How to call a C++ method from javascript

Question

I have a C++ method (which role is killing some processes). She needs 2 parameters : a hostname and a port.

On the other hand, I am developing a web-application (using Nodejs and AngularJS), running on Google Chrome.
When I click on a button through the browser, I would like to be able to call the C++ function, through my app.js file.

I haven't found how to "bind" javascript with C++.

EDIT : I think this link could be very useful How can I use a C++ library from node.js?

score 3 · Answer 1 · 2014-05-29T11:28:19.973

You can use Google's V8. V8 is Google's open source JavaScript engine. V8 can run standalone, or can be embedded into any C++ application.

http://code.google.com/p/v8/

Following example from github demonstrates, binding a C++ class with Google V8. v8_wrap_class.cpp - Author is nicholas

/*
 * v8_wrap_class.cpp
 *
 *  Created on: 14/01/2013
 *      Author: nicholas
 *     License: public domain
 */


#include <v8.h>
#include <cstdio>
#include <string>
#include <stdexcept>
#include <memory>

using namespace v8;

/*
var Simple = function(v)
{
    this.value = v;
}
Simple.prototype.func = function()
{
    alert(this.value);
}

var obj = new Simple(4);
obj.func();
*/
struct Simple
{
    double value;

    Simple(double v)
     : value(v)
    {
        fprintf(stderr, "Simple::ctor\n");
    }

    void func()
    {
        fprintf(stderr, "Simple::func(%f)\n", value);
    }

    ~Simple()
    {
        fprintf(stderr, "Simple::dtor\n");
    }
};

namespace js
{

/*
 * Retrieve the c++ object pointer from the js object
 */
template <typename T>
T* unwrap(const Arguments& args)
{
    auto self = args.Holder();
    auto wrap = Local<External>::Cast(self->GetInternalField(0));
    return static_cast<T*>(wrap->Value());
}

/*
 * Construct a new c++ object and wrap it in a js object
 */
template <typename T, typename... Args>
Persistent<Object> make_object(Handle<Object> object, Args&&... args)
{
    auto x = new T(std::forward<Args>(args)...);
    auto obj = Persistent<Object>::New(object);
    obj->SetInternalField(0, External::New(x));

    obj.MakeWeak(x, [](Persistent<Value> obj, void* data)
    {
        auto x = static_cast<T*>(data);
        delete x;

        obj.Dispose();
        obj.Clear();
    });

    return obj;
}

}

void bind_Simple(Local<Object> global)
{
    // Name the class in js
    auto name = String::NewSymbol("Simple");

    auto tpl = FunctionTemplate::New([&](const Arguments& args) -> Handle<Value>
    {
        if (!args.IsConstructCall())
            return ThrowException(String::New("Cannot call constructor as function"));

        HandleScope scope;

        // Read and pass constructor arguments
        js::make_object<Simple>(args.This(), args[0]->NumberValue());

        return args.This();
    });

    tpl->SetClassName(name);
    tpl->InstanceTemplate()->SetInternalFieldCount(1);

    auto prototype = tpl->PrototypeTemplate();

    // Add object properties to the prototype
    // Methods, Properties, etc.
    prototype->Set(String::New("func"), FunctionTemplate::New([](const Arguments& args) -> Handle<Value>
    {
        auto s = js::unwrap<Simple>(args);
        s->func();
        return {};
    })->GetFunction());

    auto constructor = Persistent<Function>::New(tpl->GetFunction());
    global->Set(name, constructor);
}

int main()
{
    std::string js_source = R"(
        for(var i = 0; i < 1000; ++i)
        {
            var s = new Simple(4);
            s.value = 5;
            s.func();
        }
    )";

    /*
     * This code is mostly uninteresting.
     * Just run the vm with the script provided.
     */
    {
        HandleScope handle_scope;
        Handle<ObjectTemplate> global_template = ObjectTemplate::New();

        Persistent<Context> context = Context::New(0, global_template);
        Context::Scope context_scope(context);

        auto global = context->Global();

        // Wrap the class and bind to the global scope.
        bind_Simple(global);

        {
            HandleScope handle_scope;

            TryCatch trycatch;

            Local<String> source = String::New(js_source.c_str(), js_source.size());

            Local<Script> script = Script::Compile(source);
            if (script.IsEmpty())
            {
                Handle<Value> exception = trycatch.Exception();
                String::AsciiValue exception_str(exception);
                throw std::runtime_error(*exception_str);
            }

            Local<Value> result = script->Run();
            if (result.IsEmpty())
            {
                Local<Value> exception = trycatch.Exception();
                String::AsciiValue exception_str(exception);
                throw std::runtime_error(*exception_str);
            }
        }

        context.Dispose();
        context.Clear();
    }

    // Run the GC until there is nothing to reclaim.
    while (!V8::IdleNotification())
        ;
    return 0;
}

How would you use it to call a C++ function from js? Can you give an example? — doctorlove, May 29 '14 at 11:07
You'd have to wrap the whole thing up as a node addon module. Alternately, compile the C++ to a small executable you run with `child_process`. — Joe, May 29 '14 at 11:36
Brainy, if you are going to mass edit posts, make sure you fix all problems in each post. Adding [.net] to [c#] questions is not helpful on its own, please stop flooding the review queue in pursuit of +2s. — OGHaza, Jun 09 '14 at 12:47

score 0 · Answer 2 · answered May 29 '14 at 11:07

0

you can make an ajax request to your server and call c++ from there at backend maybe in php. or this maybe useful https://code.google.com/p/tiny-js/

answered May 29 '14 at 11:07

chandan kharbanda

189
2
13

How to call a C++ method from javascript

2 Answers2