NgModule pitfalls

ngmodule.md

http://blog.angular-university.io/angular2-ngmodule/

Modules are very useful, but beware of the following pitfalls:

• do not redeclare a component, directive, etc. in more than one module
• modules do not create their own DI context, so injectables are available also outside the module
• unless the module is lazy loaded, in that case a separate DI context is created by the router to avoid accidental injectable overrides and prevent hard to troubleshoot bugs
• if you have a shared module that needs to be added to a lazy loaded module, make sure that it does not have providers, because that would create duplicate service instances (unless that is the intended behavior)

• providers: injectables (annotated by @Injectable()) available from this module's DI context (injector)
• declarations: components/directives/pipes included/defined in this module
• imports: modules depended by this module
• exports: components/directives/pipes exported by this module (these are visible to another module which imports this module)
• bootstrap: components for bootstrapping this module
• entryComponents: components that should be compiled
• schemas: ?