Package contains one combined Angular compiler that provides:
- Typescript compilation
- Assets compilation (HTML, styles)
- Angular's AoT compilation
- Rollup's bundling with Tree Shaking
By default, this compiler compiles ts-files and component assets (HTML, LESS, and SASS) of an Angular app into CommonJS modules, which then are passed to Meteor to load. In this case, the app is bootstrapped using regular dynamic bootstrapping:
import {platformBrowserDynamic} from '@angular/platform-browser-dynamic';
import {AppModule} from './app.module';
platformBrowserDynamic().bootstrapModule(AppModule);In this case, Angular uses just-in-time template compiler to parse component templates before the app is loaded.
If the app is launched with the AOT environment variable preset, i.e, AOT=1 meteor,
the compiler's AoT mode comes into play. Compiler uses internally
Angular's CLI metadata and Angular's template compilers in order to
pre-compile component assets, first, into ES6 ts-modules, and then TypeScript compiler to
compile those ts-modules to regular ES6 js-modules. As a result,
each file with @Component, @Directive, or @NgModule annotations will
correspond internally to an ES6 js-module with the special Angular module component or module factories
(they usually have .ngfactory extension if processed with ngc directly).
On the final step all generated factory and component ES6 js-modules are bundled together using Rollup bundler in the Tree Shaking mode. Three Shaking is a special algorithm that traverses graph of the js-modules (mostly of NPMs but not only) to find modules that are imported but not used (or to be exact, exports of which are not used). Then, they are excluded from the bundle. For more info on that read here and here.
As you can see above, this mode introduces a couple of optimizations that take additional time to process making it a good fit for the production (more reasons you can find below) rather then for the development where you add new changes often and demand quick response from the compiler.
After the compilation, main Angular module factory should be bootstrapped as follows:
import {platformBrowser} from '@angular/platform-browser';
import {AppModuleNgFactory} from './app.module.ngfactory';
platformBrowser().bootstrapModuleFactory(AppModuleNgFactory);But the compiler takes care of you on this stage as well: you'll need only to add dynamic bootstrapping (as above), everything else is taken care of for you. Compiler will find most top Angular module of your app to boostrap and add bootstrapping code for you.
Main advantages of the additional processing:
- Components are loaded faster, hence app itself;
- Angular template compiler is not needed on the client side, hence the final js-bundle is smaller;
- Compiled code is considered more secure;
- You have chance to verify that templates are free of bugs, which is not fully available with the dynamic compilation;
- Tree Shaking reduces size of the final bundle.
For more info on the pluses and other details, please, read here.
TODO demo comes out as 1.4MB (not compressed) js-bundle in the default mode, at the same time it's of 1.1MB size in the AoT mode, which is 0.3MB less. It should be taken into account that for big apps difference can be even more substantial since more NPMs you use -- more chance that the number of unused exports will increase making Tree Shaking to unleash fully its power.
You can notice as well that the app starts off a bit faster, thanks to the pre-compiled assets.