AOT vs. JIT in Angular

In Angular, AOT (Ahead-of-Time) and JIT (Just-in-Time) are two different compilation methods that determine how Angular applications are compiled and executed. Here’s a breakdown of their differences:

JIT (Just-in-Time) Compilation

• Definition: JIT compilation compiles the application in the browser at runtime.
• Process:
  • The Angular compiler is included in the application bundle.
  • The application is compiled when the browser loads it, meaning the compilation happens on-the-fly.
• Development Mode: JIT is typically used during development since it allows for quicker builds and easier debugging.
• Performance: Generally slower than AOT for production since the compilation happens in the browser, leading to longer load times.
• Error Detection: Errors can be caught during runtime, which might make debugging easier during development.
• Example: When you run ng serve in a development environment, Angular uses JIT compilation by default.

AOT (Ahead-of-Time) Compilation

• Definition: AOT compilation compiles the application at build time, before it is served to the browser.
• Process:
  • The Angular compiler processes the templates and components ahead of time and generates JavaScript code.
  • The application is compiled into a more optimized format, which is served to the browser.
• Production Mode: AOT is commonly used for production builds as it results in smaller bundle sizes and faster rendering.
• Performance: Generally faster than JIT since the compilation step is already completed before the application is loaded in the browser.
• Error Detection: Errors are caught during the build process, which can help in catching issues early.
• Example: When you run ng build --prod, Angular uses AOT compilation by default.

Key Differences

Feature	JIT (Just-in-Time)	AOT (Ahead-of-Time)
Compilation Time	At runtime in the browser	At build time, before serving to the browser
Performance	Slower, longer initial load times	Faster, optimized output for production
Bundle Size	Larger, includes the Angular compiler	Smaller, pre-compiled and optimized
Error Detection	Errors detected at runtime	Errors detected at build time
Use Case	Primarily for development	Primarily for production

Conclusion

• Use JIT for development to take advantage of faster builds and easier debugging.
• Use AOT for production to benefit from faster load times, smaller bundle sizes, and early error detection.

If you have more questions or need further clarification, feel free to ask!