Thank you for perusing my Blazor C# Source Generators repository. I'd really appreciate a ⭐ if you find this interesting.
A C# source generator that creates extensions methods on the Blazor WebAssembly JavaScript implementation of the IJSInProcessRuntime type. This library provides several NuGet packages:
Consider the SynchronousLocalStorageExtensions.cs C# file:
// Copyright (c) David Pine. All rights reserved.
// Licensed under the MIT License.
namespace Microsoft.JSInterop;
/// <summary>
/// Source generated extension methods on the <see cref="IJSInProcessRuntime"/> implementation.
/// </summary>
[JSAutoGenericInterop(
TypeName = "Storage",
Implementation = "window.localStorage",
Url = "https://developer.mozilla.org/docs/Web/API/Window/localStorage",
GenericMethodDescriptors = new[]
{
"getItem",
"setItem:value"
})]
internal static partial class SynchronousLocalStorageExtensions
{
}
This code designates itself into the Microsoft.JSInterop namespace, making all of the source generated extensions available to anyone consumer who uses types from this namespace. It uses the JSAutoInterop to specify:
Implementation = "window.localStorage": expresses how to locate the implementation of the specified type from the globally scoped window object, this is the localStorage implementation.
Url: sets the URL for the implementation.
GenericMethodDescriptors: Defines the methods that should support generics as part of their source-generation. The localStorage.getItem is specified to return a generic TResult type, and the localStorage.setItem has its parameter with a name of value specified as a generic TArg type.
The generic method descriptors syntax is:
"methodName" for generic return type and "methodName:parameterName" for generic parameter type.
The file needs to define an extension class and needs to be partial, for example; internal static partial class. Decorating the class with the JSAutoInterop (or `JSAutoGenericInterop) attribute will source generate the following C# code:
// Copyright (c) David Pine. All rights reserved.
// Licensed under the MIT License:
// https://github.com/IEvangelist/blazorators/blob/main/LICENSE
// Auto-generated by blazorators.
using Blazor.Serialization.Extensions;
using System.Text.Json;
#nullable enable
namespace Microsoft.JSInterop;
internal static partial class SynchronousLocalStorageExtensions
{
/// <summary>
/// Source generated extension method implementation of <c>window.localStorage.clear</c>.
/// <a href="https://developer.mozilla.org/docs/Web/API/Storage/clear"></a>
/// </summary>
public static void Clear(
this IJSInProcessRuntime javaScript) =>
javaScript.InvokeVoid("window.localStorage.clear");
/// <summary>
/// Source generated extension method implementation of <c>window.localStorage.getItem</c>.
/// <a href="https://developer.mozilla.org/docs/Web/API/Storage/getItem"></a>
/// </summary>
public static TResult? GetItem<TResult>(
this IJSInProcessRuntime javaScript,
string key,
JsonSerializerOptions? options = null) =>
javaScript.Invoke<string?>(
"window.localStorage.getItem",
key)
.FromJson<TResult>(options);
/// <summary>
/// Source generated extension method implementation of <c>window.localStorage.key</c>.
/// <a href="https://developer.mozilla.org/docs/Web/API/Storage/key"></a>
/// </summary>
public static string? Key(
this IJSInProcessRuntime javaScript,
double index) =>
javaScript.Invoke<string?>(
"window.localStorage.key",
index);
/// <summary>
/// Source generated extension method implementation of <c>window.localStorage.removeItem</c>.
/// <a href="https://developer.mozilla.org/docs/Web/API/Storage/removeItem"></a>
/// </summary>
public static void RemoveItem(
this IJSInProcessRuntime javaScript,
string key) =>
javaScript.InvokeVoid(
"window.localStorage.removeItem",
key);
/// <summary>
/// Source generated extension method implementation of <c>window.localStorage.setItem</c>.
/// <a href="https://developer.mozilla.org/docs/Web/API/Storage/setItem"></a>
/// </summary>
public static void SetItem<TArg>(
this IJSInProcessRuntime javaScript,
string key,
TArg value,
JsonSerializerOptions? options = null) =>
javaScript.InvokeVoid(
"window.localStorage.setItem",
key,
value.ToJson(options));
/// <summary>
/// Source generated extension method implementation of <c>window.localStorage.length</c>.
/// <a href="https://developer.mozilla.org/docs/Web/API/Storage/length"></a>
/// </summary>
public static double Length(
this IJSInProcessRuntime javaScript) =>
javaScript.Invoke<double>(
"eval", "window.localStorage.length");
}
These internal extension methods rely on the IJSInProcessRuntime to perform JavaScript interop. From the given TypeName and corresponding Implementation, the following code is also generated:
IStorage.g.cs: The interface for the corresponding Storage Web API surface area.
LocalStorge.g.cs: The internal implementation of the IStorage interface.
LocalStorageServiceCollectionExtensions.g.cs: Extension methods to add the IStorage service to the dependency injection IServiceCollection.
Finally, here is the source generated service collection extension methods:
using Microsoft.JSInterop;
namespace Microsoft.Extensions.DependencyInjection;
/// <summary></summary>
public static class LocalStorageServiceCollectionExtensions
{
/// <summary>
/// Adds the <see cref="IStorage" /> service to the service collection.
/// </summary>
public static IServiceCollection AddLocalStorageServices(
this IServiceCollection services) =>
services.AddSingleton<IJSInProcessRuntime>(serviceProvider =>
(IJSInProcessRuntime)serviceProvider.GetRequiredService<IJSRuntime>())
.AddSingleton<IStorage, LocalStorage>();
}
Putting this all together, the Blazor.LocalStorage.WebAssembly NuGet package is actually only 20 lines of code, and it generates full DI-ready services with JavaScript interop.
The Blazor.LocalStorage.Server package, generates extensions on the IJSRuntime type.
// Copyright (c) David Pine. All rights reserved.
// Licensed under the MIT License.
namespace Microsoft.JSInterop;
/// <summary>
/// Source generated extension methods on the <see cref="IJSRuntime"/> implementation.
/// </summary>
[JSAutoInterop(
TypeName = "Storage",
Implementation = "window.localStorage",
HostingModel = BlazorHostingModel.Server,
OnlyGeneratePureJS = true,
Url = "https://developer.mozilla.org/docs/Web/API/Window/localStorage")]
public static partial class AsynchronousLocalStorageExtensions
{
}
Generates the following:
// Copyright (c) David Pine. All rights reserved.
// Licensed under the MIT License:
// https://github.com/IEvangelist/blazorators/blob/main/LICENSE
// Auto-generated by blazorators.
using System.Threading.Tasks;
#nullable enable
namespace Microsoft.JSInterop;
public static partial class AsynchronousLocalStorageExtensions
{
/// <summary>
/// Source generated extension method implementation of <c>window.localStorage.clear</c>.
/// <a href="https://developer.mozilla.org/docs/Web/API/Storage/clear"></a>
/// </summary>
public static ValueTask ClearAsync(
this IJSRuntime javaScript) =>
javaScript.InvokeVoidAsync("window.localStorage.clear");
/// <summary>
/// Source generated extension method implementation of <c>window.localStorage.getItem</c>.
/// <a href="https://developer.mozilla.org/docs/Web/API/Storage/getItem"></a>
/// </summary>
public static ValueTask<string?> GetItemAsync(
this IJSRuntime javaScript,
string key) =>
javaScript.InvokeAsync<string?>(
"window.localStorage.getItem",
key);
/// <summary>
/// Source generated extension method implementation of <c>window.localStorage.key</c>.
/// <a href="https://developer.mozilla.org/docs/Web/API/Storage/key"></a>
/// </summary>
public static ValueTask<string?> KeyAsync(
this IJSRuntime javaScript,
double index) =>
javaScript.InvokeAsync<string?>(
"window.localStorage.key",
index);
/// <summary>
/// Source generated extension method implementation of <c>window.localStorage.removeItem</c>.
/// <a href="https://developer.mozilla.org/docs/Web/API/Storage/removeItem"></a>
/// </summary>
public static ValueTask RemoveItemAsync(
this IJSRuntime javaScript,
string key) =>
javaScript.InvokeVoidAsync(
"window.localStorage.removeItem",
key);
/// <summary>
/// Source generated extension method implementation of <c>window.localStorage.setItem</c>.
/// <a href="https://developer.mozilla.org/docs/Web/API/Storage/setItem"></a>
/// </summary>
public static ValueTask SetItemAsync(
this IJSRuntime javaScript,
string key,
string value) =>
javaScript.InvokeVoidAsync(
"window.localStorage.setItem",
key,
value);
/// <summary>
/// Source generated extension method implementation of <c>window.localStorage.length</c>.
/// <a href="https://developer.mozilla.org/docs/Web/API/Storage/length"></a>
/// </summary>
public static ValueTask<double> LengthAsync(
this IJSRuntime javaScript) =>
javaScript.InvokeAsync<double>(
"eval", "window.localStorage.length");
}
Notice, that since the generic method descriptors are not added generics are not supported. This is not yet implemented as I've been focusing on WebAssembly scenarios.
Using the Blazor.LocalStorage.WebAssembly package 📦
The Blazor.LocalStorage.WebAssembly package is a WebAssembly specific implementation of the localStorage Web API that has been source generated. The example above is the result of this published package.
This package exposes a convenience extension method on the IServiceCollection type, named AddWebAssemblyLocalStorage. Calling this will expose the IJSInProcessRuntime as a dependency injection service type as a scoped lifetime. Consider the following Program.cs C# file for an example Blazor WebAssembly template project:
using Blazor.ExampleConsumer;
using Microsoft.AspNetCore.Components.Web;
using Microsoft.AspNetCore.Components.WebAssembly.Hosting;
var builder = WebAssemblyHostBuilder.CreateDefault(args);
builder.RootComponents.Add<App>("#app");
builder.RootComponents.Add<HeadOutlet>("head::after");
builder.Services.AddScoped(
sp => new HttpClient
{
BaseAddress = new Uri(builder.HostEnvironment.BaseAddress)
});
// Adds the IJSInProcessRuntime type to DI.
builder.Services.AddWebAssemblyLocalStorage();
await builder.Build().RunAsync();
Then, in your components you can consume this as you would any other service type. Consider the Counter.razor file:
I was hoping to use the TypeScript lib.dom.d.ts bits as input. This input would be read, parsed, and cached within the generator. The generator code would be capable of generating extension methods on the IJSRuntime. Additionally, the generator will create object graphs from the well know web APIs.
Using the lib.dom.d.ts file, we could hypothetically parse various TypeScript type definitions. These definitions could then be converted to C# counterparts. While I realize that not all TypeScript is mappable to C#, there is a bit of room for interpretation.
Consider the following type definition:
/**
An object can programmatically obtain the position of the device.
It gives Web content access to the location of the device. This allows
a Web site or app to offer customized results based on the user's location.
*/
interface Geolocation {
clearWatch(watchId: number): void;
getCurrentPosition(
successCallback: PositionCallback,
errorCallback?: PositionErrorCallback | null,
options?: PositionOptions): void;
watchPosition(
successCallback: PositionCallback,
errorCallback?: PositionErrorCallback | null,
options?: PositionOptions): number;
}
Ideally, I would like to be able to define a C# class such as this:
[JSAutoInterop(
TypeName = "Geolocation",
PathFromWidow = "window.navigator.geolocation",
Url = "https://developer.mozilla.org/en-US/docs/Web/API/Geolocation_API",
OnlyGeneratePureJS = false)]
public static partial class GeolocationExtensions { }
The source generator will expose the JSAutoInteropAttribute, and consuming libraries will decorate their classes with it. The generator code will see this class, and use the TypeName from the attribute to find the corresponding type to implement.
With the type name, the generator will generate the corresponding methods, and return types. The method implementations will be extensions of the IJSRuntime.
The following is an example resulting source generated GeolocationExtensions object:
using Microsoft.JSInterop;
namespace Microsoft.JSInterop.Extensions;
public static partial class GeolocationExtensions
{
/// <summary>
/// See <a href="https://developer.mozilla.org/en-US/docs/Web/API/Geolocation/getCurrentPosition"></a>.
/// </summary>
public static ValueTask GetCurrentPositionAsync<T>(
this IJSRuntime jsRuntime,
T dotnetObject,
string successMethodName,
string? errorMethodName = null,
PositionOptions? options = null)
where T : class
{
return jsRuntime.InvokeVoidAsync(
"blazorator.getCurrentLocation",
DotNetObjectReference.Create(dotnetObject),
successMethodName,
errorMethodName,
options
);
}
/// <summary>
/// See <a href="https://developer.mozilla.org/en-US/docs/Web/API/Geolocation/watchPosition"></a>
/// </summary>
public static ValueTask<double> WatchPositionAsync<T>(
this IJSRuntime jsRuntime,
T dotnetObject,
string successMethodName,
string? errorMethodName = null,
PositionOptions? options = null)
where T : class
{
return jsRuntime.InvokeAsync<double>(
"blazorator.watchPosition",
DotNetObjectReference.Create(dotnetObject),
successMethodName,
errorMethodName,
options
);
}
/// <summary>
/// See <a href="https://developer.mozilla.org/en-US/docs/Web/API/Geolocation/clearWatch"></a>
/// </summary>
public ValueTask ClearWatchAsync(this IJSRuntime jsRuntime, double id)
{
return jsRuntime.InvokevoidAsync(
"navigator.geolocation.clearWatch", id
);
}
}
The generator will also produce the corresponding APIs object types. For example, the Geolocation API defines the following:
PositionOptions
GeolocationCoordinates
GeolocationPosition
GeolocationPositionError
using System.Text.Json.Serialization;
namespace Microsoft.JSInterop.Extensions;
/// <summary>
/// See <a href="https://developer.mozilla.org/en-US/docs/Web/API/GeolocationPosition"></a>
/// </summary>
public record GeolocationPosition(
[property: JsonPropertyName("coords")] GeolocationCoordinates Coordinates,
[property: JsonPropertyName("timestamp")] DOMTimeStamp TimeStamp
);
/// <summary>
/// See <a href="https://developer.mozilla.org/en-US/docs/Web/API/GeolocationCoordinates"></a>
/// </summary>
public record GeolocationCoordinates(
[property: JsonPropertyName("latitude")] double Latitude,
[property: JsonPropertyName("longitude")] double Longitude,
[property: JsonPropertyName("altitude")] double Altitude,
[property: JsonPropertyName("altitudeAccuracy")] double? AltitudeAccuracy,
[property: JsonPropertyName("heading")] double? Heading,
[property: JsonPropertyName("speed")] double Speed
);
/// <summary>
/// See <a href="https://developer.mozilla.org/en-US/docs/Web/API/GeolocationPositionError"></a>
/// </summary>
public record GeolocationPositionError(
[property: JsonPropertyName("code")] short Code,
[property: JsonPropertyName("message")] string Message
);
// Additional models omitted for brevity...
In addition to this GeolocationExtensions class being generated, the generator will also generate a bit of JavaScript. Some methods cannot be directly invoked as they define callbacks. The approach the generator takes is to delegate callback methods on a given T instance, with the JSInvokable attribute. Our generator should also warn when the corresponding T instance doesn't define a matching method name that is also JSInvokable.
const getCurrentLocation =
(dotnetObj, successMethodName, errorMethodName, options) =>
{
if (navigator && navigator.geolocation) {
navigator.geolocation.getCurrentPosition(
(position) => {
dotnetObj.invokeMethodAsync(
successMethodName, position);
},
(error) => {
dotnetObj.invokeMethodAsync(
errorMethodName, error);
},
options);
}
};
// Other implementations omitted for brevity...
// But we'd also define a "watchPosition" wrapper.
// The "clearWatch" is a straight pass-thru, no wrapper needed.
window.blazorator = {
getCurrentLocation,
watchPosition
};
The resulting JavaScript will have to be exposed to consuming projects. Additionally, consuming projects will need to adhere to extension method consumption semantics. When calling generated extension methods that require .NET object references of type T, the callback names should be marked with JSInvokable and the nameof operator should be used to ensure names are accurate. Consider the following example consuming Blazor component:
using Microsoft.AspNetCore.Components;
using Microsoft.JSInterop;
using Microsoft.JSInterop.Extensions;
namespace Example.Components;
// This is the other half of ConsumingComponent.razor
public sealed partial class ConsumingComponent
{
[Inject]
public IJSRuntime JavaScript { get; set; }
protected override async Task OnAfterRenderAsync(bool firstRender)
{
if (firstRender)
{
await JavaScript.GetCurrentPositionAsync(
this,
nameof(OnCoordinatesPermitted),
nameof(OnErrorRequestingCoordinates));
}
}
[JSInvokable]
public async Task OnCoordinatesPermitted(
GeolocationPosition position)
{
// TODO: consume/handle position.
await InvokeAsync(StateHasChanged);
}
[JSInvokable]
public async Task OnErrorRequestingCoordinates(
GeolocationPositionError error)
{
// TODO: consume/handle error.
await InvokeAsync(StateHasChanged);
}
}
Pseudocode and logical flow ➡️
Consumer decorates a static partial class with the JSAutoInteropAttribute.
Source generator is called:
JavaScriptInteropGenerator.Initialize
JavaScriptInteropGenerator.Execute
The generator determines the TypeName from the attribute of the contextual class.
The TypeName is used to look up the corresponding TypeScript type definition.
If found, and a valid API - attempt source generation.
Known limitations ⚠️
At the time of writing, only pure JavaScript interop is supported. It is a stretch goal to add the following (currently missing) features:
