How Do I Share Code Types Between the Client and the Server?

SAFE Stack makes it really simple and easy to share code between the client and the server, since both of them are written in F#. The client side is transpiled into JavaScript by Fable, whilst the server side is compiled down to .NET CIL. Serialization between both happens in the background, so you don't have to worry about it.

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Types

Let's say the you have the following type in src/Server/Server.fs:

type Customer =
    { Id : Guid
      Name : string
      Email : string
      PhoneNumber : string }

Values and Functions

And you have the following function that is used to validate this Customer type in src/Client/Index.fs:

let customerIsValid customer =
    (Guid.Empty = customer.Id
    || String.IsNullOrEmpty customer.Name
    || String.IsNullOrEmpty customer.Email
    || String.IsNullOrEmpty customer.PhoneNumber)
    |> not

Shared

If at any point you realise you need to use both the Customer type and the customerIsValid function both in the Client and the Server, all you need to do is to move both of them to Shared project. You can either put them in the Shared.fs file, or create your own file in the Shared project (eg. Customer.fs). After this, you will be able to use both the Customer type and the customerIsValid function in both the Client and the Server.

Serialization

SAFE comes out of the box with [Fable.Remoting] or [Thoth] for serialization. These will handle transport of data seamlessly for you.

Considerations

Be careful not to place code in Shared.fs that depends on a Client or Server-specific dependency. If your code depends on Fable for example, in most cases it will not be suitable to place it in Shared, since it can only be used in Client. Similarly, if your types rely on .NET specific types in e.g. the framework class library (FCL), beware. Fable has built-in mappings for popular .NET types e.g. System.DateTime and System.Math, but you will have to write your own mappers otherwise.