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Blazor Interview Questions and Answers

May 30, 2023 | .NET

Are you preparing for an upcoming Blazor developer interview? Dive into this comprehensive guide on Blazor interview questions and answers, designed to give you the knowledge and confidence to excel in your interview and land the job.

In this article, we’ve rounded up crucial Blazor topics and questions you might encounter, carefully explained with examples and details to demonstrate your understanding of this powerful web framework.

Stay ahead of the curve: let’s dive into these essential Blazor interview questions that could make the difference in securing your next development opportunity.


In Blazor Server, how does the application maintain a real-time connection between the server and the client and what options are available for you to configure this connection?


In a Blazor Server application, a real-time connection between the server and the client is maintained using SignalR, an open-source library for web applications that enables real-time bi-directional communication. When a Blazor Server app is initialized, a dedicated SignalR connection is established for each individual client.

You can configure the SignalR connection using the following options:

  1. Transport: Choose between WebSockets, Server-Sent Events, and Long Polling. You can modify the transport by configuring SignalR in Startup.cs:
services.AddServerSideBlazor(config =>
    config.Transport.MaxBufferSize = 10 * 1024 * 1024; // 10MB buffer
    config.Transport.TransportType = Microsoft.AspNetCore.Http.Connections.HttpTransportType.WebSockets;
  1. MessagePack: Optimize message serialization by using MessagePack instead of the default JSON in SignalR communications. To use MessagePack, you need to add and configure the Microsoft.AspNetCore.SignalR.Protocols.MessagePack package:
    .AddHubOptions(o =>
  1. Circuit options: Configure circuit settings such as the maximum number of circuits and circuit disposal intervals:
services.AddServerSideBlazor(options =>
    options.MaxConcurrentConnections = 100;
    options.DisconnectedCircuitMaxRetained = 50;
    options.DisconnectedCircuitRetentionPeriod = TimeSpan.FromMinutes(5);
  1. Reconnection: Manage how the app reconnects after a lost connection:
CircuitOptions.DetailedErrors = true;
CircuitOptions.DisconnectedCircuitMaxRetained = 100;
CircuitOptions.DisconnectedCircuitRetentionPeriod = TimeSpan.FromSeconds(30);

How can you enable server-side pre-rendering in a Blazor WebAssembly application, and what benefits does it provide?


To enable server-side pre-rendering in a Blazor WebAssembly application, you need to follow these steps:

  1. In the server project (e.g., ASP.NET Core), open the _Host.cshtml file.
  2. Replace the <app> element with the following Razor code:
<component type="typeof(App)" render-mode="ServerPrerendered" />

By pre-rendering the app on the server, it generates the initial HTML markup and sends it to the client, making the following benefits possible:

  1. Faster initial load times: Pre-rendered apps have a faster perceived initial load time as the browser displays the pre-rendered content before loading the entire app.
  2. Better search engine optimization (SEO): Pre-rendering makes it easier for search engines to crawl and index the application’s content, as the content is already available in the HTML markup.
  3. Improved accessibility: Pre-rendering can improve the experience for users who have slow internet connections or slow devices, by rendering content as quickly as possible, even before the app is ready to receive input.
  4. Compilation error handling: A pre-rendered app can show error messages during development, which may help diagnose issues related to compilation, dependencies, etc.

However, it’s important to note that server-side pre-rendering can also increase server load and may potentially cause issues related to concurrency if not handled carefully.

What is the primary difference between using an EventCallback and a regular C# event when handling events in Blazor components?


The primary difference between EventCallback and a regular C# event in Blazor components is that EventCallback automatically handles UI updates and component re-rendering properly, while regular C# events do not.

Blazor’s EventCallback:

  • Triggers component re-rendering once the callback is invoked.
  • Participates in the Blazor event handling system, providing efficient and automatic error handling.
  • Automatically validates the event handlers’ compatibility with asynchronous processing.
  • Helps prevent common issues, such as unhandled exceptions, by following the proper error propagation mechanisms used in Blazor.

On the other hand, regular C# events:

  • Do not trigger component re-rendering automatically, requiring manual intervention when it’s necessary to update the UI.
  • Do not participate in Blazor’s event handling system, which can lead to missing error handling and potential issues.

In summary, using EventCallback is recommended for handling events in Blazor components, as it provides better integration with the Blazor framework and promotes an efficient and consistent event handling experience.

Describe the role of a RenderTreeBuilder in the Blazor component rendering process and explain how the component lifecycle is impacted by its use.


In the Blazor component rendering process, the RenderTreeBuilder is responsible for generating the virtual representation of the component’s DOM, called the render tree. The render tree is a tree-like data structure that efficiently describes the UI elements and their relationships, making it easier for Blazor to update the actual DOM in the browser.

RenderTreeBuilder is used automatically by the Blazor framework when you author components using Razor syntax. However, it can also be used to manually construct render trees in cases where components are defined using C# code.

The component lifecycle is impacted by the use of RenderTreeBuilder in the following ways:

  1. Initialization: When a component is initialized, the RenderTreeBuilder is utilized to create the initial render tree based on the component’s markup.
  2. Rendering: After the first rendering or whenever the component’s state changes (e.g., due to events or parameter updates), Blazor invokes the component’s BuildRenderTree(RenderTreeBuilder builder) method. The RenderTreeBuilder is used to generate the new render tree representing the updated UI state.
  3. Update: Blazor compares the new render tree with the previous one, calculates the minimum set of DOM updates required, and applies the updates to the browser’s actual DOM.

In summary, the RenderTreeBuilder plays a crucial role in the Blazor component rendering process and significantly impacts the component lifecycle by efficiently generating and updating the render tree during the component’s lifetime.

Explain the concept of JavaScript isolation in Blazor WebAssembly and how it helps improve the modularity and security of the application.


JavaScript isolation in Blazor WebAssembly is a feature that allows you to include and execute JavaScript files as part of a specific scoped area, such as a Razor component, without affecting other components or the global JavaScript context. This isolation promotes better modularity, maintainability, and security in your application, as it reduces the chances of conflicts and unintended side effects between different parts of your app.

JavaScript isolation is achieved by using JavaScript modules (ES6 Modules), which are files that export JavaScript objects, functions, or values that can be imported by other modules or scripts.

Here’s how JavaScript isolation in Blazor WebAssembly works:

  1. Create a JavaScript module (e.g., myScript.js) and define your JavaScript functions and objects within it. Use the export keyword to make them available for import:
export function showAlert(msg) {
  1. In your Blazor component (.razor file), use the IJSObjectReference type to define a reference to the isolated JavaScript module:
@inject IJSRuntime JSRuntime
private IJSObjectReference module;

protected override async Task OnInitializedAsync()
    module = await JSRuntime.InvokeAsync<IJSObjectReference>("import", "./myScript.js");
  1. Now, you can access the exported JavaScript functions and objects using the module reference:
private async Task ShowMessage()
    await module.InvokeVoidAsync("showAlert", "Hello from an isolated script!");

By isolating JavaScript code in this manner, you can:

  • Keep JavaScript functions and objects scope specific to individual components, preventing unintended interactions.
  • Improve maintainability by encapsulating JavaScript logic within the component that requires it.
  • Enhance security by limiting the scope and exposure of JavaScript code, making it less vulnerable to cross-scripting attacks and other security threats.

Having discussed the intricacies of JavaScript isolation in Blazor WebAssembly, we now turn to another critical aspect of working with this framework: efficiently handling large datasets.

In the following question, we’ll be exploring Blazor’s component virtualization feature and the factors to consider in order to work with large datasets more effectively.

When utilizing Blazor’s component virtualization feature, what are the factors that need to be considered to properly handle large datasets efficiently?


Blazor’s component virtualization feature allows you to render only the visible portion of a large dataset, improving performance and reducing memory usage. When implementing virtualization, consider the following factors to handle large datasets efficiently:

  1. Place the Virtualize component: Wrap the list or the element you want to render with the <Virtualize> component. The component takes care of loading and unloading items based on the user’s scroll position.
<Virtualize Items="items" Context="item">
  1. Specify item size: To optimize the loading and unloading of items, provide the item size in pixels using the ItemSize parameter. This helps the Virtualize component determine the visible items based on the scroll position.
<Virtualize Items="items" Context="item" ItemSize="50">
  1. Fetch data on-demand: When you have large datasets that cannot be loaded entirely in memory, you can use the ItemsProvider parameter to provide a method for fetching data in smaller chunks as required.
private async ValueTask<ItemsProviderResult<TItem>> LoadItems(ItemsProviderRequest request)
    // Fetch data based on the request.
<Virtualize ItemsProvider="LoadItems" Context="item">
  1. Placeholders during loading: To improve user experience, provide placeholders for items that are not yet loaded by using the Placeholder parameter in the Virtualize component.
<Virtualize Items="items" Context="item" Placeholder="@LoadingPlaceholder">

@code {
    private RenderFragment LoadingPlaceholder => (builder) =>
        builder.OpenElement(0, "div");
        builder.SetAttribute(1, "class", "loading-placeholder");
        builder.AddContent(2, "Loading...");
  1. Avoid unnecessary re-rendering: Using virtualization efficiently means minimizing unnecessary re-rendering. Ensure that components inside the Virtualize component do not cause additional re-rendering unless needed.

By keeping these factors in mind, you can properly handle large datasets efficiently by reducing the memory usage and DOM updates with the Virtualize component.

How can you implement a custom AuthenticationStateProvider in Blazor, and what are the key methods that need to be overridden to provide your own authentication logic?


AuthenticationStateProvider is an abstract class provided by Blazor that allows you to manage the authentication state in your application. To create a custom authentication state provider, follow the steps below:

  1. Create a new class that inherits from AuthenticationStateProvider.
public class CustomAuthenticationStateProvider : AuthenticationStateProvider
  1. Override the GetAuthenticationStateAsync() method. This method is responsible for returning the current authentication state as a Task<AuthenticationState> object. Implement your authentication logic within this method.
public override async Task<AuthenticationState> GetAuthenticationStateAsync()
    // Your authentication logic here.
  1. Use the NotifyAuthenticationStateChanged() method to notify subscribers whenever the authentication state changes. This method takes a task representing the new AuthenticationState.
private void NotifyStateChanged()
    var authState = GetAuthenticationStateAsync();
  1. To use your custom AuthenticationStateProvider in the app, register it in the Startup.cs file (Blazor Server) or Program.cs file (Blazor WebAssembly) by calling AddScoped() and replacing the default provider:
services.AddScoped<AuthenticationStateProvider, CustomAuthenticationStateProvider>();

By creating a custom AuthenticationStateProvider, you can implement your own authentication logic, manage user authentication states, and propagate changes throughout the application.

In a Blazor WebAssembly app, how can you optimize the application’s startup performance, and what steps can be taken to reduce the initial download size?


Optimizing startup performance and reducing the initial download size in a Blazor WebAssembly app can be achieved through the following steps:

  1. Linker configuration: The .NET IL linker tool is used in Blazor WebAssembly projects to trim unused code during the build process. You can configure the linker to be more aggressive by modifying the PublishTrimmed and TrimMode properties in the .csproj file:

However, aggressive trimming may cause runtime errors if the linker removes required dependencies. Test your app thoroughly after making changes.

  1. Precompress content: Enable the precompression of static files during the publish process by adding the following line in the .csproj file:

This will generate compressed versions of the static files in the wwwroot directory (e.g., .br, .gz files), which can be served by your web server, reducing the initial download size.

  1. Lazy-load assemblies: Split your application into smaller projects and use the OnNavigateAsync method to lazy-load these assemblies as your users navigate between pages. This defers the loading of assemblies to when they are actually needed.
protected override async Task OnNavigateAsync(NavigationContext navigationContext)
    await JSRuntime.InvokeVoidAsync("import", "./additionalContent.js").AsTask();
  1. Reduce external dependencies: Evaluate the external dependencies used in your project, remove any unnecessary ones, and use lighter alternatives when possible.
  2. Optimize images and resources: Compress and optimize images, fonts, and other static resources. You can use tools like ImageSharp for image optimization and WebOptimizer for bundling and minification of CSS and JS files.
  3. Server-side rendering (SSR): Although not directly related to reducing the initial download size, SSR can improve the perceived startup performance by sending pre-rendered HTML to the client.

By following these steps, you can optimize the startup performance and reduce the initial download size of your Blazor WebAssembly app, improving the user experience.

How does using a CascadingValue component in Blazor help manage the state of your application, and what are some common use cases for it?


Using a CascadingValue component in Blazor helps manage the state of your application by providing a way to share data across a component hierarchy without needing to pass properties explicitly. The CascadingValue component essentially creates a scoped context or service that can be consumed by descendant components without being explicitly passed through intermediate components.

Here are some common use cases for the CascadingValue component:

  1. Shared theming: If your application has a shared theme, you can use a CascadingValue component to change the theme dynamically across all components without having to pass the theme value through properties.
  2. User authentication: Store and share user authentication data (e.g., user roles, claims, and other profile information) across descendant components without requiring each component to take authentication information as a parameter.
  3. Localization: CascadingValue can be employed to pass information about the current culture or language settings, allowing components to update their localization accordingly.
  4. Global app settings: Provide application-wide settings or configuration data that are used consistently across multiple components without passing them individually through properties.

Here’s an example of using the CascadingValue component:

<CascadingValue Value="mySharedValue">
  <ChildComponent />

And in the child component:

@inherits ComponentBase
[CascadingParameter] private string mySharedValue { get; set; }

<p>Shared Value: @mySharedValue</p>

By using the CascadingValue component, you can greatly simplify state management in your Blazor applications and improve code readability and maintainability.

What are the differences between the RenderMode.Server and RenderMode.ServerPrerendered in Blazor applications, and how does the choice affect component rendering?


In Blazor applications, RenderMode is an enumeration used to determine how a component is rendered within the hosting page. The main differences between RenderMode.Server and RenderMode.ServerPrerendered are:

  • RenderMode.Server: With this render mode, Blazor components are rendered entirely on the server, and user interactions with the components are handled through a real-time connection (e.g., SignalR). In this mode, there is no initial HTML markup generated, and the component’s output is only visible once the Blazor application is initialized and the connection is established. This mode provides faster update cycles and smaller bundle sizes but can increase server load.
  • RenderMode.ServerPrerendered: In this render mode, the components on the hosting page are pre-rendered on the server, generating an initial HTML markup that is sent to the client. As a result, the initial perceived load time is faster, as the user can see the pre-rendered content before the Blazor application is fully initialized. After the app is initialized, user interactions are handled similarly to the RenderMode.Server mode. This mode offers improved startup performance and better search engine optimization (SEO) at the cost of increased server load and potentially larger initial download size.

Choosing between RenderMode.Server and RenderMode.ServerPrerendered depends on your application’s requirements and priorities. If startup performance and SEO are more important, then RenderMode.ServerPrerendered is an appropriate choice. If reducing server load and optimizing runtime performance is a priority, you may prefer RenderMode.Server.

As we’ve dissected the differences between RenderMode.Server and RenderMode.ServerPrerendered, it’s evident that the choice between these modes can significantly impact component rendering.

Next, we will take a closer look at the practicality of using custom CSS isolation files in Blazor components and how to tackle conflicts between component styles.

How do you implement and use a custom CSS isolation file in a Blazor component and what happens when multiple components have conflicting styles?


CSS isolation in Blazor allows you to scope styles to specific components, preventing styles from leaking into other components and making it easier to manage the CSS in your application.

To implement and use a custom CSS isolation file in a Blazor component:

  1. Create a CSS file with the same name as the component file but add the .css extension. For example, if your component is named MyComponent.razor, create a file called MyComponent.razor.css.
  2. Write your styles in the newly created CSS file.
  3. When you build your application, Blazor generates a unique scope identifier for each component and appends it to the component’s HTML elements and corresponding CSS rules. This makes the styles specific to the component, avoiding conflicts with other components.

When multiple components have conflicting styles, CSS isolation prevents the styles from affecting other components. Each component’s styles are properly scoped, and the unique identifiers generated by Blazor ensure that the styles apply only to the intended component.

If you need to override the styles or apply global styles, you can create a non-isolated CSS file without the .razor prefix and include it in your application’s index.html (Blazor WebAssembly) or _Host.cshtml (Blazor Server) file.

Explain the process of implementing server-side pagination using Blazor Server, and what considerations need to be made for its efficient execution.


Server-side pagination is a technique to reduce the amount of data sent to the client by splitting the data into smaller chunks (pages) and loading only the required page. Below is an overview of how to implement server-side pagination using Blazor Server:

  1. Backend: Create an API or a service method that accepts pagination parameters, such as pageIndex and pageSize. This method should query the required data based on the pagination parameters and return it along with the total number of records.
public async Task<(IEnumerable<TData> Data, int Total)> GetPaginatedDataAsync(int pageIndex, int pageSize)
    // Query data from data source using pageIndex and pageSize.
  1. Blazor component: Create a Blazor component to display the paginated data. In this component, request data from the backend API/service created in the previous step.
  2. UI: Add UI elements for navigating between pages, such as previous/next buttons and a page number input.
<button @onclick="PreviousPage">Previous</button>
<button @onclick="NextPage">Next</button>
<input type="number" @bind="CurrentPage" @oninput="PageNumberChanged" />
  1. Code: Create methods to handle pagination events in the component. When the user interacts with the pagination UI elements, update the pageIndex and request new data from the backend API/service.
private int CurrentPage { get; set; } = 1;

private async Task PreviousPage()
    await LoadDataAsync();

private async Task NextPage()
    await LoadDataAsync();

private async Task PageNumberChanged(ChangeEventArgs e)
    CurrentPage = Convert.ToInt32(e.Value);
    await LoadDataAsync();

private async Task LoadDataAsync()
    var (data, total) = await service.GetPaginatedDataAsync(CurrentPage - 1, PageSize);
    // Update the component's data and trigger a re-render.

When implementing server-side pagination, the following considerations should be made for efficient execution:

  1. Optimized data querying: Implement efficient data querying techniques, such as using the Take() and Skip() methods to minimize the data retrieved from the database.
  2. Debounce user input: Debounce the user input, especially when using a page number input, to prevent excessive calls to the backend API.
  3. Error handling: Implement error handling when fetching paginated data and provide a fallback UI for empty data sets or erroneous requests.
  4. User experience: Ensure smooth transitions between pages and consider implementing loading indicators during the loading of new data.

How are Blazor components’ lifecycle events affected when using a server-side Blazor application compared to a client-side Blazor WebAssembly application?


Blazor components have a common set of lifecycle events that enable you to perform tasks throughout the component’s lifecycle. However, there are some differences in how these events execute in server-side Blazor applications versus client-side Blazor WebAssembly applications:

  • OnInit/OnInitAsync: These methods are called once when the component is initialized, regardless of whether the app is running on the server or the client.
  • OnParametersSet/OnParametersSetAsync: These methods are called whenever the component receives new parameter values. In server-side Blazor, since the app runs on the server, the parameters may be updated more frequently through user interactions, causing these methods to be called more often than in a client-side Blazor WebAssembly app.
  • OnAfterRender/OnAfterRenderAsync: These methods are called after every render, including the initial render. However, in a server-side Blazor app, since the component may be updated more frequently, these methods might be triggered more often than in a client-side Blazor WebAssembly app.
  • ShouldRender: This method is called before every re-render to determine if the component should update its DOM. In a server-side Blazor app, this method might be called more frequently due to the increased likelihood of state changes and updates.
  • Dispose: This method is called when the component is removed from the UI or when the application is terminated. In a server-side Blazor app, the component might be disposed more frequently due to differences in connection stability and life cycle.

In summary, the frequency and timing of some lifecycle events may differ between server-side Blazor and Blazor WebAssembly applications, primarily due to the different environments in which they are executed. The main difference is that server-side apps can experience more state changes and updates than client-side apps, which can cause some lifecycle events to be triggered more frequently.

How do you use the JSRuntime object to call JavaScript functions from your C# Blazor code, and what limitations and considerations must be made while doing so?


JSRuntime in Blazor enables you to call JavaScript functions from C# code. To use it, follow these steps:

  1. Inject the IJSRuntime service into your Blazor component using the @inject directive:
@inject IJSRuntime JSRuntime
  1. Use the InvokeAsync<T> method to call JavaScript functions. The method takes the name of the JavaScript function as its first argument, followed by any number of arguments that you need to pass to the JavaScript function:
private async Task CallJavaScriptFunction()
    await JSRuntime.InvokeVoidAsync("yourJavaScriptFunction", parameter1, parameter2);
  1. In your JavaScript file, define the function you want to call from C# code:
window.yourJavaScriptFunction = (parameter1, parameter2) => {
    // Your JavaScript code here.
  1. Include the JavaScript file in your application’s index.html (Blazor WebAssembly) or _Host.cshtml (Blazor Server) file.

When using the JSRuntime object, be aware of the following limitations and considerations:

  1. Async calls: JavaScript interop calls are asynchronous, which means you need to use async/await or Task to call JavaScript functions from C#.
  2. Error handling: JavaScript errors are propagated as JSException instances in C# code. Make sure to handle these exceptions to prevent unexpected behavior in your application.
  3. Marshalling data: Data types are marshalled between C# and JavaScript. While simple data types (numbers, strings, booleans) and arrays are usually compatible, you might need to serialize/deserialize more complex objects (e.g., using JSON).
  4. Performance impact: Frequent interop calls can have a performance impact on your application. Minimize the number of interop calls and batch multiple calls when possible.
  5. Security: Be cautious when executing JavaScript code from C#, as it can potentially introduce security vulnerabilities. Avoid running untrusted or user-generated JavaScript code.

By using JSRuntime, you can call JavaScript functions from your C# Blazor code, enabling you to perform tasks that are not natively supported by Blazor or that require direct interaction with the browser’s DOM or APIs.

Describe the use of middleware in a Blazor Server application, and what are the most common scenarios in which you would create custom middleware components?


Middleware in a Blazor Server application refers to the components that form the request pipeline. Middleware components receive incoming HTTP requests, process them in the order they appear in the pipeline, and generate responses. They have the ability to short-circuit the pipeline, preventing subsequent middleware components from being executed.

The most common scenarios in which you’d create custom middleware components are:

  1. Request/response logging: You might want to log the details of incoming requests and outgoing responses for debugging, auditing, or performance monitoring purposes.
  2. Authentication and authorization: You can create middleware to enforce authentication and authorization requirements. Middleware can check for the presence and validity of authentication tokens or inspect the user’s claims to determine if they have the required access.
  3. Caching: Middleware can be created to manage caching policies, store cached content, or serve cached responses for specific routes.
  4. Exception handling: A custom middleware component can centralize and unify error handling in your application. This can help maintain consistent error responses throughout the application.
  5. Rewriting URL paths: Middleware components can be used to rewrite URLs before they’re processed by the server, allowing your application to redirect, rewrite, or route requests dynamically.
  6. Rate limiting: If you want to limit the number of requests that your application can handle per user or time frame, custom middleware can enforce these rate limits.

To create custom middleware in a Blazor Server application, you can define a middleware component as a delegate or as a class with an Invoke or InvokeAsync method. Register the middleware in the Configure method of your Startup class by adding it to the IApplicationBuilder pipeline with the Use or UseMiddleware extension methods.

Now that we’ve got a solid grasp of using the JSRuntime object to call JavaScript functions from C# Blazor code, let’s shift our focus to another important aspect of Blazor development: middleware components.

Up next, we’ll discuss the use cases and implementation of custom middleware components in a Blazor Server application for better-request handling and more.

How can you use ILazyLoader to achieve component-level data lazy-loading in Blazor?


ILazyLoader is not a built-in interface or feature in Blazor. To achieve component-level data lazy-loading in Blazor, you can implement a custom asynchronous loading pattern using C# and Razor syntax, along with an interface to abstract the data-fetching logic. Here’s a brief overview of how to achieve component-level data lazy-loading in Blazor:

  1. Define an interface with a method for fetching the data (e.g., ILazyLoader.LoadDataAsync):
public interface ILazyLoader<TData>
    Task<TData> LoadDataAsync();
  1. Create a Blazor component that will use the ILazyLoader interface to fetch data asynchronously. Add a property for the ILazyLoader instance and a property to store the fetched data. Implement a loading pattern using the OnAfterRenderAsync lifecycle method.
@typeparam TData
@inject ILazyLoader<TData> LazyLoader
@implements IDisposable

<TData> FetchedData { get; set; }
bool IsLoaded { get; set; }

protected override async Task OnAfterRenderAsync(bool firstRender)
    if (firstRender && !IsLoaded)
        FetchedData = await LazyLoader.LoadDataAsync();
        IsLoaded = true;

public void Dispose()
    // Perform any cleanup tasks as required.
  1. Register your ILazyLoader<TData> implementation in the DI container, either in the Startup class or Program class.
services.AddScoped<ILazyLoader<YourDataModel>, YourLazyLoaderImplementation>();
  1. Use the lazy-loading component in your application to display data only when it’s fetched.

This approach uses an interface to abstract the data-fetching logic (ILazyLoader), a Blazor component that fetches data asynchronously when the component is rendered, and a loading pattern that ensures data is fetched only once.

What are the differences between state management in a Blazor Server application and a Blazor WebAssembly application, and how would you go about choosing the right approach for your project?


State management in Blazor Server and Blazor WebAssembly applications differ mainly in where the application’s state is maintained and how it is persisted.

In a Blazor Server application, the application state is maintained on the server for each active user session. This is because the components are executed on the server, and the generated UI updates are sent to the client via SignalR. This can cause the following implications for state management:

  • Scalability issues may arise as the application needs to track user sessions and maintain state for each connected user.
  • User session state can be lost if the server is restarted or crashes.

In a Blazor WebAssembly application, the application state is maintained on the client-side, as the components are executed directly in the user’s browser. This has the following implications for state management:

  • State is stored within the browser’s memory, so if the browser is closed or refreshed, the state can be lost.
  • Storing sensitive data in the client-side state can expose security risks, as an attacker could potentially access and manipulate this data.

When choosing the right state management approach for your project, consider the following factors:

  1. Type of application: If you expect your application to have a limited number of simultaneous users and require real-time connectivity to the server, a Blazor Server application might be more suitable. For a more scalable and responsive application, Blazor WebAssembly might be a better choice.
  2. Persistence requirements: If you need your application’s state to persist across different user sessions, consider using a state management solution that stores data either on the server or in more permanent client-side storage, such as LocalStorage or IndexedDB.
  3. Security: If you need to manage sensitive data, server-side state management might be preferred, as the data is stored on the server and less accessible to attackers. Client-side state management can still be used while taking precautions to store only non-sensitive data or encrypting sensitive data.
  4. Bandwidth and latency: Client-side state management can reduce bandwidth consumption and server load due to its local storage. However, server-side state management may help reduce latency when there’s a need for real-time communication with the server.

Ultimately, the choice between state management in a Blazor Server application and a Blazor WebAssembly application depends on your project’s goals, requirements, and constraints.

Describe the process of utilizing the Mediator pattern in a Blazor application and how it can facilitate better communication across different components.


The Mediator pattern is a behavioral design pattern that promotes loose coupling between components by having them communicate through a central mediator object rather than directly with each other. In a Blazor application, using the Mediator pattern can be beneficial for decoupling components, centralizing interactions, and facilitating easier communication.

Here’s a high-level overview of implementing the Mediator pattern in a Blazor application:

  1. Create a Mediator class to handle communication between components:
public class Mediator
    private Dictionary<string, Action<object>> _handlers = new();

    public void RegisterHandler(string key, Action<object> handler)
        _handlers[key] = handler;

    public void UnregisterHandler(string key)

    public void SendMessage(string key, object data)
        if (_handlers.TryGetValue(key, out var handler))
  1. Register the Mediator instance as a singleton service in your application’s dependency injection container:
  1. Have your components communicate through the Mediator by registering handlers and sending messages:
@inject Mediator Mediator
@implements IDisposable

private string _message;

protected override void OnInitialized()
    Mediator.RegisterHandler("MyComponentKey", HandleMessage);

private void HandleMessage(object data)
    _message = data.ToString();

public void Dispose()
  1. To send a message from one component to another, use the SendMessage method:
Mediator.SendMessage("MyComponentKey", "Hello, Component!");

By using the Mediator pattern in a Blazor application, you can create a central hub through which components communicate, reducing direct dependencies between components and making their interactions easier to manage and maintain.

How do you handle Blazor component disposal and what are the key considerations to ensure proper cleanup of resources, for both Blazor Server and WebAssembly applications?


Handling component disposal in Blazor involves releasing any resources allocated during the component’s lifecycle, such as unmanaged resources, timers, or event handlers. Properly disposing of these resources prevents memory leaks and ensures a clean shutdown.

To handle component disposal in Blazor, have your component implement the IDisposable interface:

@implements IDisposable

Then, override the Dispose method to release any resources your component has acquired:

public void Dispose()
    // Release your resources here, such as:
    // - Unsubscribe from event handlers
    // - Cancel timers or other recurring tasks
    // - Release unmanaged resources or objects implementing IDisposable

The key considerations to ensure proper resource cleanup in both Blazor Server and WebAssembly applications are:

  1. Consistently implement IDisposable: Ensure that components that acquire resources implement the IDisposable interface and properly release resources in the Dispose method.
  2. Dispose of composite resources: If your component has nested components that implement IDisposable, ensure to dispose of those components as well.
  3. Unsubscribing from event handlers: Unsubscribe from any event handlers your component subscribed to, even if they belong to other components. Otherwise, they might hold a reference to your component, preventing it from being garbage-collected.
  4. Canceling timers and recurring tasks: If your component uses timers or other recurring tasks (e.g., background threads or Task.Delay), ensure to cancel those tasks in the Dispose method to prevent them from running after the component has been destroyed.

By following these guidelines when disposing of Blazor components, you can help ensure proper cleanup of resources and prevent memory leaks in both Blazor Server and WebAssembly applications.

  1. When working with Blazor forms and validation, how can you create custom validation attributes and implement the IValidatableObject interface for complex validation logic?
    20.1. Answer:

Creating custom validation attributes in a Blazor application involves inheriting from the ValidationAttribute class and overriding the IsValid method. This method will contain the custom validation logic and will return a ValidationResult object based on whether the input value passes or fails the validation.

The IValidatableObject interface, on the other hand, provides a way to implement complex validation logic that cannot be achieved using validation attributes alone. By implementing the Validate method of this interface in your model class, you can add custom validation logic that involves multiple properties or requires knowledge of the entire model object’s state.

To use a custom validation attribute or implement IValidatableObject, follow these steps:

  1. Create a new class that inherits from ValidationAttribute and override the IsValid method for custom validation attribute or implement the IValidatableObject interface for complex validation logic.
public class CustomValidationAttribute : ValidationAttribute
    protected override ValidationResult IsValid(object value, ValidationContext validationContext)
        // Add custom validation logic here
        return new ValidationResult("Error message if validation fails");

public class MyModel : IValidatableObject
    public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
        // Add complex validation logic here
        yield return new ValidationResult("Error message if validation fails");
  1. In your Blazor component, import the custom validation using a using directive and apply the custom validation attribute to the desired property or implement IValidatableObject in your model class.
@using MyApp.ValidationAttributes

<EditForm Model="modelInstance" OnValidSubmit="HandleValidSubmit">
    <DataAnnotationsValidator />
    <ValidationSummary />

    <InputText @bind-Value="modelInstance.PropertyName" />
    <button type="submit">Submit</button>
  1. In the HandleValidSubmit method of your component, handle the form submission and handle any errors or validation results as needed.
private void HandleValidSubmit()
    // Handle successful form submission here

By following these steps, you can create custom validation attributes and implement complex validation logic with IValidatableObject in Blazor forms and validation.

We hope that this in-depth guide on Blazor interview questions and answers has equipped you with the knowledge and insights necessary to ace your upcoming interview. Remember, the key to conveying your expertise during the interview lies in providing clear and detailed explanations, along with practical examples wherever possible.

By mastering these Blazor interview questions and staying up-to-date with the latest developments in the Blazor ecosystem, you’ll be well-positioned to impress your interviewer and kickstart your career as a Blazor developer. Happy interviewing and all the best for your future endeavors!

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