WebSharper 4.1.1 is now available on NuGet, and as a vsix installer on the WebSharper website.

It contains enhancements and fixes to some client-server functionality introduced in WebSharper 4.1 (on.* server-side event handlers pre-compiling any form of quotation), special treatment of IsClient value for conditional compilation for server/client, and other bug fixes.

Documentation: WebSharper 4.1 for C# and WebSharper 4.1 for F#.

The release notes are also found on GitHub.

New features

• Server-side event handlers (on.*) and ClientSide can take any fixed F# quotation now and translates it to JavaScript.

div [] [ text "div created on the server" ]
client 
    <@ JavaScript.Console.Log "running client-side code"
       div [] [ text "div created on the client" ]
    @>

• The IsClient value (WebSharper.Pervasives.IsClient from C#) and their negations (not IsClient and !Pervasives.IsClient) can be used as a condition in branching logic in shared client-server code to make the JavaScript compiler skip the false branch entirely.

    // using WebSharper;
    if (Pervasives.IsClient) { ClientSideMethod(); } else { ServerSideMethod(); }
    var res = Pervasives.IsClient ? ClientSideMethod() : ServerSideMethod();

    if IsClient then ClientSideMethod() else ServerSideMethod()

New features in WebSharper.UI

• Added Lens function to lens into a Var using the .V syntax. Example usage:

Lens(myvar.V.MyField)
// is equivalent to:
myVar.LensAuto(fun x -> x.MyField)

This returns creates a `Var<T>` where `T` is the type of `MyField` record field, which gets and sets its value by updating the underlying `myVar`.

• Add Var<list<T>>.MapLens and .DocLens, similar in functionality to their ListModel counterpart, although with linear-time complexity. Example:

type Person = { Id: int; Name: string; Age: int }

let people =
    Var.Create (fun p -> p.Id) [
        { Id = 0; Name = "Ann"; Age = 34 }
        { Id = 1; Name = "Brian"; Age = 28 }
        { Id = 2; Name = "Clara"; Age = 43 }
    ]

let editPeople =
    people.DocLens(fun k vp ->
        form [] [
            Doc.Input [] (Lens vp.V.Name)
            Doc.IntInputUnchecked [] (Lens vp.V.Age)
        ]
    )

This ties the inputs to the values in people.Value (of type list<Person>), recreating the immutable list if any of the inputs are changed.

Fixes and improvements

• An empty F# Map passed to an RPC function is deserialized correctly.
• The behavior of the Stub attribute on constructors and static methods are now consistent with the documented translation logic since WebSharper 3.0.
• Multiple server-side event handlers and ClientSide having captured arguments within the same method do not interfere with each other.
• The client helper in WebSharper.UI is now available again within client-side code. So a div [] [ client <@ div [] [] @> ] in server side-code will create the internal div on the client (the server returning a placeholder) while fully running on the it just creates the internal div basically as if client <@ @> wrapper was not there.
• Server-side event handlers and ClientSide do not create extra functions in translated JavaScript code if their expression is containing a single static method call. These functions in back-compatibility package WebSharper.UI.Next work the same as in WebSharper 4.0.
• Some quotation forms were missing when exploring for captured arguments inside server-side on.* event handlers, including tuple gets (used by F# implicitly when passing captured a tuple value to a client-side function taking a tuple, resulting in a runtime failure). This is now working correctly:

let t = 1, 2
div [] [
    button [ on.click (fun _ _ -> Client.TestTuple t) ] [ text "click me" ] 
]