SpawnDev.BlazorJS.WebWorkers v2.2.83 — nugetz

LostBeard/SpawnDev.BlazorJS.WebWorkersv2.2.83

Name: SpawnDev.BlazorJS.WebWorkers
Author: LostBeard

.NET 8.0.NET 9.0.NET 10.0

Call Services and static methods in separate threads with WebWorkers and SharedWebWorkers. Run Blazor WASM in the ServiceWorker.

github.com ↗

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Deps

Install Size

—

Vulns

✓ 0

Published

Feb 12, 2026

Get Started

$ dotnet add package SpawnDev.BlazorJS.WebWorkers

Readme

NuGet

Package	Description
SpawnDev.BlazorJS <br />	Enhanced Blazor WebAssembly Javascript interop
SpawnDev.BlazorJS.WebWorkers <br />	Blazor WASM WebWorkers, SharedWebWorkers, and ServiceWorker

Documentation
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SpawnDev.BlazorJS

Full Blazor WebAssembly and Javascript interop. Create, access properties, call methods, and add/remove event handlers of any Javascript objects the .Net way without writing Javascript.

Supported .Net Versions

// ... other usings
using SpawnDev.BlazorJS;

// ... normal builder code
var builder = WebAssemblyHostBuilder.CreateDefault(args);
builder.RootComponents.Add<App>("#app");
builder.RootComponents.Add<HeadOutlet>("head::after");
// Services section
// Add SpawnDev.BlazorJS.BlazorJSRuntime
builder.Services.AddBlazorJSRuntime();
// ... more app services (such as WebWorkerService if needed)
// build and Init using BlazorJSRunAsync (instead of RunAsync)
await builder.Build().BlazorJSRunAsync();

[Inject]
BlazorJSRuntime JS { get; set; }

// Get and Set
var innerHeight = JS.Get<int>("window.innerHeight");
JS.Set("document.title", "Hello World!");

// Call
var item = JS.Call<string?>("localStorage.getItem", "itemName");
JS.CallVoid("addEventListener", "resize", Callback.Create(() => Console.WriteLine("WindowResized"), _callBacks));

// Attach events
using var window = JS.Get<Window>("window");
window.OnOffline += Window_OnOffline;

// AddEventListener and RemoveEventListener are supported on all EventTarget objects
window.AddEventListener("resize", Window_OnResize, true);

window.RemoveEventListener("resize", Window_OnResize, true);

// Javascript
function AddNum(num1, num2){
    return num1 + num2;
}

// C#
var total = JS.Call<int>("AddNum", 20, 22);
// total == 42 here

// Javascript
async function AddNum(num1, num2){
    return num1 + num2;
}

// C#
var total = await JS.CallAsync<int>("AddNum", 20, 22);
// total == 42 here

// Javascript
function AddNum(num1, num2){
    return new Promise((resolve, reject)=>{
        resolve(num1 + num2);
    });
}

// C#
var total = await JS.CallAsync<int>("AddNum", 20, 22);
// total == 42 here

// Get Set
var window = JS.Get<IJSInProcessObjectReference>("window");
window.Set("myVar", 5);
var myVar = window.Get<int>("myVar");

// Call
window.CallVoid("addEventListener", "resize", Callback.Create(() => Console.WriteLine("WindowResized")));

IJSInProcessObjectReference worker = JS.New("Worker", myWorkerScript);

// This is how JSEventCallback is implemented in the Window class
public JSEventCallback<StorageEvent> OnStorage { get => new JSEventCallback<StorageEvent>(o => AddEventListener("storage", o), o => RemoveEventListener("storage", o)); set { /** set MUST BE HERE TO ENABLE += -= operands **/ } }

void AttachEventHandlersExample()
{
    using var window = JS.Get<Window>("window");
    // If this is the first time Window_OnStorage has been attached to an event a .Net reference is automatically created and held for future use and removal
    window.OnStorage += Window_OnStorage;
    // the window JSObject reference can safely be disposed as the .Net reference is attached to Window_OnStorage internally
}
void DetachEventHandlersExample()
{
    using var window = JS.Get<Window>("window");
    // If this is the last reference of Window_OnStorage being removed then the .Net reference will automatically be disposed.
    // IMPORTANT - detaching is important for preventing resource leaks. .Net references are only released when the reference count reaches zero (same number of -= as += used)
    window.OnStorage -= Window_OnStorage;
}

void AttachEventHandlersExample()
{
    using var window = JS.Get<Window>("window");
    window.OnStorage += Window_OnStorage;
}
void DetachEventHandlersExample()
{
    using var window = JS.Get<Window>("window");
    window.OnStorage -= Window_OnStorage;
}
// The method below is not using the optional StorageEvent argument
void Window_OnStorage()
{
    Console.WriteLine($"StorageEvent");
}

var tcs = new TaskCompletionSource<bool>();
var callback = () =>
{
    tcs.TrySetResult(true);
};
JS.CallVoid("setTimeout", callback, 100);
await tcs.Task;
callback.DisposeJS();

int testValue = 42;
var origFunc = new Func<int, int>((val) =>
{
    return val;
});
// set a global Javascript var to our Func<int>
// if this is the first time this Func is passed to Javascript a Callback will be created and associated to this Func for use in future serialization
// the auto created Callback must be disposed by calling the extension method Func.DisposeJS()
JS.Set("_funcCallback", origFunc);
// read back in our Func as an Func 
// internally a Javascript Function reference is created and associated with this Func.
// the auto created Function must be disposed by calling the extension method Func.DisposeJS()
var readFunc = JS.Get<Func<int, int>>("_funcCallback");
var readVal = readFunc(testValue);
if (readVal != testValue) throw new Exception("Unexpected result");
// dispose the Function created and associated with the read Func
readFunc.DisposeJS();
// dispose the Callback created and associated with the original Func
origFunc.DisposeJS();

JS.Set("testCallback", Callback.Create<string>((strArg) => {
    Console.WriteLine($"Javascript sent: {strArg}");
    // this prints "Hello callback!"
}));

// in Javascript
testCallback('Hello callback!');

string SomeNetFn(string input){
    return $"Recvd: {input}";
}

JS.Set("someNetFn", Callback.CreateOne<string, string>(SomeNetFn));

// in Javascript
someNetFn('Hello callback!');

// prints
Recvd: Hello callback!

async Task<string> SomeNetFnAsync(string input){
    return $"Recvd: {input}";
}

JS.Set("someNetFnAsync", Callback.CreateOne<string, string>(SomeNetFnAsync));

// in Javascript
await someNetFnAsync('Hello callback!');

// prints
Recvd: Hello callback!

// create an interface for your Javascript object that implements IJSObject
public interface IWindow : IJSObject 
{
    string Name { get; set; }
    void Alert(string msg = "");
    // ...
}

// use your IJSObject interface to interact with the Javascript object
public void IJSObjectInterfaceTest() {
    var w = JS.Get<IWindow>("window");
    var randName = Guid.NewGuid().ToString();
    // directly set the window.name property
    w.Name = randName;
    // verify the read back
    if (w.Name != randName) throw new Exception("Interface property set/get failed");
}

// create a class for your Javascript object that inherits from JSObject
public class Window : JSObject 
{
    // required constructor
    public Window(IJSInProcessObjectReference _ref) : base(_ref) { }
    public string Name { get => JSRef.Get<string>("name"); set => JSRef.Set("name", value); }
    public void Alert(string msg = "") => JSRef.CallVoid(msg);
    // ...
}

// use the JSObject class to interact with the Javascript object
public void JSObjectClassTest() {
    var w = JS.Get<Window>("window");
    var randName = Guid.NewGuid().ToString();
    // directly set the window.name property
    w.Name = randName;
    // verify the read back
    if (w.Name != randName) throw new Exception("Interface property set/get failed");
}

public class Window : EventTarget {
    // all JSObject types must have this constructor
    public Window(IJSInProcessObjectReference _ref) : base(_ref) { }
    // here is a property with both getter and setter
    public string? Name { get => JSRef.Get<string>("name"); set => JSRef.Set("name", value); }
    // here is a read only property that returns another JSObject type
    public Storage LocalStorage => JSRef.Get<Storage>("localStorage");
    // here are methods
    public long SetTimeout(Callback callback, double delay) => JSRef.Call<long>("setTimeout", callback, delay);
    public void ClearTimeout(long requestId) => JSRef.CallVoid("clearTimeout", requestId);    
    // ... 
}

// below the JSObject derived Window class is used
using var window = JS.Get<Window>("window");
var randName = Guid.NewGuid().ToString();
// set and get properties
window.Name = randName;
var name = window.Name;
// call methods
window.Alert("Hello!");

var promise = new Promise();
// pass to Javascript api
...
// then later resolve
promise.Resolve();

var promise = new Promise(async () => {
    await Task.Delay(5000);
});
// pass to Javascript api

var promise = new Promise<string>(async () => {
    await Task.Delay(5000);
    return "Hello world!";
});
// pass to Javascript api

var taskSource = new TaskCompletionSource<string>();
var promise = new Promise<string>(taskSource.Task);
// pass to Javascript api
...
// then later resolve
taskSource.TrySetResult("Hello world!");

using var navigator = JS.Get<Navigator>("navigator");
using var locks = navigator.Locks;

Console.WriteLine($"lock: 1");

using var waitLock = locks.Request("my_lock", Callback.CreateOne((Lock lockObj) => new Promise(async () => {
    Console.WriteLine($"lock acquired 3");
    await Task.Delay(5000);
    Console.WriteLine($"lock released 4");
})));

using var waitLock2 = locks.Request("my_lock", Callback.CreateOne((Lock lockObj) => new Promise(async () => {
    Console.WriteLine($"lock acquired 5");
    await Task.Delay(5000);
    Console.WriteLine($"lock released 6");
})));

Console.WriteLine($"lock: 2");

var audio = JS.New("Audio", "https://some_audio_online");
audio.CallVoid("play");

public class Audio : JSObject
{
    public Audio(IJSInProcessObjectReference _ref) : base(_ref) { }
    public Audio(string url) : base(JS.New("Audio", url)) { }
    public void Play() => JSRef.CallVoid("play");
}

var audio = new Audio("https://some_audio_online");
audio.Play();

void UnionTypeTestMethod(string varName, Union<bool?, string?>? unionTypeValue)
{
    JS.Set(varName, unionTypeValue);
}

var stringValue = "Hello world!";
UnionTypeTestMethod("_stringUnionValue", stringValue);
if (stringValue != JS.Get<string?>("_stringUnionValue")) throw new Exception("Unexpected result");

var boolValue = true;
UnionTypeTestMethod("_boolUnionValue", boolValue);
if (boolValue != JS.Get<bool?>("_boolUnionValue")) throw new Exception("Unexpected result");

// an example method with a parameter that can also be null or undefined
// T of Undefinable<T> must be nullable
void MethodWithUndefinableParams(string varName, Undefinable<bool?>? window)
{
    JS.Set(varName, window);
}

bool? w = false;
// test to show the value is passed normally
MethodWithUndefinableParams("_willBeDefined2", w);
bool? r = JS.Get<bool?>("_willBeDefined2");
if (r != w) throw new Exception("Unexpected result");

w = null;
// null defaults to passing as undefined
MethodWithUndefinableParams("_willBeUndefined2", w);
if (!JS.IsUndefined("_willBeUndefined2")) throw new Exception("Unexpected result");

// if you need to pass null to an Undefinable parameter use Undefinable<T?>.Null
MethodWithUndefinableParams("_willBeNull2", Undefinable<bool?>.Null);
if (JS.IsUndefined("_willBeNull2")) throw new Exception("Unexpected result");

// another way to pass undefined
MethodWithUndefinableParams("_willAlsoBeUndefined2", Undefinable<bool?>.Undefined);
if (!JS.IsUndefined("_willAlsoBeUndefined2")) throw new Exception("Unexpected result");

// Create an instance of the Window JSObject class that is revived in Javascript as undefined
var undefinedWindow = JSObject.Undefined<Window>();
// undefinedWindow is an instance of Window that is revived in Javascript as undefined
JS.Set("_undefinedWindow", undefinedWindow);
var isUndefined = JS.IsUndefined("_undefinedWindow");
// isUndefined == true here

Browser	WebWorker Status	SharedWebWorker Status
Chrome	✔	✔
MS Edge	✔	✔
Firefox	✔	✔
Chrome Android	✔	❌ (SharedWorker not supported by browser)
MS Edge Android	✔	❌ (SharedWorker not supported by browser)
Firefox Android	✔	✔

// Program.cs
...
using SpawnDev.BlazorJS;
using SpawnDev.BlazorJS.WebWorkers;

var builder = WebAssemblyHostBuilder.CreateDefault(args);
builder.RootComponents.Add<App>("#app");
builder.RootComponents.Add<HeadOutlet>("head::after");
// Add SpawnDev.BlazorJS.BlazorJSRuntime
builder.Services.AddBlazorJSRuntime();
// Add SpawnDev.BlazorJS.WebWorkers.WebWorkerService
builder.Services.AddWebWorkerService(webWorkerService =>
{
    // Optionally configure the WebWorkerService service before it is used
    // Default WebWorkerService.TaskPool settings: PoolSize = 0, MaxPoolSize = 1, AutoGrow = true
    // Below sets TaskPool max size to 2. By default the TaskPool size will grow as needed up to the max pool size.
    // Setting max pool size to -1 will set it to the value of navigator.hardwareConcurrency
    webWorkerService.TaskPool.MaxPoolSize = 2;
    // Below is telling the WebWorkerService TaskPool to set the initial size to 2 if running in a Window scope and 0 otherwise
    // This starts up 2 WebWorkers to handle TaskPool tasks as needed
    // Setting this to -1 will set the initial pool size to max pool size
    webWorkerService.TaskPool.PoolSize = webWorkerService.GlobalScope == GlobalScope.Window ? 2 : 0;
});
// Add services
builder.Services.AddSingleton<IFaceAPIService, FaceAPIService>();
builder.Services.AddSingleton<IMathsService, MathsService>();
builder.Services.AddScoped((sp) => new HttpClient { BaseAddress = new Uri(builder.HostEnvironment.BaseAddress) });
// ...

// build and Init using BlazorJSRunAsync (instead of RunAsync)
await builder.Build().BlazorJSRunAsync();

public class MyService
{
    WebWorkerService WebWorkerService;
    public MyService(WebWorkerService webWorkerService)
    {
        WebWorkerService = webWorkerService;
    }
    string WorkerMethod(string input)
    {
        return $"Hello {input} from {WebWorkerService.InstanceId}";
    }
    public async Task CallWorkerMethod()
    {
        // Call the private method WorkerMethod on this scope (normal)
        Console.WriteLine(WorkerMethod(WebWorkerService.InstanceId));

        // Call the private method WorkerMethod in a WebWorker thread using an Expression
        Console.WriteLine(await WebWorkerService.TaskPool.Run(() => WorkerMethod(WebWorkerService.InstanceId)));

        // Call the private method WorkerMethod in a WebWorker thread using a Delegate
        Console.WriteLine(await WebWorkerService.TaskPool.Invoke(WorkerMethod, WebWorkerService.InstanceId));
    }
}

public class MyService
{
    WebWorkerService WebWorkerService;
    public MyService(WebWorkerService webWorkerService)
    {
        WebWorkerService = webWorkerService;
    }
    string CalledOnWindow(string input)
    {
        return $"Hello {input} from {WebWorkerService.InstanceId}";
    }
    public async Task StartedInWorker()
    {   
        // Do some work ...         
        // report back to Window (Expression example)
        // Call the private method CalledOnWindow on the Window thread using an Expression
        Console.WriteLine(await WebWorkerService.WindowTask.Run(() => CalledOnWindow(WebWorkerService.InstanceId)));

        // Do some more work ...         
        // report back to Window again (Delegate example)
        // Call the private method CalledOnWindow on the Window thread using a Delegate
        Console.WriteLine(await WebWorkerService.WindowTask.Invoke(CalledOnWindow, WebWorkerService.InstanceId));
    }
}

[Inject]
WebWorkerService workerService { get; set; }

[Inject]
IServiceProvider serviceProvider { get; set; }

// MyServiceAuto will be IMyService running in the WebWorker context if available and IMyService running in the Window context if not
IMyService MyService { get; set; }

WebWorker? webWorker { get; set; }

protected override async Task OnInitializedAsync()
{
    // GetWebWorker() will return null if workerService.WebWorkerSupported == false
    webWorker = await workerService.GetWebWorker();
    // get the WebWorker's service instance if available or this Window's service instance if not
    MyService = webWorker != null ? webWorker.GetService<IMyService>() : serviceProvider.GetService<IMyService>();
    await base.OnInitializedAsync();
}


// Create a WebWorker

[Inject]
WebWorkerService workerService { get; set; }
 
 // ...

var webWorker = await workerService.GetWebWorker();

// Call GetService<ServiceInterface> on a web worker to get a proxy for the service on the web worker.
// GetService can only be called with Interface types
var workerMathService = webWorker.GetService<IMathsService>();

// Call async methods on your worker service 
var result = await workerMathService.CalculatePi(piDecimalPlaces);

// Action types can be passed for progress reporting
var result = await workerMathService.CalculatePiWithActionProgress(piDecimalPlaces, new Action<int>((i) =>
{
    // the worker thread can call this method to report progress if desired
    piProgress = i;
    StateHasChanged();
}));

// Create or get SHaredWebWorker with the provided sharedWorkerName
var sharedWebWorker = await workerService.GetSharedWebWorker("workername");

// Just like WebWorker but shared
var workerMathService = sharedWebWorker.GetService<IMathsService>();

// Call async methods on your shared worker service
var result = await workerMathService.CalculatePi(piDecimalPlaces);

// Optionally listen for event messages
worker.OnMessage += (sender, msg) =>
{
    if (msg.TargetName == "progress")
    {
        PiProgress msgData = msg.GetData<PiProgress>();
        piProgress = msgData.Progress;
        StateHasChanged();
    }
};

// From SharedWebWorker or WebWorker threads send an event to connected parents
workerService.SendEventToParents("progress", new PiProgress { Progress = piProgress });

// Or on send an event to a connected worker
webWorker.SendEvent("progress", new PiProgress { Progress = piProgress });

public class ProcessFrameResult : IDisposable
{
    [WorkerTransfer(false)]
    public ArrayBuffer? ArrayBuffer { get; set; }
    public byte[]? HomographyBytes { get; set; }
    public void Dispose(){
        ArrayBuffer?.Dispose();
    }
}

[return: WorkerTransfer(false)]
public async Task<ProcessFrameResult?> ProcessFrame([WorkerTransfer(false)] ArrayBuffer? frameBuffer, int width, int height, int _canny0, int _canny1, double _needlePatternSize)
{
    var ret = new ProcessFrameResult();
    // ...
    return ret;
}

importScripts('_content/SpawnDev.BlazorJS.WebWorkers/spawndev.blazorjs.webworkers.js');

var builder = WebAssemblyHostBuilder.CreateDefault(args);
builder.RootComponents.Add<App>("#app");
builder.RootComponents.Add<HeadOutlet>("head::after");
// SpawnDev.BlazorJS
builder.Services.AddBlazorJSRuntime();
// SpawnDev.BlazorJS.WebWorkers
builder.Services.AddWebWorkerService();
// Register a ServiceWorker handler (AppServiceWorker here) that inherits from ServiceWorkerEventHandler
builder.Services.RegisterServiceWorker<AppServiceWorker>();
// Or Unregister the ServiceWorker if no longer desired
//builder.Services.UnregisterServiceWorker();
// SpawnDev.BlazorJS startup (replaces RunAsync())
await builder.Build().BlazorJSRunAsync();

public class AppServiceWorker : ServiceWorkerEventHandler
{
    public AppServiceWorker(BlazorJSRuntime js, ServiceWorkerConfig serviceWorkerConfig) : base(js, serviceWorkerConfig)
    {

    }

    // called before any ServiceWorker events are handled
    protected override async Task OnInitializedAsync()
    {
        // This service may start in any scope. This will be called before the app runs.
        // If JS.IsWindow == true be careful not stall here.
        // you can do initialization based on the scope that is running
        Log("GlobalThisTypeName", JS.GlobalThisTypeName);
    }

    protected override async Task ServiceWorker_OnInstallAsync(ExtendableEvent e)
    {
        Log($"ServiceWorker_OnInstallAsync");
        _ = ServiceWorkerThis!.SkipWaiting();   // returned task can be ignored
    }

    protected override async Task ServiceWorker_OnActivateAsync(ExtendableEvent e)
    {
        Log($"ServiceWorker_OnActivateAsync");
        await ServiceWorkerThis!.Clients.Claim();
    }

    protected override async Task<Response> ServiceWorker_OnFetchAsync(FetchEvent e)
    {
        Log($"ServiceWorker_OnFetchAsync", e.Request.Method, e.Request.Url);
        Response ret;
        try
        {
            ret = await JS.Fetch(e.Request);
        }
        catch (Exception ex)
        {
            ret = new Response(ex.Message, new ResponseOptions { Status = 500, StatusText = ex.Message, Headers = new Dictionary<string, string> { { "Content-Type", "text/plain" } } });
            Log($"ServiceWorker_OnFetchAsync failed: {ex.Message}");
        }
        return ret;
    }

    protected override async Task ServiceWorker_OnMessageAsync(ExtendableMessageEvent e)
    {
        Log($"ServiceWorker_OnMessageAsync");
    }

    protected override async Task ServiceWorker_OnPushAsync(PushEvent e)
    {
        Log($"ServiceWorker_OnPushAsync");
    }

    protected override void ServiceWorker_OnPushSubscriptionChange(Event e)
    {
        Log($"ServiceWorker_OnPushSubscriptionChange");
    }

    protected override async Task ServiceWorker_OnSyncAsync(SyncEvent e)
    {
        Log($"ServiceWorker_OnSyncAsync");
    }

    protected override async Task ServiceWorker_OnNotificationCloseAsync(NotificationEvent e)
    {
        Log($"ServiceWorker_OnNotificationCloseAsync");
    }

    protected override async Task ServiceWorker_OnNotificationClickAsync(NotificationEvent e)
    {
        Log($"ServiceWorker_OnNotificationClickAsync");
    }
}

LostBeard/SpawnDev.BlazorJS.WebWorkersv2.2.83

Get Started

Readme

NuGet

SpawnDev.BlazorJS

Supported .Net Versions

Features:

Issues and Feature requests

BlazorJSRuntime

IMPORTANT NOTE - Async vs Sync Javascript calls

IJSInProcessObjectReference extended

JSEventCallback

JSEventCallback arguments are optional

Action and Func serialization

Callback

IJSObject Interface

JSObject Base Class

Promise

Custom JSObjects

Union

Use the Union<T1, T2, ...> type with method parameters for strong typing while allowing unrelated types just like in TypeScript.

Undefinable

Use Undefinable<T> type to pass undefined to Javascript

SpawnDev.BlazorJS.WebWorkers

WebWorkerService.TaskPool

Supported Calling Conventions

WebWorkerService.WindowTask

WebWorker

SharedWebWorker

Send events

Worker Transferable JSObjects

Transferable JSObject types. Source MDN

ServiceWorker

wwwroot/service-worker.js

Program.cs

AppServiceWorker.cs

IDisposable

Support