Friendly C++ bindings for duktape embeddable javascript engine
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vmanucharyan Merge pull request #9 from mchiasson/patch-4
fixed broken constructor during inheritance
Latest commit e487874 Apr 14, 2018

README.md

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Summary

duktape-cpp is a library to easily bind C++ classes to duktape scripts. It aims to be easy to use and safe.

It is currently work-in-progress and may lack some features, so feel free to to contribute!

Getting started

Requirements:

  • Modern C++ compiler with C++14 support

duktape-cpp is a header-only library, so all you need is to just add source files from src directory to you project and #include "duktape-cpp/DuktapeCpp.h".

Basic example

#include <memory>
#include <iostream>

#include <duktape-cpp/DuktapeCpp.h>

namespace SpaceInvaders {

class Spaceship {
public:
    explicit Spaceship(int pos) : _pos(pos) {}

    void moveLeft() { _pos -= 1; }
    void moveRight() { _pos += 1; }

    int pos() const { return _pos; }

    /**
     * You can define `inspect` method or specialize `duk::Inspect` for your class
     */
    template <class Inspector>
    static void inspect(Inspector &i) {
        i.construct(&std::make_shared<Spaceship, int>);
        i.method("moveRight", &Spaceship::moveRight);
        i.method("moveLeft", &Spaceship::moveLeft);
        i.property("pos", &Spaceship::pos);
    }

private:
    int _pos;
};

}

DUK_CPP_DEF_CLASS_NAME(SpaceInvaders::Spaceship);

int main(int argc, char **argv) {
    try {
        /**
         * Create context
         */
        duk::Context ctx;

        /**
         * Register class.
         * Make sure the following requirements are met:
         * - Either `inspect` method or `Inspect` template specialization must be defined
         * - Class name must be defined (via DUK_CPP_DEF_CLASS_NAME macro)
         */
        ctx.registerClass<SpaceInvaders::Spaceship>();

        /**
         * Create spaceship in js
         */
        ctx.evalStringNoRes("var spaceship = new SpaceInvaders.Spaceship(5)");

        /**
         * Get pointer to spaceship
         */
        std::shared_ptr<SpaceInvaders::Spaceship> spaceship;
        ctx.getGlobal("spaceship", spaceship);
        assert(spaceship);
        assert(spaceship->pos() == 5);

        ctx.evalStringNoRes("spaceship.moveRight()");
        assert(spaceship->pos() == 6);

        spaceship->moveLeft();

        /**
         * Evaluate script and get result
         */
        int spaceshipPos = -1;
        ctx.evalString(spaceshipPos, "spaceship.pos");
        assert(spaceshipPos == 5);
    }
    catch(duk::ScriptEvaluationExcepton &e) {
        std::cout << e.what() << std::endl;
    }
}

Usage

Creating duktape context

First of all, we need to create an instance of duk::Context.

duk::Context ctx;

It is basically a wrapper around duk_context.

Defining inspectors

First, we need to tell duktape-cpp which members of class need to be exposed. This can be done by defining inspect method inside of our class.

namespace SpaceInvaders {

class Spaceship {
public:
    explicit Spaceship(int pos) : _pos(pos) {}

    void moveLeft() { _pos -= 1; }
    void moveRight() { _pos += 1; }

    int pos() const { return _pos; }
    
    template <class Inspector>
    static void inspect(Inspector &i) {
        i.method("moveRight", &Spaceship::moveRight);
        i.method("moveLeft", &Spaceship::moveLeft);
        i.property("pos", &Spaceship::pos);
    }

private:
    int _pos;
};

}

Another way of doing this, is by specializing Inspector template (for example if we want to expose class from 3rd party library):

namespace duk {

template<>
struct Inspect<SpaceInvaders::Spaceship> {
    template <class Inspector>
    static void inspect(Inspector &i) {
        i.method("moveRight", &Spaceship::moveRight);
        i.method("moveLeft", &Spaceship::moveLeft);
        i.property("pos", &Spaceship::pos);
    }
};

}

Note, that specialization must be in duk namespace

Defining class name

Then, we need to specify class name. We can do it with DUK_CPP_DEF_CLASS_NAME macro

DUK_CPP_DEF_CLASS_NAME(SpaceInvaders::Spaceship)

Full name will be translated into SpaceInvaders.Spaceship.

We can specify another (shorter) name by using DUK_CPP_DEF_SHORT_NAME macro

DUK_CPP_DEF_SHORT_NAME(SpaceInvaders::Spaceship, "Spaceship")

Constructors

If we want to be able to create a spaceship from javascript code, we have to define a constructor like this:

template <class Inspector>
static void inspect(Inspector &i) {
    i.construct(&std::make_shared<SpaceInvaders::Spaceship, int>);
}

As a constructor, we specify a function that returns shared pointer to our class. In this example, we simply use std::make_shared function, but generally we can use any function that returns shared pointer to our class.

Registering class

After we defined inspect method and class name, we can register class in duktape context;

ctx.registerClass<SpaceInvaders::Spaceship>();

Evaluating script

There are two wrapper methods in duk::Context to evaluate script - evaluateScript and evaluateScriptNoRes.

std::shared_ptr<Spaceship> res;
ctx.evalString(res, "new SpaceInvaders.Spaceship(5)");
ctx.evalStringNoRes("var spaceship = new SpaceInvaders.Spaceship(5)");

Pass objects to script

To pass object to duktape context use duk::Context::addGlobal method.

duk::Context ctx;

auto spaceship = std::make_shared<Spaceship>();
ctx.addGlobal("spaceship", spaceship);

Now we can access spaceship's methods and properties from script.

ctx.evalStringNoRes("spaceship.moveRight()");
assert(spaceship->pos() == 6);

Custom value types

Built-in value types:

  • int, double, float, bool
  • std::string
  • std::shared_ptr
  • std::unique_ptr
  • std::vector
  • std::tuple

You can define your own data type by specializing duk::Type template. Here is an example:

struct Vec3 {
    Vec3() = default;
    Vec3(float x, float y, float z) : x(x), y(y), z(z) {}

    float x {0.0f};
    float y {0.0f};
    float z {0.0f};
};

namespace duk {

template <>
struct Type<Vec3> {
    static void push(duk::Context &d, Vec3 const &val) {
        duk_push_object(d);

        duk_push_number(d, val.x);
        duk_put_prop_string(d, -2, "x");

        duk_push_number(d, val.y);
        duk_put_prop_string(d, -2, "y");

        duk_push_number(d, val.z);
        duk_put_prop_string(d, -2, "z");
    }

    static void get(duk::Context &d, Vec3 &val, int index) {
        duk_get_prop_string(d, index, "x");
        float x = float(duk_get_number(d, -1));
        duk_pop(d);

        duk_get_prop_string(d, index, "y");
        float y = float(duk_get_number(d, -1));
        duk_pop(d);

        duk_get_prop_string(d, index, "z");
        float z = float(duk_get_number(d, -1));
        duk_pop(d);

        val = Vec3(x, y, z);
    }

    static constexpr bool isPrimitive() { return true; }
};

}

As you can see, it is simply a converter to/from javascript native type.

push method defines how to push value to duktape's stack

get method defines how to get value from stack (index variable defines objects position in stack)

Please, refer to duktape documentation for details about stack manipulation.

static constexpr bool isPrimitive() { return true; } indicates, that this type is primitive. Primitive types are always passed to/from duktape context by value.

Polymorphic classes

duktape-cpp supports polymorphic types, but currently with only one level of inheritance (e.g. interface and implementation).

Use DUK_CPP_DEF_BASE_CLASS(type, base) macro to define a base class.

After that, methods and properties of base class will be automatically exposed in javascript (note, that base class also need to have inspect method or specialize Inspect template).

See tests/PolymorphicTypesTests.cpp for an example.

How to build tests and examples

git clone https://github.com/vmanucharyan/duktape-cpp.git
cd duktape-cpp
mkdir build && cd build
cmake ..
make

License (MIT)

Copyright (c) 2017 Vardan Manucharyan sd003gm@gmail.com

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.