Add new webworker template project

[ilonatommy]

Worker Class Library template ( dotnet new webworker)

Summary

Adds a new .NET Web Worker project template that provides infrastructure for running .NET code in a WebWorker, keeping your WebAssembly UI responsive during heavy computations.

Background

Blazor WASM applications with heavy computing had to rely on server requests. Computing on the UI thread interfered with UI rendering and affected UX. In .NET 10 we added an article with a sample application to make offloading heavy work to a WebWorker easier. In .NET 11 we decided to add official template support. This PR adds a project template that enables running .NET code in a WebWorker.

Template Output

MyWebWorker/
├── MyWebWorker.csproj
├── WorkerClient.cs              # C# client with factory pattern
└── wwwroot/
    ├── worker-client.js         # JS WorkerClient class
    └── dotnet-web-worker.js     # Worker entry point

Usage

# 1. Create Blazor WebAssembly app
dotnet new blazorwasm -n MyApp

# 2. Create .NET Web Worker
dotnet new webworker -n MyWebWorker

# 3. Add reference
cd MyApp
dotnet add reference ../MyWebWorker/MyWebWorker.csproj

# 4. Add AllowUnsafeBlocks to app (required for [JSExport])
# <AllowUnsafeBlocks>true</AllowUnsafeBlocks>

# 5. Create worker methods in the app

// In MyApp - worker methods with [JSExport]
[SupportedOSPlatform("browser")]
public static partial class MyWorker
{
    [JSExport]
    public static string Greet(string name) => $"Hello, {name}!";

    [JSExport]
    public static string GetUsers()
    {
        var users = new List<User> { new("Alice", 30), new("Bob", 25) };
        return JsonSerializer.Serialize(users);  // Serialize before returning
    }
}

public record User(string Name, int Age);

// In component
await using var worker = await WebWorkerClient.CreateAsync(JSRuntime);

// String result
var greeting = await worker.InvokeAsync<string>("MyApp.MyWorker.Greet", ["World"]);

// Complex result (automatically deserialized)
var users = await worker.InvokeAsync<List<User>>("MyApp.MyWorker.GetUsers", []);

Methods

public sealed class WebWorkerClient(IJSObjectReference worker) : IAsyncDisposable
{
    public static async Task<WebWorkerClient> CreateAsync(IJSRuntime jsRuntime);
    public async Task<TResult> InvokeAsync<TResult>(string method, object[] args, CancellationToken cancellationToken = default);
    public async ValueTask DisposeAsync();
}

Fixes dotnet/runtime#95452

[Copilot]

Pull request overview

This PR adds a new dotnet new webworker template that enables WebWorker support for Blazor WebAssembly applications, allowing compute-intensive .NET code to run off the main UI thread for improved responsiveness. The template provides both an infrastructure-only mode (--empty) and a full mode with demo code showcasing GitHub API integration.

Changes:

• New WebWorker item template with client library, JavaScript worker infrastructure, and optional demo files
• Integration with BlazorWeb template to optionally include WorkerClient project
• Comprehensive README documentation and localization for 13 languages

Reviewed changes

Copilot reviewed 32 out of 32 changed files in this pull request and generated 9 comments.

Show a summary per file

File	Description
src/ProjectTemplates/Web.ItemTemplates/content/WebWorker/.template.config/template.json	Template configuration defining parameters, symbols, and post-actions
src/ProjectTemplates/Web.ItemTemplates/content/WebWorker/WebWorkerTemplate.WorkerClient/WorkerClient.cs	C# client for communicating with WebWorker via JSInterop
src/ProjectTemplates/Web.ItemTemplates/content/WebWorker/WebWorkerTemplate.WorkerClient/wwwroot/worker.js	JavaScript WebWorker entry point for loading .NET runtime
src/ProjectTemplates/Web.ItemTemplates/content/WebWorker/WebWorkerTemplate.WorkerClient/wwwroot/worker-client.js	JavaScript client for managing worker lifecycle and message passing
src/ProjectTemplates/Web.ItemTemplates/content/WebWorker/Worker/GitHubWorker.cs	Demo worker class showing GitHub API data processing
src/ProjectTemplates/Web.ItemTemplates/content/WebWorker/Pages/WebWorkerDemo.razor.cs	Demo Blazor page comparing WebWorker vs UI thread performance
src/ProjectTemplates/Web.ItemTemplates/content/WebWorker/Models/GitHubModels.cs	Model classes for GitHub API responses
src/ProjectTemplates/Web.ProjectTemplates/content/BlazorWeb-CSharp/.template.config/template.json	Updated to reference WorkerClient project
src/ProjectTemplates/Web.ProjectTemplates/content/BlazorWeb-CSharp/BlazorWebCSharp.1.sln	Solution file with conditional WorkerClient project inclusion
src/ProjectTemplates/Web.ItemTemplates/Microsoft.DotNet.Web.ItemTemplates.csproj	Build configuration for generating WorkerClient.csproj
eng/Build.props	Updated to exclude template content projects from build
src/ProjectTemplates/Web.ItemTemplates/.gitignore	Ignore generated .csproj files
Multiple localization files	Translated template descriptions for 13 languages

[javiercn]

Looks good. Let's get it in for now and we'll get to play with it and refine it if necessary