Support the addTelemetryInitializer boolean delegate

[jacobjmarks]

The addTelemetryInitializer function defines the following signature:

public addTelemetryInitializer(telemetryInitializer: (item: ITelemetryItem) => boolean | void)

[...] If one of the telemetry initializers returns false or throws an error, then the telemetry item will not be sent.

I don't believe there currently exists a way to utilise this boolean delegate such that telemetry items can be conditionally excluded or otherwise handled. This would be extremely useful.

I realise there may be JS interop limitations which immediately prevent this capability (serialization of a Func<> argument), but raising this issue in the hopes that some level of equivalence could be achieved.

[IvanJosipovic]

I attempted to solve this a few times, the main issue is the call is synchronous and JSInterop must be async. I was not able to get this to work :(

[jacobjmarks]

I don't understand how sync/async issues could be blocking this; would you mind giving some more detail?

[IvanJosipovic]

App Insights calls the telemetryInitializer synchronously, in that method, we need to call JSInterop into Blazor, this call has to be done async.

I had it implemented in my v3 pr, but it didn't work.

BlazorApplicationInsights/src/BlazorApplicationInsights/ApplicationInsights.cs

Line 68 in bb2d22b

public async Task AddTelemetryInitializer(Func<TelemetryItem, bool> telemetryInitializer)

BlazorApplicationInsights/src/BlazorApplicationInsights/Models/TelemetryInitializer.cs

Line 6 in bb2d22b

internal class TelemetryInitializer

The issue is here, where we inject the initializer, it has to be async but it doesn't work.

BlazorApplicationInsights/src/BlazorApplicationInsights/wwwroot/JsInterop.js

Line 3 in bb2d22b

appInsights.addTelemetryInitializer(async (telemetryItem) => {

[jacobjmarks]

I see. From the documentation, .NET provides a synchronous version of the invocation method: DotNet.invokeMethod() (see here). Has this been explored?

[IvanJosipovic]

I haven't as it only works on WASM, but that would likely work.

If the WASM limitation is fine, I'd happily take a PR. We should add a new method "AddWASMTelemetryInitializer" or something so its clear it only works on WASM.