Use of async for Get, GetJSON, etc. calls

[Dmitri Nesteruk]

I have a HTML Sitelet app that uses JQuery to consume JSONP from RESTful services. Typically my code looks like the following:

JQuery.GetJSON(url, fun x y -> process(x))

I was wondering if it was possible to somehow coerce WebSharper to use the async notation here.

What I mean is, I'd much prefer to write

async {

  let! (x, y) = JQuery.GetJSON(url)

}

Just curious if this is somehow possible or whether this sort of thing is planned.

[Vladimir Matveev]

Yes, this is possible, something like this:

 

    [<AutoOpen>]
    module JsonExtensions = 

        open IntelliFactory.WebSharper.JQuery
        type JQuery with
            [<JavaScript>]
            static member GetJsonAsync(url : string, ?data : obj) = 
                Async.FromContinuations <|
                    fun (ok, _, _) ->
                        let cont (r : obj, _ : string) = ok (r :?> _)
                        match data with
                        | Some d -> JQuery.GetJSON(url, d, cont)
                        | None -> JQuery.GetJSON(url, cont)
                        |> ignore

 

//…

        [<JavaScript>]
        override this.Body =
            Button [Text "Click"]
            |>! OnClick (fun _ _ ->
                async {
                    let! (res : string) = JQuery.JQuery.GetJsonAsync("http://api.twitter.com/1/help/test.json?callback=?" )
                    JavaScript.Alert(res)                        
                }
                |> Async.Ignore
                |> Async.StartImmediate
            ) :> _

[Dmitri Nesteruk]

Thanks! However, I'm not sure I understand how to catch errors in this one. Seems like the second parameter to 'cont' is just thrown away...

[Zakaluka]

Sorry to resurrect an old thread (I'm sure people have already found the solution), but here's what I came up with:

[<AutoOpen>]
module JQueryExt =

  open IntelliFactory.WebSharper.JQuery
  type JQuery with
    [<JavaScript>]
    static member GetJsonAsync(url : string, ?data : obj) =
      Async.FromContinuations <|
        fun (ok, _, _) ->

          let cont (retData : obj, status : string) = ok (retData, status)

          match data with
          | Some d -> JQuery.GetJSON(url, d, cont)
          | None -> JQuery.GetJSON(url, cont)
          |> ignore

...

      [<JavaScript>]
      override this.Body =
        Button [Text "what?"]
          |>! OnClick (fun elem args ->
            async {
              let! ret, status = JQuery.GetJsonAsync("http://api.twitter.com/1/help/test.json?callback=?")
              JavaScript.Alert(ret.ToString() + "\n" + status)
            }
            |> Async.Ignore
            |> Async.Start
          )
        :> IPagelet

Even though the 'ok' continuation is constrained from 'a to (obj * string), that should be okay because the success callback method for GetJSON has that argument as its input signature.

Did anyone else come up with anything similar?

Regards,

z.