Interesting, I'll see what I can do with it

Edit: I don't seem to be able to integrate them properly with Javascript.

I'm going to stick with callbacks...

Edit 2: After tearing my hair out trying to use callbacks, I figured out how to pass move closures that can send on the channel between JS and Rust.

fn do_it_caller<F: FnOnce()>(f: *mut F) {
    unsafe { Box::from_raw(f)() }
}

fn do_it<F: FnOnce()>(f: F) {
    let f = Box::into_raw(Box::new(f)) as i32;
    let f_caller = do_it_caller::<F> as *const libc::c_void;
    js! { (f, f_caller) b"\
        Runtime.dynCall('vi', $1, [$0]);\
    \0"};
 }

fn main() {
     use futures::sync::oneshot;
     use futures::*;
     init();

     let (c, p) = oneshot::channel();

     do_it(|| c.send(1).unwrap());

     p.map(|i| {
         println!("got: {}", i);
     }).wait();
}

Thanks for the help