Blazor — Build Interactive Web UIs with C# Instead of JavaScript

Introduction

Blazor is a framework within ASP.NET Core that lets developers build interactive web UIs using C# instead of JavaScript. It supports both server-side rendering with real-time SignalR connections and client-side execution via WebAssembly, giving teams a single-language stack for full-stack web development.

What Blazor Does

• Renders interactive UI components written in C# and Razor syntax
• Runs client-side in the browser via WebAssembly (Blazor WASM) or server-side with SignalR (Blazor Server)
• Supports hybrid rendering modes mixing SSR, streaming, and interactivity per component
• Integrates with the full .NET ecosystem including EF Core, authentication, and dependency injection
• Enables code sharing between client and server with shared .NET libraries

Architecture Overview

Blazor uses a component model where each .razor file defines a reusable UI component with C# logic and HTML markup. In Server mode, UI events travel over a SignalR WebSocket to the server, which computes diffs and sends minimal DOM updates back. In WASM mode, the .NET runtime runs directly in the browser sandbox. .NET 8+ introduced unified rendering that lets each component choose its own render mode.

Self-Hosting & Configuration

• Install the .NET SDK (8.0+) from dotnet.microsoft.com
• Create a project with dotnet new blazor for the unified template
• Configure render modes in App.razor using @rendermode directives
• Deploy as a standard ASP.NET Core app behind Nginx, IIS, or in a container
• Publish WASM apps as static files to any CDN or static host

Key Features

• Full-stack C# eliminates the need for a separate JavaScript framework
• Component-based architecture with strong typing and IntelliSense
• Hot reload during development for rapid iteration
• Built-in form validation, authentication, and authorization
• AOT compilation for WebAssembly improves runtime performance

Comparison with Similar Tools

• React — JavaScript ecosystem with larger community; Blazor uses C# with smaller but growing ecosystem
• Angular — TypeScript-based with similar component model; Blazor integrates natively with .NET backend
• Svelte — Compiler-based approach with smaller bundles; Blazor WASM has larger initial download
• Leptos — Rust-based WASM framework; Blazor has broader enterprise adoption and tooling

FAQ

Q: Does Blazor replace JavaScript entirely? A: For most UI scenarios yes, but you can still call JavaScript via JS interop when needed for browser APIs or third-party JS libraries.

Q: How large is the Blazor WASM download? A: The initial download is around 2-5 MB for the .NET runtime, but subsequent loads are cached. AOT compilation and trimming can reduce this.

Q: Can Blazor be used for mobile apps? A: Yes, Blazor Hybrid with .NET MAUI lets you embed Blazor components in native iOS, Android, and desktop apps.

Q: Is Blazor production-ready? A: Yes, Blazor has been stable since .NET Core 3.1 and is used in production by many enterprises.

Sources

• https://github.com/dotnet/aspnetcore
• https://learn.microsoft.com/aspnet/core/blazor