futurify - Js.Promise interop

[scull7]

Here is the function that I'm using for Js.Promise conversion:

  let futurify = (promise, exn) =>
    Future.make((callback) =>
      promise
      |> Js.Promise.then_(res =>
        Ok(res)
        |> callback
        |> ignore
        |> Js.Promise.resolve
      )
      |> Js.Promise.catch(error=>
        Js.String.make(error)
        |> exn
        |> (err => Error(err))
        |> callback
        |> ignore
        |> Js.Promise.resolve
      )
    );

Perhaps this may be useful?

[gilbert]

Yes, this is a great reference, thank you.

Do you have any ideas on how to differentiate between different errors? For example, imagine a postgres query potentially throwing a NoSuchColumn error or a NotUnique error. In normal JS one could write if err instanceof NotUnique). I'm wondering if that's possible to translate to reason (I haven't given much thought to it yet).

[scull7]

The exn function parameter pushes this responsibility to the caller. They are free to implement whatever scheme they like

[gilbert]

That's true, and is probably the best way to do it 👍

[scull7]

Shall I make a PR?

[gilbert]

Yes please :) Put it in a new file FutureJs.re and name it fromPromise. I'd like to keep JS-specific code in its own module, if that makes sense.

[scull7]

I've added the FutureJs.fromPromise method and associated tests.