Understanding the Difference Between AOT and JIT in Angular

What is JIT Compilation?

Just-In-Time (JIT) Compilation is the default compilation mode used during development. In JIT, the Angular compiler compiles your app in the browser at runtime. This means that the compilation happens just before the app runs, and the code is compiled each time the app is loaded in the browser.

Advantages of JIT:

1. Faster Build Times: Since the compilation happens in the browser, the build process is typically faster during development.
2. Ease of Development: JIT allows for rapid prototyping and quicker iteration cycles because you don't have to wait for a full compile step.

Disadvantages of JIT:

1. Slower Initial Load Time: The app takes longer to load in the browser because the compilation happens at runtime.
2. Larger Bundle Size: JIT compiled code is larger because it includes the Angular compiler, which increases the size of the JavaScript bundles.

What is AOT Compilation?

Ahead-Of-Time (AOT) Compilation is a mode where the Angular compiler compiles your app at build time. The resulting JavaScript code is fully compiled and ready to be executed by the browser. This compilation happens once, during the build process, and the compiled code is served to the client.

Advantages of AOT:

1. Faster Initial Load Time: Since the compilation is done beforehand, the browser doesn't need to compile the code, resulting in a faster initial load.
2. Smaller Bundle Size: AOT compiled code is smaller because it doesn't include the Angular compiler.
3. Improved Security: AOT reduces the risk of injection attacks since the templates are pre-compiled and there's no template interpretation at runtime.

Disadvantages of AOT:

1. Slower Build Times: The build process can take longer because the compilation happens during the build step.
2. Complexity in Development: AOT may introduce some complexity and longer feedback cycles during development, especially when dealing with frequent changes.

When to Use JIT?

JIT is ideal during the development phase of your project. It provides faster build times and allows for quick iteration and testing. Use JIT when:

• You are in the early stages of development.
• You need rapid feedback and shorter development cycles.
• You want to quickly prototype and test new features.

When to Use AOT?

AOT is recommended for production builds. It ensures faster load times, smaller bundle sizes, and improved security. Use AOT when:

• You are ready to deploy your application to production.
• You want to optimize the performance and load times of your app.
• You are focused on minimizing the bundle size and improving security.

How to Use AOT and JIT in Angular?

To use JIT during development, you typically run:

ng serve

To use AOT for production builds, you run:

ng build --prod

This command ensures that your Angular app is compiled using AOT, providing the benefits of pre-compiled code.

Conclusion

Both AOT and JIT compilation have their own use cases and benefits. JIT is great for development due to its faster build times and ease of use, while AOT is essential for production to ensure better performance, smaller bundle sizes, and improved security. By understanding the differences and knowing when to use each, you can optimize your Angular development workflow and create efficient, high-performing applications.