What classes should I add to module's declarations in Angular 4?

What classes should I add to module's declarations?
We can add the declarable classes like components, directives and pipes in the module's declarations list and we can add only - components, directives and pipes classes in the @NgModule.

Stayed Informed – Angular 4 Documentations with Example

What classes should I not add to module's declarations?

We do not declare - Module, Service, objects, strings, numbers, functions, entity models, configurations, business logic, and helper classes in the module's declarations.

Example –

export const sharedConfig: NgModule = {
    bootstrap: [ AppComponent ],
    declarations: [
        AppComponent,
        NavMenuComponent,
        HomeComponent,
        UserComponent,
        AccountDetailComponent,
        BarCodePipe
    ],
    imports: [
        RouterModule.forRoot([
            { path: '', redirectTo: 'home', pathMatch: 'full'},
            { path: 'home', component: HomeComponent },
            { path: 'user', component: UserComponent },
            { path: '**', redirectTo: 'home' }
        ])
    ],
    providers: [UserService]
};

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