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Ahead-of-Time (AOT) Compiler - What Is the Angular Compiler?

What Is the Angular Compiler?
The Angular compiler converts our applications code (HTML and TypeScript) into JavaScript code before browser downloads and runs that code.

The @NgModule metadata plays an important role in guiding the compilation process and also tells the compiler what components to compile for this module and how to link this module with other modules.
The Angular offers two ways to compile our application code-
1.      Just-in-Time (JIT) - JIT compiles our app in the browser at runtime (compiles before running).
2.      Ahead-of-Time (AOT) - AOT compiles our app at build-time (compiles while running).

The JIT compilation is the default when we run the build or serve CLI commands -
ng build
ng serve


The AOT compilation, we append the --aot flags to build or serve CLI commands -
ng build --aot
ng serve --aot


Why we need Compilation in Angular?
We need compilation for achieving a higher level of efficiency, performance improvements, faster rendering and also sometimes detect template errors earlier in our Angular applications.

Why Compile with AOT?
1.      Faster Rendering
2.      Asynchronous Requests
3.      Detect template errors earlier
4.      Smaller Angular frameworks download size
5.      Better Security

What Is the difference between JIT compiler and AOT compiler?
JIT (Just-in-Time) -
1.      JIT compiles our app in the browser at runtime.
2.      Compiles before running
3.      Each file compiled separately
4.      No need to build after changing our app code and it automatically reflects the changes in your browser page
5.      Highly secure
6.      Very suitable for local development

AOT (Ahead-of-Time) -
1.      AOT compiles our app code at build time.
2.      Compiles while running
3.      Compiled by the machine itself, via the command line (Faster)
4.      All code compiled together, inlining HTML/CSS in the scripts
5.      Highly secure
6.      Very suitable for production builds

Angular Compiler Class –
class Compiler {
  // Compiles the given NgModule and all of its components
  compileModuleSync<T>(moduleType: Type<T>): NgModuleFactory<T>
 
  //Compiles the given NgModule and all of its components
  compileModuleAsync<T>(moduleType: Type<T>): Promise<NgModuleFactory<T>>

  //creates ComponentFactories for all components
  compileModuleAndAllComponentsSync<T>(moduleType: Type<T>): ModuleWithComponentFactories<T>

  ////creates ComponentFactories for all components
  compileModuleAndAllComponentsAsync<T>(moduleType: Type<T>): Promise<ModuleWithComponentFactories<T>>
 
  //Clears all caches.
  clearCache(): void

  //Clears the cache for the given component/ngModule.
  clearCacheFor(type: Type<any>)
}

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