By default, NgModules are eagerly loaded, which means that as soon as the app loads, so do all the NgModules, whether or not they are immediately necessary. For large apps with lots of routes, consider lazy loading—a design pattern that loads NgModules as needed. Lazy loading helps keep initial
bundle sizes smaller, which in turn helps decrease load times.
Navigate into the project by issuing the command `cd customer-app`.
## Create a feature module with routing
Next, you’ll need a feature module to route to. To make one, enter
the following command at the terminal window prompt where `customers` is the name of the module:
```sh
ng generate module customers --routing
```
This creates a customers folder with two files inside; `CustomersModule`
and `CustomersRoutingModule`. `CustomersModule` will act as the gatekeeper
for anything that concerns customers. `CustomersRoutingModule` will handle
any customer-related routing. This keeps the app’s structure organized as
the app grows and allows you to reuse this module while easily keeping its routing intact.
The CLI imports the `CustomersRoutingModule` into the `CustomersModule` by
adding a JavaScript import statement at the top of the file and adding
`CustomersRoutingModule` to the `@NgModule``imports` array.
## Add a component to the feature module
In order to see the module being lazy loaded in the browser, create a component to render some HTML when the app loads `CustomersModule`. At the command line, enter the following:
```sh
ng generate component customers/customer-list
```
This creates a folder inside of `customers` called `customer-list`
Each feature module acts as a doorway via the router. In the `AppRoutingModule`, you configure the routes to the feature modules, in this case `OrdersModule` and `CustomersModule`. This way, the router knows to go to the feature module. The feature module then connects the `AppRoutingModule` to the `CustomersRoutingModule` or the `OrdersRoutingModule`. Those routing modules tell the router where to go to load relevant components.
### Routes at the app level
In `AppRoutingModule`, update the `routes` array with the following:
The import statements stay the same. The first two paths are the routes to the `CustomersModule` and the `OrdersModule` respectively. Notice that the lazy loading syntax uses `loadChildren` followed by a function that uses the browser's built-in `import('...')` syntax for dynamic imports. The import path is the relative path to the module.
Next, take a look at `customers.module.ts`. If you’re using the CLI and following the steps outlined in this page, you don’t have to do anything here. The feature module is like a connector between the `AppRoutingModule` and the feature routing module. The `AppRoutingModule` imports the feature module, `CustomersModule`, and `CustomersModule` in turn imports the `CustomersRoutingModule`.
The `customers.module.ts` file imports the `CustomersRoutingModule` and `CustomerListComponent` so the `CustomersModule` class can have access to them. `CustomersRoutingModule` is then listed in the `@NgModule``imports` array giving `CustomersModule` access to its own routing module, and `CustomerListComponent` is in the `declarations` array, which means `CustomerListComponent` belongs to the `CustomersModule`.
### Configure the feature module’s routes
The next step is in `customers-routing.module.ts`. First, import the component at the top of the file with the other JavaScript import statements. Then, add the route to `CustomerListComponent`.
Notice that the `path` is set to an empty string. This is because the path in `AppRoutingModule` is already set to `customers`, so this route in the `CustomersRoutingModule`, is already within the `customers` context. Every route in this routing module is a child route.
Repeat this last step of importing the `OrdersListComponent` and configuring the Routes array for the `orders-routing.module.ts`:
You can check to see that a module is indeed being lazy loaded with the Chrome developer tools. In Chrome, open the dev tools by pressing `Cmd+Option+i` on a Mac or `Ctrl+Shift+j` on a PC and go to the Network Tab.
Click on the Orders or Customers button. If you see a chunk appear, you’ve wired everything up properly and the feature module is being lazy loaded. A chunk should appear for Orders and for Customers but will only appear once for each.
To see it again, or to test after working in the project, clear everything out by clicking the circle with a line through it in the upper left of the Network Tab:
Then reload with `Cmd+r` or `Ctrl+r`, depending on your platform.
## `forRoot()` and `forChild()`
You might have noticed that the CLI adds `RouterModule.forRoot(routes)` to the `app-routing.module.ts``imports` array. This lets Angular know that this module,
`AppRoutingModule`, is a routing module and `forRoot()` specifies that this is the root
routing module. It configures all the
routes you pass to it, gives you access to the router directives, and registers the `RouterService`.
Use `forRoot()` in the `AppRoutingModule`—that is, one time in the app at the root level.
The CLI also adds `RouterModule.forChild(routes)` to feature routing modules. This way, Angular
knows that the route list is only responsible for providing additional routes and is intended for feature modules. You can use `forChild()` in multiple modules.
`forRoot()` contains injector configuration which is global; such as configuring the Router. `forChild()` has no injector configuration, only directives such as `RouterOutlet` and `RouterLink`.
For more information, see the [`forRoot()` pattern](guide/singleton-services#forRoot) section of the [Singleton Services](guide/singleton-services) guide.
