Elmish React Native update / view sync problem when init has Cmd

[playfulThinking]

Description

I have an React Native app (using Expo) that queues up a Cmd in the init function passed to Program.mkProgram. The Cmd does get executed in update before the first view call, but, weirdly, view gets the previous state.

Repro code

I made a minimal repro, following the counter example, modified to include a Cmd at startup:

let init () = 0, Cmd.ofMsg Increment

let update (msg:Msg) count =
    console.log "IN UPDATE"
    match msg with
    | Increment -> count + 1, Cmd.none
    | Decrement -> count - 1, Cmd.none

let Render model dispatch =
    console.log $"IN RENDER, state = {model}"
    JSX.jsx $"""
        import {{View, Text, Button}} from 'react-native'        
        <View>
            <Text>{model}</Text>
            <Button title="Increment" onPress={fun _ -> dispatch Increment} />
            <Button title="Decrement" onPress={fun _ -> dispatch Decrement} />
        </View>
    """ |> toReact 

 Program.mkProgram init update Render
        |> Program.withConsoleTrace
        |> Program.withReactNative "main"
        |> Program.run

Expected and actual results

I expected Render to show a '1'; instead, it shows '0'.

Here's the trace:

 LOG  Initial state: 0
 LOG  Updated subs: []
 LOG  New message: "Increment"
 LOG  IN UPDATE
 LOG  Updated state: 1
 LOG  Updated subs: []
 LOG  IN RENDER, state = 0

This code works when run on the web (using React Native Web) with

 Program.mkProgram init update Render
        |> Program.withConsoleTrace 
        |> Program.withReactBatched "root"
        |> Program.run

Related information

• elmish version: 4.1.0
• fable-compiler version: 4.11.0
• fable-core version:4.3.0
• Operating system: Mac Sonoma 14.2.1

Thanks much!

[et1975]

Thanks for the report. It's been a long time since I had React Native tooling setup and we didn't have Expo integration back then, so I don't have a good feel for what to look at. I'd start by looking at the generated sources to see how it aligns with Expo's samples, maybe some clue will show up.

[playfulThinking]

Thanks very much for your quick response. I appreciate any response, esp. since I'm sure practically no one is using Elmish in React Native!

I'll let you know if I figure something out. In the meantime I can work around the problem.

Best.