Even experienced developers hit the same Blazor WASM pitfalls. Here are the most common and exactly how to avoid them.

1. Not Calling StateHasChanged After External Updates

When state changes outside Blazor's event cycle (timers, SignalR), the UI won't update. Fix: call await InvokeAsync(StateHasChanged).

2. Memory Leaks from Event Subscriptions

Subscribing to AppState's OnChange without unsubscribing causes leaks. Fix: implement IDisposable and unsubscribe in Dispose().

3. Mutating Parameters Directly

Modifying a [Parameter] property directly breaks one-way data flow. Fix: use EventCallback to notify the parent.

4. Calling JS Interop Too Early

JS interop fails if called before OnAfterRenderAsync(firstRender: true). Always place JS calls inside the firstRender guard.

5. Null JSON Responses

GetFromJsonAsync returns null on 204 or empty body. Always null-coalesce: data = await Http.GetFromJsonAsync<List<T>>(url) ?? new();

6. Forgetting Routing Fallback on Deployment

Refreshing on any non-root URL returns 404 unless the server returns index.html for all routes.

Reference:

Wikipedia: Anti-Pattern

https://en.wikipedia.org/wiki/Anti-pattern