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WebAssembly and Native AOT Compilation

Learn how WebAssembly and Native AOT enable high-performance applications at the edge and on servers.

By EMEPublished: February 20, 2025
webassemblywasmnative aotperformancecompilationblazordotnet

A Simple Analogy

Think of two runners preparing for a marathon:

  • WebAssembly is like pre-training at home—you practice running in different environments before the actual race. When you get to the browser, your code runs fast because it's already optimized.
  • Native AOT is like running with running shoes made just for you—instead of getting generic shoes at the race, you prepare them ahead of time. Your app starts instantly with no warm-up needed.

What Is WebAssembly (WASM)?

WebAssembly is a binary instruction format that runs in browsers and other environments. It allows you to run computationally intensive code at near-native speed in the browser—instead of just JavaScript.

Think of it as a universal translator: you can write code in C#, Rust, or C++, compile it to WebAssembly, and run it in any browser without JavaScript.

What Is Native AOT Compilation?

Native AOT (Ahead-Of-Time) is a compilation technique that converts .NET code directly to machine code before deployment. Instead of using Just-In-Time (JIT) compilation at runtime, Native AOT compiles everything upfront.

Why Use WebAssembly?

  • Performance: Run CPU-intensive computations in the browser (image processing, cryptography, math)
  • Reuse code: Share C# logic between server and browser
  • Offline capability: Complex features work without server
  • Language flexibility: Write in C#, Rust, or other languages, not just JavaScript

Why Use Native AOT?

  • Instant startup: No JIT compilation delay—code is ready immediately
  • Predictable performance: No garbage collection pauses or warm-up time
  • Smaller deployment: No runtime needed, just your compiled binary
  • Serverless-friendly: Perfect for AWS Lambda and Azure Functions
  • Security: Code is harder to decompile from a binary

WebAssembly in .NET: Blazor

Blazor WebAssembly

Run .NET in the browser with Blazor WebAssembly:

// C# running in the browser
@page "/calculator"
@code {
    int result = 0;

    void Add(int a, int b)
    {
        result = a + b;
    }
}

The C# compiles to WebAssembly, runs in the browser, and users interact with it directly—no server round-trip needed for calculations.

Setup

dotnet new blazorwasm -n MyBlazorApp
cd MyBlazorApp
dotnet run

Native AOT in .NET

Publish Your ASP.NET Core App as Native AOT

dotnet publish -c Release -r win-x64 --self-contained

This creates a standalone executable with no .NET runtime dependency.

Example: Lambda Function with Native AOT

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

app.MapGet("/hello", () => "Hello from Native AOT Lambda!");
app.Run();

Publish:

dotnet publish -c Release -r linux-x64 /p:PublishAot=true

Result: An ~50MB binary that starts instantly on AWS Lambda.

Practical Examples

WebAssembly Use Cases

  • Image editor: Load, resize, filter images in the browser without uploading
  • Encryption tool: Encrypt/decrypt files client-side for privacy
  • Game engine: Browser-based games with physics, collision detection
  • Data visualization: Real-time charts and complex calculations

Native AOT Use Cases

  • Microservices: Fast startup, lower memory (ideal for containerized deployments)
  • Serverless functions: Azure Functions and AWS Lambda with instant cold starts
  • CLI tools: Standalone executables with no runtime dependency
  • IoT: Deploy to edge devices with minimal resources

Real-World Scenarios

  • Stock trading app: WebAssembly for client-side calculations, Native AOT backend for fast order processing
  • Healthcare: WebAssembly for HIPAA-compliant client-side encryption, Native AOT for deployment in secure environments
  • EdTech: Blazor WebAssembly with math solver and coding IDE in browser
  • Enterprise: Native AOT microservices for rapid scaling in Kubernetes

Best Practices

WebAssembly:

  • Keep WASM binaries small (tree-trimming, lazy loading)
  • Use Interop carefully (calling JavaScript adds overhead)
  • Test performance in actual target browsers

Native AOT:

  • Use reflection sparingly (AOT needs to know types ahead of time)
  • Test extensively—some .NET features (serialization, reflection) need configuration
  • Monitor startup time improvements
  • Use Trim configuration for complex apps

Related Concepts to Explore

  • JIT vs. AOT compilation
  • Blazor Server (alternative to WebAssembly)
  • MSIL and IL (Intermediate Language)
  • Garbage collection and memory management
  • Containerization (Docker) for deployment
  • Edge computing and edge workers
  • Microservices architecture
  • WebAssembly System Interface (WASI)
  • Performance profiling and optimization
  • Cross-platform deployment strategies

Summary

WebAssembly and Native AOT represent two powerful optimization paths: WebAssembly brings high-performance computation to the browser, while Native AOT eliminates runtime overhead on servers and serverless platforms. Together, they enable developers to write once in C# and run everywhere—fast.