Shouldn't Angular 4 ReactiveFormsModule use forRoot pattern?

Question

I was reading through a really well written article about Angular's module loading here - https://medium.com/@cyrilletuzi/understanding-angular-modules-ngmodule-and-their-scopes-81e4ed6f7407

Since providers at feature modules' NgModule are actually injected globally (and eagerly), the article talks about the "forRoot" pattern used in modules like RouterModule.

I came across ReactiveFormsModule - https://angular.io/api/forms/ReactiveFormsModule - which has the FormBuilder provider, but it doesn't seem to use the forRoot pattern. Doesn't this mean every feature module using ReactiveFormsModule will end up re-creating the FormBuilder provider? Am I missing something?

read the article Avoiding common confusions with modules in Angular that expains the forRoot usage in depth — Max Koretskyi
– Max Koretskyi, Commented Oct 22, 2017 at 18:01

Günter Zöchbauer · Accepted Answer · 2017-10-22 16:34:35Z

4

forRoot is only relevant for lazy-loaded modules. For eager loaded modules, providers are registered in the application root scope anyway.

If you have imported ReactiveFormsModule in lazy loaded modules, then a FormBuilder instance per lazy-loaded module would be created. It doesn't really matter thought, because FormBuilder doesn't have a state. So not being singleton doesn't make a difference for how FormBuilder works and because it doesn't have a state, it also doesn't make a difference memory-wise.

answered Oct 22, 2017 at 16:34

Günter Zöchbauer

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2 Comments

raksugi Over a year ago

Makes sense. If I understood it right, adding forRoot to ReactiveFormsModule won't affect the behavior either. But for modules with services that have state, lazy loading can make a difference as injection happens at feature module level in that scenario. Pls correct me if I am wrong.

Günter Zöchbauer Over a year ago

It definitelly makes a difference if you want a single application-global service instance. Lazy loaded modules introduce a child-scope where they register their service providers, this results in a service instance per lazy loaded module instance and the service won't be available to non-lazy-loaded modules.

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