What about further extending JsFuture to adapt more callback APIs?

[LittleSaya]

I found this type can be easily used on different callback APIs with just a little bit modification, maybe this could become a more general method to wrap callback APIs into Futures?

examples:

• FileSystemDirectoryEntry
• FileSystemFileEntry
• FileSystemDirectoryReader

[daxpedda]

I'm a bit lost on what you are proposing here. I would appreciate if you explain it from first principles to me.

[LittleSaya]

I think this will make using callback APIs easier (write fewer codes)

For example, for different kinds of callback APIs, we have different helper functions:

API	helper function
1 callback	fn helper1(obj: &JsValue, method: &str, args: js_sys::Array) -> Future<Output = JsValue>
2 callback	fn helper2(obj: &JsValue, method: &str, args: js_sys::Array) -> Future<Output = (JsValue, JsValue)>
3 callback	fn helper3(obj: &JsValue, method: &str, args: js_sys::Array) -> Future<Output = (JsValue, JsValue, JsValue)>

In each helper, we can retrieve method from obj and cast it into a Function, then we create an Array of Closures according to the number of callbacks and concatenate the Closure array with args, then we invoke the Function with this new concatenated array, finally cleanup Closures and fulfill the Future.

I think the problem would be the position of callback arguments, I am assuming that callback parameters are always the last arguments, I do not know if there is any API that puts callbacks before other arguments.

[daxpedda]

I see. However this isn't in scope for wasm-bindgen-futures. This project is only here to provide low-level bindings, anything beyond that should be done in higher-level crates.

What is in scope however is #4116, which would allow Promise::then() to also convey these types in the returned Promise.

This should address your issue as well, right?

[LittleSaya]

Emm, typing is not my primary concern, my real hope is erasing as much boilerplate codes as possible, but the Promise type you mentioned just inspired me, that, actually it is much easier to wrap those callback APIs into Promise in javascript side, and just use await_promise and use extern "C" to import wrapped APIs in rust side, this could eliminate a lot of glue codes and achieve the goal of 'write fewer codes' as well.