*Reactive forms* provide a model-driven approach to handling form inputs whose values change over time. This guide shows you how to create and update a simple form control, progress to using multiple controls in a group, validate form values, and implement more advanced forms.
Reactive forms use an explicit and immutable approach to managing the state of a form at a given point in time. Each change to the form state returns a new state, which maintains the integrity of the model between changes. Reactive forms are built around observable streams, where form inputs and values are provided as streams of input values, which can be accessed synchronously.
Reactive forms also provide a straightforward path to testing because you are assured that your data is consistent and predictable when requested. Any consumers of the streams have access to manipulate that data safely.
Reactive forms differ from template-driven forms in distinct ways. Reactive forms provide more predictability with synchronous access to the data model, immutability with observable operators, and change tracking through observable streams. If you prefer direct access to modify data in your template, template-driven forms are less explicit because they rely on directives embedded in the template, along with mutable data to track changes asynchronously. See the [Forms Overview](guide/forms-overview) for detailed comparisons between the two paradigms.
This section describes how to add a single form control. In the example, the user enters their name into an input field, captures that input value, and displays the current value of the form control element.
The `FormControl` class is the basic building block when using reactive forms. To register a single form control, import the `FormControl` class into your component and create a new instance of the form control to save as a class property.
Use the constructor of `FormControl` to set its initial value, which in this case is an empty string. By creating these controls in your component class, you get immediate access to listen for, update, and validate the state of the form input.
After you create the control in the component class, you must associate it with a form control element in the template. Update the template with the form control using the `formControl` binding provided by `FormControlDirective` included in `ReactiveFormsModule`.
**Note:** For a more detailed list of classes and directives provided by `ReactiveFormsModule`, see the [Reactive forms API](#reactive-forms-api) section.
Using the template binding syntax, the form control is now registered to the `name` input element in the template. The form control and DOM element communicate with each other: the view reflects changes in the model, and the model reflects changes in the view.
the current state and value through the component class or the component template. The following examples display the value of the form control instance and change it.
* Through the `valueChanges` observable where you can listen for changes in the form's value in the template using `AsyncPipe` or in the component class using the `subscribe()` method.
* With the `value` property. which gives you a snapshot of the current value.
Reactive forms provide access to information about a given control through properties and methods provided with each instance. These properties and methods of the underlying [AbstractControl](api/forms/AbstractControl) class are used to control form state and determine when to display messages when handling validation. For more information, see [Simple form validation](#simple-form-validation) later in this guide.
Reactive forms have methods to change a control's value programmatically, which gives you the flexibility to update the value without user interaction. A form control instance provides a `setValue()` method that updates the value of the form control and validates the structure of the value provided against the control's structure. For example, when retrieving form data from a backend API or service, use the `setValue()` method to update the control to its new value, replacing the old value entirely.
Update the template with a button to simulate a name update. When you click the **Update Name** button, the value entered in the form control element is reflected as its current value.
The form model is the source of truth for the control, so when you click the button, the value of the input is changed within the component class, overriding its current value.
**Note:** In this example, you're using a single control. When using the `setValue()` method with a form group or form array instance, the value needs to match the structure of the group or array.
Just as a form control instance gives you control over a single input field, a form group instance tracks the form state of a group of form control instances (for example, a form). Each control in a form group instance is tracked by name when creating the form group. The following example shows how to manage multiple form control instances in a single group.
Create a property in the component class named `profileForm` and set the property to a new form group instance. To initialize the form group, provide the constructor with an object of named keys mapped to their control.
The individual form controls are now collected within a group. A `FormGroup` instance provides its model value as an object reduced from the values of each control in the group. A form group instance has the same properties (such as `value` and `untouched`) and methods (such as `setValue()`) as a form control instance.
A form group tracks the status and changes for each of its controls, so if one of the controls changes, the parent control also emits a new status or value change. The model for the group is maintained from its members. After you define the model, you must update the template to reflect the model in the view.
<code-examplepath="reactive-forms/src/app/profile-editor/profile-editor.component.1.html"region="formgroup"header="src/app/profile-editor/profile-editor.component.html (template form group)"></code-example>
Note that just as a form group contains a group of controls, the *profile form*`FormGroup` is bound to the `form` element with the `FormGroup` directive, creating a communication layer between the model and the form containing the inputs. The `formControlName` input provided by the `FormControlName` directive binds each individual input to the form control defined in `FormGroup`. The form controls communicate with their respective elements. They also communicate changes to the form group instance, which provides the source of truth for the model value.
The `ProfileEditor` component accepts input from the user, but in a real scenario you want to capture the form value and make available for further processing outside the component. The `FormGroup` directive listens for the `submit` event emitted by the `form` element and emits an `ngSubmit` event that you can bind to a callback function.
The `onSubmit()` method in the `ProfileEditor` component captures the current value of `profileForm`. Use `EventEmitter` to keep the form encapsulated and to provide the form value outside the component. The following example uses `console.warn` to log a message to the browser console.
The `submit` event is emitted by the `form` tag using the native DOM event. You trigger the event by clicking a button with `submit` type. This allows the user to press the **Enter** key to submit the completed form.
**Note:** The button in the snippet above also has a `disabled` binding attached to it to disable the button when `profileForm` is invalid. You aren't performing any validation yet, so the button is always enabled. Simple form validation is covered in the [Simple form validation](#simple-form-validation) section.
When building complex forms, managing the different areas of information is easier in smaller sections, and some groups of information naturally fall into the same group. Using a nested form group instance allows you to break large forms groups into smaller, more manageable ones.
An address is a good example of information that can be grouped together. Form groups can accept both form control and form group instances as children. This makes composing complex form models easier to maintain and logically group together. To create a nested group in `profileForm`, add a nested `address` element to the form group instance.
<code-examplepath="reactive-forms/src/app/profile-editor/profile-editor.component.1.ts"region="nested-formgroup"header="src/app/profile-editor/profile-editor.component.ts (nested form group)"></code-example>
In this example, `address group` combines the current `firstName` and `lastName` controls with the new `street`, `city`, `state`, and `zip` controls. Even though the `address` element in the form group is a child of the overall `profileForm` element in the form group, the same rules apply with value and status changes. Changes in status and value from the nested form group propagate to the parent form group, maintaining consistency with the overall model.
<code-examplepath="reactive-forms/src/app/profile-editor/profile-editor.component.1.html"region="formgroupname"header="src/app/profile-editor/profile-editor.component.html (template nested form group)"></code-example>
When updating the value for a form group instance that contains multiple controls, you may only want to update parts of the model. This section covers how to update specific parts of a form control data model.
* Use the `setValue()` method to set a new value for an individual control. The `setValue()` method strictly adheres to the structure of the form group and replaces the entire value for the control.
When a user clicks the button, the `profileForm` model is updated with new values for `firstName` and `street`. Notice that `street` is provided in an object inside the `address` property. This is necessary because the `patchValue()` method applies the update against the model structure. `PatchValue()` only updates properties that the form model defines.
Creating form control instances manually can become repetitive when dealing with multiple forms. The `FormBuilder` service provides convenient methods for generating controls.
The `FormBuilder` service is an injectable provider that is provided with the reactive forms module. Inject this dependency by adding it to the component constructor.
The `FormBuilder` service has three methods: `control()`, `group()`, and `array()`. These are factory methods for generating instances in your component classes including form controls, form groups, and form arrays.
In the example above, you use the `group()` method with the same object to define the properties in the model. The value for each control name is an array containing the initial value as the first item in the array.
**Note:** You can define the control with just the initial value, but if your controls need sync or async validation, add sync and async validators as the second and third items in the array.
_Form validation_ is used to validate user input to ensure it's complete and correct. This section covers adding a single validator to a form control and displaying the overall form status. Form validation is covered more extensively in the [Form Validation](guide/form-validation) guide.
Reactive forms include a set of validator functions for common use cases. These functions receive a control to validate against and return an error object or a null value based on the validation check.
HTML5 has a set of built-in attributes that you can use for native validation, including `required`, `minlength`, and `maxlength`. You can take advantage of these optional attributes on your form input elements. Add the `required` attribute to the `firstName` input element.
**Caution:** Use these HTML5 validation attributes *in combination with* the built-in validators provided by Angular's reactive forms. Using these in combination prevents errors when the expression is changed after the template has been checked.
When you add a required field to the form control, its initial status is invalid. This invalid status propagates to the parent form group element, making its status invalid. Access the current status of the form group instance through its `status` property.
The **Submit** button is disabled because `profileForm` is invalid due to the required `firstName` form control. After you fill out the `firstName` input, the form becomes valid and the **Submit** button is enabled.
`FormArray` is an alternative to `FormGroup` for managing any number of unnamed controls. As with form group instances, you can dynamically insert and remove controls from form array instances, and the form array instance value and validation status is calculated from its child controls. However, you don't need to define a key for each control by name, so this is a great option if you don't know the number of child values in advance. The following example shows you how to manage an array of *aliases* in `ProfileEditor`.
You can initialize a form array with any number of controls, from zero to many, by defining them in an array. Add an `aliases` property to the form group instance for `profileForm` to define the form array.
<code-examplepath="reactive-forms/src/app/profile-editor/profile-editor.component.ts"region="aliases"header="src/app/profile-editor/profile-editor.component.ts (aliases form array)">
A getter provides easy access to the aliases in the form array instance compared to repeating the `profileForm.get()` method to get each instance. The form array instance represents an undefined number of controls in an array. It's convenient to access a control through a getter, and this approach is easy to repeat for additional controls.
**Note:** Because the returned control is of the type `AbstractControl`, you need to provide an explicit type to access the method syntax for the form array instance.
Define a method to dynamically insert an alias control into the alias's form array. The `FormArray.push()` method inserts the control as a new item in the array.
To attach the aliases from your form model, you must add it to the template. Similar to the `formGroupName` input provided by `FormGroupNameDirective`, `formArrayName` binds communication from the form array instance to the template with `FormArrayNameDirective`.
<code-examplepath="reactive-forms/src/app/profile-editor/profile-editor.component.html"region="formarrayname"header="src/app/profile-editor/profile-editor.component.html (aliases form array template)"></code-example>
The `*ngFor` directive iterates over each form control instance provided by the aliases form array instance. Because form array elements are unnamed, you assign the index to the `i` variable and pass it to each control to bind it to the `formControlName` input.
Each time a new alias instance is added, the new form array instance is provided its control based on the index. This allows you to track each individual control when calculating the status and value of the root control.
Initially, the form contains one `Alias` field. To add another field, click the **Add Alias** button. You can also validate the array of aliases reported by the form model displayed by `Form Value` at the bottom of the template.
**Note:** Instead of a form control instance for each alias, you can compose another form group instance with additional fields. The process of defining a control for each item is the same.
The abstract base class for the concrete form control classes `FormControl`, `FormGroup`, and `FormArray`. It provides their common behaviors and properties.
Manages the value and validity state of a group of `AbstractControl` instances. The group's properties include its child controls. The top-level form in your component is `FormGroup`.
