WebAssembly Memory Management

In this lesson, you will learn how to monitor memory consumption in Blazor WebAssembly to keep your long-running sessions performant and free from leaks.

Understanding the WASM Heap

Unlike server-side code, Blazor WebAssembly runs inside a sandboxed browser environment with a finite heap. Because the .NET Garbage Collector (GC) runs inside the WebAssembly runtime, it isn't always aware of external browser resources like large JavaScript objects or DOM elements. If you allocate memory in C# and link it to the browser via interop, the GC might not collect the C# object because it still holds a reference, leading to a "memory leak" that slows down the user's browser.

Preventing Leaks with IDisposable

The most effective way to prevent leaks in Blazor is to proactively clean up resources when a component is destroyed. If you subscribe to events or initialize JavaScript references, you must implement IDisposable (or IAsyncDisposable).

@implements IAsyncDisposable
@inject IJSRuntime JS

@code {
    private IJSObjectReference? _module;

    protected override async Task OnAfterRenderAsync(bool firstRender)
    {
        if (firstRender)
        {
            _module = await JS.InvokeAsync<IJSObjectReference>("import", "./js/script.js");
        }
    }

    public async ValueTask DisposeAsync()
    {
        if (_module is not null)
        {
            // Explicitly release the JS reference to free memory
            await _module.DisposeAsync();
        }
    }
}

Monitoring Memory

You can monitor your application's footprint using the browser's Memory tab in Developer Tools. For a more programmatic approach, you can track the current heap usage by checking GC.GetTotalMemory(false). If you notice the memory graph rising in a "sawtooth" pattern that never fully returns to a baseline after navigating away from a page, you likely have an object (like a service or an event handler) that is still being referenced in a static list or a long-lived dependency injection scope.

Always nullify large arrays or collection references once your component's work is finished to give the GC a helping hand in clearing the heap.

Key Takeaway: To prevent memory leaks in Blazor WebAssembly, always implement IAsyncDisposable to explicitly release interop references and ensure event handlers are unsubscribed when a component is removed from the UI.