RouterModule.forRoot(ROUTES) vs RouterModule.forChild(ROUTES)

Question

What is the differences between these two and what are the use cases for each?

The docs aren\'t exactly helpful:

forRoot creates a module that con

Answer 1

Documentation clearly states what is the purpose of this distinction here: https://angular.io/docs/ts/latest/guide/ngmodule.html#!#core-for-root

Call forRoot only in the root application module, AppModule. Calling it in any other module, particularly in a lazy loaded module, is contrary to the intent and is likely to produce a runtime error.

Remember to import the result; don't add it to any other @NgModule list.

Every application has exactly one starting point (root) where the main routing service should be initialized with forRoot, while routes for particular "child" features should be registered additionaly with forChild. It is extremely useful for submodules and lazy loaded modules which do not have to be loaded at the application start, and as @Harry Ninh said they are told to reuse RouterService instead of registration of the new service, which may cause a runtime error.