We are happy to announce the release of WebSharper 4.4.0.

You can try it by installing the project templates for .NET Core SDK by running: dotnet new -i WebSharper.Templates::4.4.0.255
or by downloading the templates for Visual Studio 2017 here.

The main highlight of this release is the new Web Workers feature.

Web Workers are a browser feature that allows running JavaScript code in parallel of the main UI thread, taking advantage of concurrency for resource-intensive computations.

Normally, the source code for a Web Worker is a separate JavaScript file that must be passed by URL to the Worker constructor:

/// index.js:

var worker = new Worker("worker.js");

// This code runs in the main thread:
worker.postMessage("Hello, worker!");

/// worker.js:

self.onmessage = e => console.log("Received message from main thread: " + e.data);

WebSharper completely automates the creation of this file, which means you can create a worker directly in code like so:

In F#:

let worker = new Worker(fun self ->
    // This code runs in the worker:
    self.Onmessage <- fun e -> Console.Log("Received message from main thread: " + string e.Data)
)

// This code runs in the main thread:
worker.PostMessage("Hello, worker!")

In C#:

var worker = new Worker(self =>
{
    // This code runs in the worker:
    self.Onmessage = e => Console.Log("Received message from main thread: " + (string)e.Data);
});
    
// This code runs in the main thread:
worker.PostMessage("Hello, worker!");

You can learn more about this feature in the documentation.

Another addition is the proxy for the JavaScript Promise type. In addition to the type definition, we added a few bells and whistles:

• Conversion functions from and to F# Async and C# Task values: Promise.AsAsync, Promise.OfAsync, Promise.AsTask and Promise.OfTask.
• A promise computation expression to easily combine promises in F#.

Here is the full change log:

Features

• #641, #970: Add support for Web Workers.
  • Add the Worker API to WebSharper.JavaScript.
  • Add a set of special constructors for Worker which takes a function as argument. The compiler automatically compiles this function into a minimal bundle script and compiles the constructor call to reference this script by URL. See the documentation for more details.
  • Add a new compiler setting scriptBaseUrl which determines the base URL under which the worker scripts are located. The full URL is <scriptBaseUrl>/<assemblyname>/<assemblyname>.<scriptname>.js, where <scriptname> is worker unless specified in the constructor call.
• #807: Merge the class WebSharper.JavaScript.JS from the assembly WebSharper.JavaScript with the module of the same name from the assembly WebSharper.Main. This mean that all uses of JSModule in C# must be replaced with JS.
• #939: Add JavaScript Promises support. This includes:
  • Add a proxy for the Promise<'T> class.
  • Add a Promise module with functions AsAysnc, OfAsync, AsTask and OfTask.
    The As* functions handle rejected promises as follows: if the rejection value is an Error, then it is used directly as the exception raised from the Async / Task. Otherwise, it is wrapped as the Reason property of a NonStandardPromiseRejectionException.
  • Add the above functions as extension methods to their respective relevant classes.
  • Add a promise computation expression.
• #975: Drop the [Serializable] requirement for classes used in JSON serialization (RPC, Sitelets, WebSharper.Json).
• #976: Allow Bundle projects to reference other Bundle projects that have an EntryPoint.
• #979: Change signature of Router.Create to parse to option.
• #980: Sitelets: add Content.FromContent(Content<obj>) to convert an F# content into a C# content.
• #981: Add Sitelet.MapContent.
  • For F#: module function Sitelet.MapContent : (Async<Content<'T>> -> Async<Content<'T>>) -> Sitelet<'T> -> Sitelet<'T>
  • For C#: extension method Sitelet<obj> Sitelet<obj>.MapContent(Func<Task<Content>, Task<Content>>)
• #982: Make all exceptions inherit from the JavaScript Error type. This affects exceptions declared with the F# keyword exception as well as classes inheriting from System.Exception. This makes it possible to perform runtime type tests (F# :?, C# is) against System.Exception.

Fixes

• #971: WIG: properly fail when trying to declare that a class implements a class, rather than inherits from it.
• #977: Give a better error if there is a conflict where two projects include a server-side compiled quotation from the exact same file and position.
• #978: Give a better error if a Bundle is missing a project reference.
• #983: Fix dotnet build on a C# project failing to find FSharp.Core.
• WebSharper.Testing: reference QUnit via https.
• #987: Change the assemblies WebSharper.Compiler, WebSharper.Compiler.CSharp and WebSharper.Compiler.FSharp to reference FSharp.Core 4.4.1.0 rather than 4.5.0.0. This fixes assembly loading issues in the Roslyn analyzer.
  As a consequence, we reduced the minimum dependency of the WebSharper.Compiler packages on FSharp.Core from >= 4.5.0 to >= 4.1.0.

Happy coding!