在Angular 2中，私有组件（未导出的组件）的用途是什么

Question

I understand that by exporting the components, a module can make them available to use in any modules those import it. But I am just wondering what would be the "useful" scenario where these components are not exported (or kept as private/local), but are just declared in it's parent module.

Answer 1

There's a methodology called lazy loading in Angular (as well as other forms of) development. The idea would be that each route, or family of routes would be their own module, with all of the components declared in the module. You would not export the components.

Instead where you configure your app routing, instead of passing a component for a route you would import the children of the Module you created for that route.

However some assets may need to be shared across the different routes. Maybe that would be a certain modal, or a navbar. Those components would be included in a module typically referred to as a SharedModule , and they would be exported from that module. The SharedModule would then be added as an import, and then your isolated modules you created for your routing would have access to those shared components (and likely pipes as well).

I hope that paints a decent picture as to how/why you would use modules, import modules, export components and what not. If you're interested in seeing what I mean you can take a dig through this codebase , specifically take a look at the file src/app/app-routing.module.ts for routing to modules, src/app/shared/shared.module.ts for exported components and what not, and maybe src/app/home/home.module.ts which will show you how I bring in the SharedModule but do not export anything from that module.