要在Blazor WebAssembly应用程序中实现此功能，您可以使用C＃中的OnBeforeUnload事件，该事件会在用户尝试离开具有未保存更改的网页时触发。

下面是一个示例组件，它将响应OnBeforeUnload事件并提示用户在离开具有未保存更改的网页之前保存更改：

@page "/example"
@implements IDisposable

@inject IJSRuntime jsRuntime


    
Example Page
    
Unsaved Changes: @unsavedChanges


@code {
    private bool unsavedChanges = false;
    private bool hasNavigated = false;

    protected override void OnInitialized()
    {
        jsRuntime.InvokeVoidAsync("window.addEventListener", "beforeunload", new DotNetObjectRef(this, jsRuntime));
    }

    [JSInvokable]
    public void OnBeforeUnload()
    {
        if (unsavedChanges && !hasNavigated)
        {
            jsRuntime.InvokeVoidAsync("confirm", "You have unsaved changes. Are you sure you want to leave this page?");
        }
    }

    protected override void OnNavigating(NavigationEventArgs args)
    {
        if (unsavedChanges && !hasNavigated && !args.Cancel)
        {
            args.Cancel = true;
            jsRuntime.InvokeVoidAsync("confirm", "You have unsaved changes. Are you sure you want to navigate away from this page?");
        }
        else
        {
            hasNavigated = true;
        }
    }

    private void SaveChanges()
    {
        // Save changes logic here
        unsavedChanges = false;
    }

    private void UnsavedChangesDetected()
    {
        unsavedChanges = true;
    }

    public void Dispose()
    {
        jsRuntime.InvokeVoidAsync("window.removeEventListener", "beforeunload", new DotNetObjectRef(this, jsRuntime));
    }
}

这个示例组件演示了如何在Blazor WebAssembly应用程序中使用OnBeforeUnload事件来提示用户保存未保存的更改。在OnBeforeUnload方法中，如果有未保存的更改并且用户尚未导航到另一个页面，则会弹出确认对话框。在OnNavigating方法中，如果有未保存的更改并且用户尚未导航到另一页，则会取消导航并弹出确认对话框。

此解决方法