js_ffi

[dependencies]
js_ffi = "0.0.14"

A simple FFI library for calling javascript from web assembly with Rust

#![no_std] + alloc for uber small wasm ( unfortunately async-await does't work with no_std yet and alloc_error_handler is only on nightly)
low magic
minimal
no macros
ready for web references
compatible with async-await futures
works with web assembly languages other than Rust
readable library that can be understood quickly and learned from

Hello World!

// get a function handle to console log javascript function
let log = register("console.log");
// call with 1 parameter with no object context and a string
call_1(UNDEFINED, log, TYPE_STRING, to_js_string("Hello World"));

Simple Example

use executor::Executor;
use js_ffi::*;

#[no_mangle]
pub fn main() -> () {
    Executor::spawn(async {
        let api = API {
            log_handle: register("console.log"),
            set_timeout_handle: register("window.setTimeout"),
        };
        api.console_log("hello");
        api.window_set_timeout(1000).await;
        api.console_log("world!");
    });
}

struct API {
    log_handle: JSValue,
    set_timeout_handle: JSValue,
}

impl API {
    pub fn console_log(&self, msg: &str) {
        call_1(UNDEFINED, self.log_handle, TYPE_STRING, to_js_string(msg));
    }

    pub fn window_set_timeout(&self, millis: i32) -> CallbackFuture {
        let (future, id) = CallbackFuture::new();
        call_2(
            UNDEFINED,
            self.set_timeout_handle,
            TYPE_FUNCTION,
            id,
            TYPE_NUM,
            millis as JSValue,
        );
        future
    }
}

<script src="https://cdn.jsdelivr.net/gh/richardanaya/js_ffi/js_ffi.js"></script>
<script>js_ffi.run("example.wasm");</script>

How it works

The basic premise is that you register the JavaScript functions you want to have access to from Rust to a constant number function handle. Then you can use call_* to send execute the function with arguments depending on the argument count you want to send (e.g. call_1, call_7). The idea is you can quickly create wrapper functions for exactly what you need. When calling the function you specify the object to call the function of (or undefined if you just want to call the function), the function id to call you registered with, and pairs of argument type and arguments afer.

call_*(<object handle>,<function id>,<arg type>,<arg>,<arg type>,<arg>,...)

Advanced

Wrap third party. Anything with its functions in global space should be able to be wrapped and invoked.

use js_ffi::*;

#[no_mangle]
fn main() {
    // register functions of things in global scope
    let jquery_handle = register("$");
    // someimes functions are hidden on prototypes of things in global scope
    let jquery_on_handle = register("jQuery.prototype.on");
    // reference your own functions created in global scope
    let alert = register("(msg)=>window.alert(msg)");

    let obj = call_1(UNDEFINED, jquery_handle, TYPE_STRING, to_js_string("body"));
    call_2(
        obj,
        jquery_on_handle,
        TYPE_STRING,
        to_js_string("click"),
        TYPE_FUNCTION,
        create_callback1(Box::new(move |_| {
            call_1(
                UNDEFINED,
                alert,
                TYPE_STRING,
                to_js_string("I was clicked!"),
            );
        })),
    );
}

<script src="https://code.jquery.com/jquery-3.4.1.min.js"></script>
<script src="https://cdn.jsdelivr.net/gh/richardanaya/js_ffi/js_ffi.js"></script>
<script>
    function say_loud(msg){
        window.alert(msg);
    }
</script>
<script>js_ffi.run("example.wasm");</script>

Don't like Rust?

The script js_ffi.js has nothing Rust specific. Everything is only done through a very basic interface

jsffiregister(i32)->i32
jsffirelease(i32)
jsfficall0(f32,i32)->f32
jsfficall1(f32,i32,i32,f32)->f32
jsfficall2(f32,i32,i32,f32,i32,f32)->f32
...
jsfficall10(f32,i32,i32,f32,i32,f32,i32,f32,i32,f32,i32,f32,i32,f32,i32,f32,i32,f32,i32,f32,i32,f32)->f32

an entry point function:

main()

and expects on your module:

jsffimalloc(i32) -> i32
jsfficallback(i32,f32,f32,f32,f32,f32,f32,f32,f32,f32,f32)

As long as your module adheres to this you can use js_ffi. Strings are simply c-strings in memorythat end in a 0 character.

License

This project is licensed under either of

Apache License, Version 2.0, (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in js_ffi by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.

js_ffi 0.0.14