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How does Angular handle ahead-of-time (AOT) compilation?

Angular's Ahead-of-Time (AOT) compilation is a key feature that improves performance by compiling your Angular HTML and TypeScript code into efficient JavaScript code during the build process, before the browser downloads and runs it.

How does Angular handle ahead-of-time (AOT) compilation?

🔍 What AOT Compilation Does

When you build your Angular app with AOT:

  1. Template Compilation: Angular compiles HTML templates and components into JavaScript during build time.

  2. Type Checking: Errors in templates (e.g., wrong property binding) are caught early.

  3. Metadata Processing: Angular decorators (@Component, @NgModule, etc.) are processed and turned into actual code.

  4. Factory Generation: Angular generates "factory" classes that are used to create instances of components quickly at runtime.

🧠 How It Works (Simplified Flow)

  1. Build Step:

    • You run:

      ng build --aot

    • Angular compiler (ngc) processes your code and templates.

  2. Code Generation:

    • Instead of compiling templates at runtime (as in JIT), Angular pre-generates files like:

      my-component.ngfactory.js

  3. Optimized Output:

    • The output is smaller, faster, and safer, since the browser doesn’t need to do extra parsing or compilation.

✅ Advantages of AOT

BenefitDescription
🔥 Faster renderingTemplates are already compiled — browser does less work
🛡️ Fewer runtime errorsErrors caught at build time (e.g., typos in bindings)
🎯 Smaller bundlesTree-shaking removes unused code more effectively
🚀 Better securityNo dynamic template compilation = fewer XSS attack vectors

📦 Ivy & AOT (Post Angular 9)

With Angular Ivy (the new rendering engine from Angular 9+), AOT is:

  • Faster and more incremental (compiles only changed files)

  • On by default in production builds

🔧 Bonus Tip:

Always use AOT for production:

ng build --prod

This automatically enables AOT (and other optimizations like minification).

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