Fable: The best way to perform a http request periodically and update model

[vasily-kirichenko]

What is the best way to call a http server (with fetch) asynchronously and update the model? I was thinking about a recursive promise loop, but I'm not sure how to update model in it.

(I'm afraid I asked the same question before, but I forget the answer :( )

[alfonsogarciacaro]

Yes, there was a similar discussion here: https://github.com/fable-elmish/elmish/issues/113

This is better replied by Elmish experts (@et1975, @MangelMaxime, @forki) but this should be the case for commands, though I remember you had some issues to update your model this way. I suggested to have a special Elmish version that would accept an asynchronous update function but I haven't tried myself so I'm not sure how it'd work. Did you give it a shot?

[forki]

let timerCmd intervalInMs msg =
    let configure dispatch =
        promise {
            while true do
                dispatch msg
                do! Async.Sleep intervalInMs |> Async.StartAsPromise
        }

    [configure]

let init () =  myModel, timerCmd 1000 RefreshData


let update (msg:Msg) model : Model*Cmd<Msg> = 
    match msg with
    | RefreshData -> model,Cmd.ofPromise myfetchPromise NewData FetchError
    | .....

[forki]

something like that might work

[MangelMaxime]

Yes, you can use a custom command to trigger a message inside your application like propose by @forki .

However, you probably need to be able to cancel the timer. Because, if you switch to another page you want to stop it to preserve memory ressources etc.

[vasily-kirichenko]

Thanks, guy! I'm sorry I forget about than discussion :( I use explicit message reposting with sleep, works perfectly.