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https://github.com/martinmoec/fable-react-native-how-to

A short step-by-step guide to get started developing mobile apps with F# and Fable in React Native
https://github.com/martinmoec/fable-react-native-how-to

fable fable-elmish fable-react-native fsharp fsharp-app-development fsharp-react-native react-native

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A short step-by-step guide to get started developing mobile apps with F# and Fable in React Native

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# How-to: Set up React Native with F# and Fable



This is a step-by-step guide which aims to help you set up a React Native project with F# and Fable. The [Fable compiler](https://github.com/fable-compiler/Fable) generates JavaScript from your F# source code, and enables you to write React Native apps targeting iOS and Android almost completely through F#! Since the Fable compiler is just generating pure JavaScript from our F# source code we should be able to target any platform through React Native (Windows, MacOS, Web), though i have not tested this myself. Feel free to share your own experience with any of these platforms.



Sample files for getting started can be found within this repository. 



## Requirements

- React Native

- Watchman

- Node.js

- .NET Core >= 3.0

- npm



# Setup a new React Native project



This how-to will not go into detail on how to install React Native and how React Native works. When you have React Native installed you can create a new project by running `react-native init `



You should test that your basic React Native project compiles/runs before moving further.



`npx react-native run-ios` or `npx react-native run-android`



# Setup the F# project

Create a folder to hold your F# project and add a `.fsproj` file with a simple `.fs` file. In this example i will create a `src` folder in the project root directory which contains the files `App.fsproj` and `App.fs`.



## `App.fsproj`

```xml



  

    netstandard2.1

  

  

    

  

  

    

    

    

    

    

  



```



## `App.fs`

```fsharp

module App



open Elmish

open Elmish.React

open Elmish.ReactNative

open Fable.ReactNative



// A very simple app which increments a number when you press a button



type Model = {

    Counter : int

}



type Message =

    | Increment 



let init () = {Counter = 0}, Cmd.none



let update msg model =

    match msg  with

    | Increment ->

        {model with Counter = model.Counter + 1}, Cmd.none 



module R = Fable.ReactNative.Helpers

module P = Fable.ReactNative.Props

open Fable.ReactNative.Props



let view model dispatch =

    R.view [

        P.ViewProperties.Style [ 

            P.FlexStyle.Flex 1.0 

            P.FlexStyle.JustifyContent JustifyContent.Center

            P.BackgroundColor "#131313" ]

    ] [

        

        

        R.text [

            P.TextProperties.Style [ P.Color "#ffffff" ]

        ] "Press me"

        |> R.touchableHighlightWithChild [

            P.TouchableHighlightProperties.Style [

                P.FlexStyle.Padding (R.dip 10.)

            ]

            P.TouchableHighlightProperties.UnderlayColor "#f6f6f6"

            OnPress (fun _ -> dispatch Increment) 

        ]



        R.text [

            P.TextProperties.Style [

                P.Color "#ffffff"

                P.FontSize 30.

                P.TextAlign P.TextAlignment.Center

            ]

        ] (string model.Counter)

    ]



Program.mkProgram init update view

|> Program.withConsoleTrace

|> Program.withReactNative "Your project name" // CHANGE ME

|> Program.run

```



IMPORTANT: Feed the name of your project in `Program.withReactNative` (the same you used for `react-native init` )



# Install Fable tool



`dotnet new tool-manifest && dotnet tool install fable`



# Install npm-packages



Install the [@babel/preset-env](https://www.npmjs.com/package/@babel/preset-env) npm-module as a dev-dependency. See the documentation of these for further info.



`npm install --save-dev @babel/preset-env` 



You will also need to install the [buffer](https://www.npmjs.com/package/buffer) npm-module, along with the [@react-native-community/netinfo](https://www.npmjs.com/package/@react-native-community/netinfo) module which is required by Fable.React.Native.



`npm install buffer @react-native-community/netinfo`



You can now compile your F# project to Javascript by simply running `dotnet fable ./src -o ./out`

(Note the `-o` parameter specifying the output folder to dump the .js files) 



If you get a compilation error it is likely to be caused by your `babel.config.js` file, and i've experienced that the easiest way to get rid of this i simply by deleting the `babel.config.js` file altogether. You can also provide a configuration file as shown below. However, someone with a better Babel understanding than me could probably provide a better configuration/setup (suggestions welcomed).



#### Tips:

```json

"build": "dotnet fable ./src -o ./out",

"watch": "dotnet fable watch ./src -o ./out"

```

Add the above JSON to the `scripts` section of the `packages.json` file and simply call `npm run build` to compile. Run `npm run watch` in order to watch for changes and enable hot-reloading as you change your F# code.



# Importing the generated JavaScript

Now you can compile your F# code to JavaScript and dump it to a folder (`./out` used in this example).



1. Delete your default `App.js` file in the root directory.

2. Update your `index.js` file:

    ```js

    /**

    * @format

    */



    import { AppRegistry } from 'react-native';

    import * as App from './out/App';

    import { name as appName } from './app.json';

    ```

Notice that we import App from our generated files in the `out` folder. The app registration call is also removed, as this is now handled in our F# code.



# You're good to go! 

1. Compile F# to JavaScript and watch for changes

    - `dotnet fable watch ./src -o ./out`

    - or `npm run watch` if you altered the `scripts` section of `packages.json`

2. Run app

    - `npx react-native run-ios|android`

3. Watch as the app updates along with your F# code. Enjoy!



# More

- For larger apps you might want to opt out of Elmish and include navigation. Take a look at the following [how-to](navigation)