Angular 2.0: What is the difference between a module's forRoot() and forChild() methods and why do we need it?

Answer 1

Call forRoot for root application module, AppModule. Calling it in any other module, particularly in a lazy loaded module

forRoot creates a module that contains all the directives, the given routes, and the router service itself.

Call forChild for child modules.

forChild creates a module that contains all the directives and the given routes, but does not include the router service.