@ngdoc overview
@name Forms
@description

Controls (`input`, `select`, `textarea`) are ways for a user to enter data.
A Form is a collection of controls for the purpose of grouping related controls together.

Form and controls provide validation services, so that the user can be notified of invalid input.
This provides a better user experience, because the user gets instant feedback on how to correct the error.
Keep in mind that while client-side validation plays an important role in providing good user experience, it can easily be circumvented and thus can not be trusted.
Server-side validation is still necessary for a secure application.


# Simple form
The key directive in understanding two-way data-binding is {@link ng.directive:ngModel ngModel}.
The `ngModel` directive provides the two-way data-binding by synchronizing the model to the view, as well as view to the model.
In addition it provides an {@link ngModel.NgModelController API} for other directives to augment its behavior.

<example>
  <file name="index.html">
    <div ng-controller="Controller">
      <form novalidate class="simple-form">
        Name: <input type="text" ng-model="user.name" /><br />
        E-mail: <input type="email" ng-model="user.email" /><br />
        Gender: <input type="radio" ng-model="user.gender" value="male" />male
        <input type="radio" ng-model="user.gender" value="female" />female<br />
        <button ng-click="reset()">RESET</button>
        <button ng-click="update(user)">SAVE</button>
      </form>
      <pre>form = {{user | json}}</pre>
      <pre>master = {{master | json}}</pre>
    </div>

    <script>
      function Controller($scope) {
        $scope.master = {};

        $scope.update = function(user) {
          $scope.master = angular.copy(user);
        };

        $scope.reset = function() {
          $scope.user = angular.copy($scope.master);
        };

        $scope.reset();
      }
    </script>
  </file>
</example>


Note that `novalidate` is used to disable browser's native form validation.



# Using CSS classes

To allow styling of form as well as controls, `ngModel`  adds these CSS classes:

- `ng-valid`
- `ng-invalid`
- `ng-pristine`
- `ng-dirty`

The following example uses the CSS to display validity of each form control.
In the example both `user.name` and `user.email` are required, but are rendered with red background only when they are dirty.
This ensures that the user is not distracted with an error until after interacting with the control, and failing to satisfy its validity.

<example>
  <file name="index.html">
    <div ng-controller="Controller">
      <form novalidate class="css-form">
        Name:
          <input type="text" ng-model="user.name" required /><br />
        E-mail: <input type="email" ng-model="user.email" required /><br />
        Gender: <input type="radio" ng-model="user.gender" value="male" />male
        <input type="radio" ng-model="user.gender" value="female" />female<br />
        <button ng-click="reset()">RESET</button>
        <button ng-click="update(user)">SAVE</button>
      </form>
    </div>

    <style type="text/css">
      .css-form input.ng-invalid.ng-dirty {
        background-color: #FA787E;
      }

      .css-form input.ng-valid.ng-dirty {
        background-color: #78FA89;
      }
    </style>

    <script>
      function Controller($scope) {
        $scope.master = {};

        $scope.update = function(user) {
          $scope.master = angular.copy(user);
        };

        $scope.reset = function() {
          $scope.user = angular.copy($scope.master);
        };

        $scope.reset();
      }
    </script>
  </file>
</example>



# Binding to form and control state

A form is an instance of {@link form.FormController FormController}.
The form instance can optionally be published into the scope using the `name` attribute.

Similarly, an input control that has the {@link ng.directive:ngModel ngModel} directive holds an
instance of {@link ngModel.NgModelController NgModelController}.
Such a control instance can be published as a property of the form instance using the `name` attribute
on the input control.  The name attribute specifies the name of the property on the form instance.

This implies that the internal state of both the form and the control is available for binding in
the view using the standard binding primitives.

This allows us to extend the above example with these features:

- RESET button is enabled only if form has some changes
- SAVE button is enabled only if form has some changes and is valid
- custom error messages for `user.email` and `user.agree`

<example>
  <file name="index.html">
    <div ng-controller="Controller">
      <form name="form" class="css-form" novalidate>
        Name:
          <input type="text" ng-model="user.name" name="uName" required /><br />
        E-mail:
          <input type="email" ng-model="user.email" name="uEmail" required/><br />
        <div ng-show="form.uEmail.$dirty && form.uEmail.$invalid">Invalid:
          <span ng-show="form.uEmail.$error.required">Tell us your email.</span>
          <span ng-show="form.uEmail.$error.email">This is not a valid email.</span>
        </div>

        Gender: <input type="radio" ng-model="user.gender" value="male" />male
        <input type="radio" ng-model="user.gender" value="female" />female<br />

        <input type="checkbox" ng-model="user.agree" name="userAgree" required />
        I agree: <input ng-show="user.agree" type="text" ng-model="user.agreeSign"
                  required /><br />
        <div ng-show="!user.agree || !user.agreeSign">Please agree and sign.</div>

        <button ng-click="reset()" ng-disabled="isUnchanged(user)">RESET</button>
        <button ng-click="update(user)"
                ng-disabled="form.$invalid || isUnchanged(user)">SAVE</button>
      </form>
    </div>
  </file>

  <file name="script.js">
    function Controller($scope) {
      $scope.master = {};

      $scope.update = function(user) {
        $scope.master = angular.copy(user);
      };

      $scope.reset = function() {
        $scope.user = angular.copy($scope.master);
      };

      $scope.isUnchanged = function(user) {
        return angular.equals(user, $scope.master);
      };

      $scope.reset();
    }
  </file>
</example>



# Custom triggers

By default, any change to the content will trigger a model update and form validation. You can
override this behavior using the {@link ng.directive:ngModelOptions ngModelOptions} directive to
bind only to specified list of events. I.e. `ng-model-options="{ updateOn: 'blur' }"` will update
and validate only after the control loses focus. You can set several events using a space delimited
list. I.e. `ng-model-options="{ updateOn: 'mousedown blur' }"`

If you want to keep the default behavior and just add new events that may trigger the model update
and validation, add "default" as one of the specified events.

I.e. `ng-model-options="{ updateOn: 'default blur' }"`

The following example shows how to override immediate updates. Changes on the inputs within the form will update the model 
only when the control loses focus (blur event).

<example>
  <file name="index.html">
    <div ng-controller="ControllerUpdateOn">
      <form>
        Name:
        <input type="text" ng-model="user.name" ng-model-options="{ updateOn: 'blur' }" /><br />
        Other data:
        <input type="text" ng-model="user.data" /><br />
      </form>
      <pre>username = "{{user.name}}"</pre>
    </div>
  </file>
  <file name="script.js">
    function ControllerUpdateOn($scope) {
      $scope.user = {};
    }
  </file>
</example>



# Non-immediate (debounced) model updates

You can delay the model update/validation by using the `debounce` key with the
{@link ng.directive:ngModelOptions ngModelOptions} directive. This delay will also apply to
parsers, validators and model flags like `$dirty` or `$pristine`.

I.e. `ng-model-options="{ debounce: 500 }"` will wait for half a second since
the last content change before triggering the model update and form validation.

If custom triggers are used, custom debouncing timeouts can be set for each event using an object
in `debounce`. This can be useful to force immediate updates on some specific circumstances
(like blur events).

I.e. `ng-model-options="{ updateOn: 'default blur', debounce: { default: 500, blur: 0 } }"`

If those attributes are added to an element, they will be applied to all the child elements and controls that inherit from it unless they are
overridden.

This example shows how to debounce model changes. Model will be updated only 250 milliseconds after last change.

<example>
  <file name="index.html">
    <div ng-controller="ControllerUpdateOn">
      <form>
        Name:
        <input type="text" ng-model="user.name" ng-model-options="{ debounce: 250 }" /><br />
      </form>
      <pre>username = "{{user.name}}"</pre>
    </div>
  </file>
  <file name="script.js">
    function ControllerUpdateOn($scope) {
      $scope.user = {};
    }
  </file>
</example>



# Custom Validation

Angular provides basic implementation for most common html5 {@link ng.directive:input input}
types: ({@link input[text] text}, {@link input[number] number}, {@link input[url] url}, {@link input[email] email}, {@link input[radio] radio}, {@link input[checkbox] checkbox}), as well as some directives for validation (`required`, `pattern`, `minlength`, `maxlength`, `min`, `max`).

Defining your own validator can be done by defining your own directive which adds a custom validation function to the `ngModel` {@link ngModel.NgModelController controller}.
To get a hold of the controller the directive specifies a dependency as shown in the example below.
The validation can occur in two places:

  * **Model to View update** -
    Whenever the bound model changes, all functions in {@link ngModel.NgModelController#properties_$formatters NgModelController#$formatters} array are pipe-lined, so that each of these functions has an opportunity to format the value and change validity state of the form control through {@link ngModel.NgModelController#$setValidity NgModelController#$setValidity}.

  * **View to Model update** -
    In a similar way, whenever a user interacts with a control it calls {@link ngModel.NgModelController#$setViewValue NgModelController#$setViewValue}.
This in turn pipelines all functions in the {@link ngModel.NgModelController#properties_$parsers NgModelController#$parsers} array, so that each of these functions has an opportunity to convert the value and change validity state of the form control through {@link ngModel.NgModelController#$setValidity NgModelController#$setValidity}.

In the following example we create two directives.

  * The first one is `integer` and it validates whether the input is a valid integer.
    For example `1.23` is an invalid value, since it contains a fraction.
    Note that we unshift the array instead of pushing.
    This is because we want to be first parser and consume the control string value, as we need to execute the validation function before a conversion to number occurs.

  * The second directive is a `smart-float`.
    It parses both `1.2` and `1,2` into a valid float number `1.2`.
    Note that we can't use input type `number` here as HTML5 browsers would not allow the user to type what it would consider an invalid number such as `1,2`.


<example module="form-example1">
  <file name="index.html">
    <form name="form" class="css-form" novalidate>
      <div>
        Size (integer 0 - 10):
        <input type="number" ng-model="size" name="size"
               min="0" max="10" integer />{{size}}<br />
        <span ng-show="form.size.$error.integer">This is not valid integer!</span>
        <span ng-show="form.size.$error.min || form.size.$error.max">
          The value must be in range 0 to 10!</span>
      </div>

      <div>
        Length (float):
        <input type="text" ng-model="length" name="length" smart-float />
        {{length}}<br />
        <span ng-show="form.length.$error.float">
          This is not a valid float number!</span>
      </div>
    </form>
  </file>

  <file name="script.js">
    var app = angular.module('form-example1', []);

    var INTEGER_REGEXP = /^\-?\d+$/;
    app.directive('integer', function() {
      return {
        require: 'ngModel',
        link: function(scope, elm, attrs, ctrl) {
          ctrl.$parsers.unshift(function(viewValue) {
            if (INTEGER_REGEXP.test(viewValue)) {
              // it is valid
              ctrl.$setValidity('integer', true);
              return viewValue;
            } else {
              // it is invalid, return undefined (no model update)
              ctrl.$setValidity('integer', false);
              return undefined;
            }
          });
        }
      };
    });

    var FLOAT_REGEXP = /^\-?\d+((\.|\,)\d+)?$/;
    app.directive('smartFloat', function() {
      return {
        require: 'ngModel',
        link: function(scope, elm, attrs, ctrl) {
          ctrl.$parsers.unshift(function(viewValue) {
            if (FLOAT_REGEXP.test(viewValue)) {
              ctrl.$setValidity('float', true);
              return parseFloat(viewValue.replace(',', '.'));
            } else {
              ctrl.$setValidity('float', false);
              return undefined;
            }
          });
        }
      };
    });
  </file>
</example>


# Implementing custom form controls (using `ngModel`)
Angular implements all of the basic HTML form controls ({@link ng.directive:input input}, {@link ng.directive:select select}, {@link ng.directive:textarea textarea}), which should be sufficient for most cases.
However, if you need more flexibility, you can write your own form control as a directive.

In order for custom control to work with `ngModel` and to achieve two-way data-binding it needs to:

  - implement `$render` method, which is responsible for rendering the data after it passed the {@link   api/ng.directive:ngModel.NgModelController#properties_$formatters NgModelController#$formatters},
  - call `$setViewValue` method, whenever the user interacts with the control and model needs to be updated. This is usually done inside a DOM Event listener.

See {@link guide/directive $compileProvider.directive} for more info.

The following example shows how to add two-way data-binding to contentEditable elements.

<example module="form-example2">
  <file name="index.html">
    <div contentEditable="true" ng-model="content" title="Click to edit">Some</div>
    <pre>model = {{content}}</pre>

    <style type="text/css">
      div[contentEditable] {
        cursor: pointer;
        background-color: #D0D0D0;
      }
    </style>
  </file>

  <file name="script.js">
    angular.module('form-example2', []).directive('contenteditable', function() {
      return {
        require: 'ngModel',
        link: function(scope, elm, attrs, ctrl) {
          // view -> model
          elm.on('blur', function() {
            scope.$apply(function() {
              ctrl.$setViewValue(elm.html());
            });
          });

          // model -> view
          ctrl.$render = function() {
            elm.html(ctrl.$viewValue);
          };

          // load init value from DOM
          ctrl.$setViewValue(elm.html());
        }
      };
    });
  </file>
</example>
