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Forms

At the end of Managing Data, the online store application has a product catalog and a shopping cart.

In this section, you'll finish the app by adding a form-based checkout feature. You'll create a form to collect user information as part of checkout.

Forms in Angular

Forms in Angular take the standard capabilities of the HTML based forms and add an orchestration layer to help with creating custom form controls, and to supply great validation experiences. There are two parts to an Angular Reactive form, the objects that live in the component to store and manage the form, and the visualization of the form that lives in the template.

Define the checkout form model

First, you'll set up the checkout form model. The form model is the source of truth for the status of the form and is defined in the component class.

Open cart.component.ts.
Angular's FormBuilder service provides convenient methods for generating controls. As with the other services you've used, you need to import and inject the service before you can use it:
1. Import the FormBuilder service from the @angular/forms package.
The FormBuilder service is provided by the ReactiveFormsModule, which is already defined in the AppModule you modified previously (in app.module.ts).
1. Inject the FormBuilder service.
```
export class CartComponent {
  items;

  constructor(
    private cartService: CartService,
    private formBuilder: FormBuilder,
  ) { }
}
```
In the CartComponent class, define the checkoutForm property to store the form model.
```
export class CartComponent {
  items;
  checkoutForm;
}
```

During checkout, the app will prompt the user for a name and address. So that you can gather that information later, set the checkoutForm property with a form model containing name and address fields, using the FormBuilder#group() method.

export class CartComponent {
  items;
  checkoutForm;

  constructor(
    private formBuilder: FormBuilder,
    private cartService: CartService
  ) {
    this.items = this.cartService.getItems();

    this.checkoutForm = this.formBuilder.group({
      name: '',
      address: ''
    });
  }

For the checkout process, users need to be able to submit the form data (their name and address). When the order is submitted, the form should reset and the cart should clear.

In cart.component.ts, define an onSubmit() method to process the form. Use the CartService#clearCart() method to empty the cart items and reset the form after it is submitted. (In a real-world app, this method also would submit the data to an external server.)

The entire cart component is shown below:

The form model is defined in the component class. To reflect the model in the view, you'll need a checkout form.

Create the checkout form

Next, you'll add a checkout form at the bottom of the "Cart" page.

Open cart.component.html.
At the bottom of the template, add an empty HTML form to capture user information.
Use a formGroup property binding to bind the checkoutForm to the form tag in the template. Also include a "Purchase" button to submit the form.

<form [formGroup]="checkoutForm">

  <button class="button" type="submit">Purchase</button>  

</form>

<!-- 
  Note: The preview might contain an error message, which will be resolved by the following steps. 
  To do: Replace with docregion
  If you define the name and address fields here, it generates and error in the preview. 
  I had to add the formGroup property before the message would resolve. 
-->

On the form tag, use an ngSubmit event binding to listen for the form submission and call the onSubmit() method with the checkoutForm value.
```
<form [formGroup]="checkoutForm" (ngSubmit)="onSubmit(checkoutForm.value)">
...
</form>
```
Add input fields for name and address. Use the formControlName attribute binding to bind the checkoutForm form controls for name and address to their input fields. The final complete component is shown below:

After putting a few items in the cart, users can now review their items, enter name and address, and submit their purchase:

Next steps

Congratulations! You have a complete online store application with a product catalog, a shopping cart, and a checkout function.

Continue to the "Deployment" section to deploy your app to Firebase or move to local development.

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