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A toy js -> c++ compiler written in coffeescript. Uses escodegen to write c++ and tern to figure out types.

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What's this?

It's the product of the crazy idea of using the very excellent tern.js project to figure out the types of things and use them!

js2cpp doesn't have a garbage collector yet. But it is usable and can run some JavaScript code as is!

How can I use it?

Yeah, it actually does some things. This is how js2cpp handles strings:

$ echo '"lol" + "lel"' | bin/js2cpp
#include "js2c.h"
#include <string>

String("lol") + String("lel");

And here's console.log!

$ echo 'console.log(1, 2, "3")' | bin/js2cpp
#include "js2c.h"
#include <string>

console.log(1, 2, String("3"));

It works because there's a "console" instance of a "Console" class with a variadic "log" function.

Here is tern.js figuring out a couple of types.

$ echo 'var aNumber = 1; var aString = "1";' | bin/js2cpp
#include "js2c.h"
#include <string>

double aNumber = 1;
String aString = String("1");

How do I run this? (Usage)

 ~ ♥  bin/js2cpp -h
Usage: js2cpp --run (run javascript from stdin)
Usage: js2cpp --run filename.js
Usage: js2cpp (compile from stdin)
Usage: js2cpp filename.js (compile)

environment variables:
 ~ $ RUN_VALGRIND=1 js2cpp --run ...    - Run the compiled program with `valgrind`
 ~ $ GPP_BINARY=/path/to/g++ js2cpp ... - Select what g++ binary to use (defaults to `g++`)
  • First, you need to update your compiler to a version that supports C++14. Your system probably already has this. If not, install linuxbrew or homebrew and just run brew install gcc
  • Then, clone this repo and run npm install
  • Optionally npm test just to make sure it works on your machine ;) If it doesn't please make an issue about it and I'll try to look into it. It tries to use the g++ binary from your PATH. If you want to use another binary specify it with the GPP_BINARY environment variable, like so: GPP_BINARY=g++-5 npm test.
  • To compile some javascript, run ./bin/js2cpp < your-javascript.js > your-cee-plus-plus.cpp.
  • To run it, run ./bin/js2cpp --run your-javascript.js, or ./bin/js2cpp --run, type in javascript, then press ^D when you're done. The GPP_BINARY variable also applies here.


js2cpp is kind of a frontend to fabiosantoscode/dumbjs, a javascript simplifier. It turns javascript that looks like this:

function foo(x) {
    return function () { return x }

Into something like this:

var _flatten_0 = function (_closure) {
    return _closure.x
var foo = function (x) {
    var _closure_0 = {}
    _closure_0.x = x
    return BIND(_flatten_0, _closure_0)
var main = function () {

(the BIND function must be defined elsewhere, in this case in js2cpp)

Its features are closure simulation, main-ification (put stuff in a main() function), function de-nesting, and more will come.

Since all of it is a much simpler form of javascript, it takes a huge weight off the shoulders of js2cpp and makes sure its code remains (somewhat) understandable by not mixing up concerns.

This also means that you can use dumbjs to transpile javascript to other languages. Most of its features are switchable, because not every transpilation target language will need you to do things like wrapping things in a main() function or simulating closures.



The main objective of this project is to implement at least 80% of the parts of javascript you use every day.

This means that, like a lot of npm modules which accidentally work in the browser when browserified, a lot of npm modules should accidentally work natively when js2cpp-ified.

All of the following features may be implemented in dumbjs, in this project, or in both at the same time, depending on whether they apply to each project.

  • Plug in the Boehm-Demers-Weiser conservative garbage collector (which works in C and C++, it seems!)
  • Rewrite this and dumbjs in pure javascript
  • Implement arguments and this
  • Import the most common modules from node core (mostly depends on the above), rewrite parts of them in C++ if necessary.
  • Implement promises
  • Implement boxed types, for those variables which can have 2 or more types
  • Implement JSON.parse() and JSON.stringify() (depends on the above)
  • Implement libuv bindings and shim, fake and steal node's IO APIs
  • Implement ES5-style classes (possibly by turning them into ES6-style classes first)
  • Implement or fake commonJS (require(), module.exports) modules.
  • Implement several javascript APIs such as Date, Symbol, and Array (which currently is simply a C++ std::vector).


Just have fun with it! WTFPL


A toy js -> c++ compiler written in coffeescript. Uses escodegen to write c++ and tern to figure out types.






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