::set)
	// bind read-only property
	.set("prop", v8pp::property(&Y::fun));
	// bind read-write property
	.set("wprop", v8pp::property(&Y::get, &Y::set));
	// bind a static function
	.set("ext_fun", &ext_fun)

// Extend existing X bindings
v8pp::class_<X>::extend(isolate).set("c", &X::c);

// set class into the module template
module.set("X", X_class);
module.set("Y", Y_class);
// Use bindings in JavaScript 
var x = new module.X(true);
assert(x.b == true);
assert(x.str == "abc");
// static property
assert(x.A === undefined);
assert(module.X.A === 1);
module.X.A = 2;
assert(module.X.A === 2);
// static const property
assert(x.B === undefined);
assert(module.X.B === 42);
module.X.B = 123;
assert(module.X.B === 42);

var y = new module.Y(10, false);
assert(y.b == false);
assert(y.get() == 10);
assert(y.prop == 20);
assert(y.get() == 11);
assert(y.wprop == 11);
y.wprop == 12;
assert(y.get() == 12);
assert(y.ext_fun() == y.b);
assert(module.Y.ext_fun(100) == 100);


Creation of wrapped classes instances can be customized by v8pp::factory<T> class template specialization. This approach allows to wrap classes with different construction policies:

class Z
	static Z* make(int) { return new Z }
	static void done(Z* z) { delete z; }
	Z() {}
	~Z() {}

// Specialize Z factory
struct v8pp::factory<Z>
	static Z* create(v8::Isolate*, int arg)
		return Z::make(arg);

	static void destroy(v8::Isolate*, Z* obj)