docs: update and improve docs for input, ngModelController, and guide/forms

docs/content/guide/forms.ngdoc

@@ -7,15 +7,17 @@ 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.
+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.
+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 module="formExample">
   <file name="index.html">
@@ -60,16 +62,20 @@ Note that `novalidate` is used to disable browser's native form validation.
 
 To allow styling of form as well as controls, `ngModel`  adds these CSS classes:
 
-- `ng-valid`
-- `ng-invalid`
-- `ng-pristine`
-- `ng-dirty`
-- `ng-touched`
-- `ng-untouched`
+- `ng-valid`: the model is valid
+- `ng-invalid`: the model is invalid
+- `ng-valid-[key]`: for each valid key added by `$setValidity`
+- `ng-invalid-[key]`: for each invalid key added by `$setValidity`
+- `ng-pristine`: the control hasn't been interacted with yet
+- `ng-dirty`: the control has been interacted with
+- `ng-touched`: the control has been blurred
+- `ng-untouched`: the control hasn't been blurred
+- `ng-pending`: any `$asyncValidators` are unfulfilled
 
 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.
+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 module="formExample">
   <file name="index.html">
@@ -122,9 +128,9 @@ 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.
+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.
@@ -187,7 +193,7 @@ This allows us to extend the above example with these features:
 
 
 
-# Custom triggers
+# Custom model update 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
@@ -200,8 +206,8 @@ 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).
+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 module="customTriggerExample">
   <file name="index.html">
@@ -241,10 +247,11 @@ in `debounce`. This can be useful to force immediate updates on some specific ci
 
 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.
+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.
+This example shows how to debounce model changes. Model will be updated only 250 milliseconds
+after last change.
 
 <example module="debounceExample">
   <file name="index.html">
@@ -264,39 +271,40 @@ This example shows how to debounce model changes. Model will be updated only 250
   </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`).
-
-You can define your own validator by defining a directive which adds a validation function to the `ngModel` {@link ngModel.NgModelController controller}.
-The directive can get ahold of `ngModel` by specifying `require: 'ngModel'` in the directive definition.
-See below for an example.
-
-Validation runs in two places:
-
-  * **Model to View update** -
-    The functions in {@link ngModel.NgModelController#$formatters `NgModelController.$formatters`} are pipelined.
-    Whenever the bound model changes, 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 runs all functions in the {@link ngModel.NgModelController#$parsers `NgModelController.$parsers`} array as a pipeline. Each function in `$parsers` has an opportunity to convert the value and change validity state of the form control through {@link ngModel.NgModelController#$setValidity `NgModelController.$setValidity`}.
-
-In the following example we create two directives.
-
-  * The first one is `integer` and it validates whether the input is a valid integer.
-    For example `1.23` is an invalid value, since it contains a fraction.
-    Note that we unshift the array instead of pushing.
-    This is because we want it to be the first parser and consume the control string value, as we need to execute the validation function before a conversion to number occurs.
-
-  * The second directive is a `smart-float`.
-    It parses both `1.2` and `1,2` into a valid float number `1.2`.
-    Note that we can't use input type `number` here as HTML5 browsers would not allow the user to type what it would consider an invalid number such as `1,2`.
-
+types: ({@link input[text] text}, {@link input[number] number}, {@link input[url] url},
+{@link input[email] email}, {@link input[radio] radio}, {@link input[checkbox] checkbox}),
+as well as some directives for validation (`required`, `pattern`, `minlength`, `maxlength`,
+`min`, `max`).
+
+With a custom directive, you can add your own validation functions to the `$validators` object on
+the {@link ngModel.NgModelController `ngModelController`}. To get a hold of the controller,
+you require it in the directive as shown in the example below.
+
+Each function in the `$validators` object receives the `modelValue` and the `viewValue`
+as parameters. Angular will then call `$setValidity` internally with the function's return value
+(`true`: valid, `false`: invalid). The validation functions are executed every time an input
+is changed (`$setViewValue` is called) or whenever the bound `model` changes.
+Validation happens after successfully running `$parsers` and `$formatters`, respectively.
+Failed validators are stored by key in
+{@link ngModel.NgModelController#$error `ngModelController.$error`}.
+
+Additionally, there is the `$asyncValidators` object which handles asynchronous validation,
+such as making an `$http` request to the backend. Functions added to the object must return
+a promise that must be `resolved` when valid or `rejected` when invalid.
+In-progress async validations are stored by key in
+{@link ngModel.NgModelController#$pending `ngModelController.$pending`}.
+
+In the following example we create two directives:
+ * An `integer` directive that validates whether the input is a valid integer. For example,
+ `1.23` is an invalid value, since it contains a fraction. Note that we validate the viewValue
+ (the string value of the control), and not the modelValue. This is because input[number] converts
+ the viewValue to a number when running the `$parsers`.
+
+ * A `username` directive that asynchronously checks if a user-entered value is already taken.
+ We mock the server request with a `$q` deferred.
 
 <example module="form-example1">
   <file name="index.html">
@@ -305,18 +313,18 @@ In the following example we create two directives.
         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.integer">The value is not a 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.$error.float">
-          This is not a valid float number!</span>
+        Username:
+        <input type="text" ng-model="name" name="name" username />{{name}}<br />
+        <span ng-show="form.name.$pending.username">Checking if this name is available ...</span>
+        <span ng-show="form.name.$error.username">This username is already taken!</span>
       </div>
+
     </form>
   </file>
 
@@ -328,35 +336,96 @@ In the following example we create two directives.
       return {
         require: 'ngModel',
         link: function(scope, elm, attrs, ctrl) {
-          ctrl.$parsers.unshift(function(viewValue) {
+          ctrl.$validators.integer = function(modelValue, viewValue) {
+            if (ctrl.$isEmpty(modelValue)) {
+              // consider empty models to be valid
+              return true;
+            }
+
             if (INTEGER_REGEXP.test(viewValue)) {
               // it is valid
-              ctrl.$setValidity('integer', true);
-              return viewValue;
-            } else {
-              // it is invalid, return undefined (no model update)
-              ctrl.$setValidity('integer', false);
-              return undefined;
+              return true;
             }
-          });
+
+            // it is invalid
+            return false;
+          };
         }
       };
     });
 
-    var FLOAT_REGEXP = /^\-?\d+((\.|\,)\d+)?$/;
-    app.directive('smartFloat', function() {
+    app.directive('username', function($q, $timeout) {
       return {
         require: 'ngModel',
         link: function(scope, elm, attrs, ctrl) {
-          ctrl.$parsers.unshift(function(viewValue) {
-            if (FLOAT_REGEXP.test(viewValue)) {
-              ctrl.$setValidity('float', true);
-              return parseFloat(viewValue.replace(',', '.'));
-            } else {
-              ctrl.$setValidity('float', false);
-              return undefined;
+        var usernames = ['Jim', 'John', 'Jill', 'Jackie'];
+
+          ctrl.$asyncValidators.username = function(modelValue, viewValue) {
+
+            if (ctrl.$isEmpty(modelValue)) {
+              // consider empty model valid
+              return $q.when();
             }
-          });
+
+            var def = $q.defer();
+
+            $timeout(function() {
+              // Mock a delayed response
+              if (usernames.indexOf(modelValue) === -1) {
+                // The username is available
+                def.resolve();
+              } else {
+                def.reject();
+              }
+
+            }, 2000);
+
+            return def.promise;
+          };
+        }
+      };
+    });
+  </file>
+</example>
+
+# Modifying built-in validators
+
+Since Angular itself uses `$validators`, you can easily replace or remove built-in validators,
+should you find it necessary. The following example shows you how to overwrite the email validator
+in `input[email]` from a custom directive so that it requires a specific top-level domain,
+`example.com` to be present.
+Note that you can alternatively use `ng-pattern` to further restrict the validation.
+
+<example module="form-example-modify-validators">
+  <file name="index.html">
+    <form name="form" class="css-form" novalidate>
+      <div>
+        Overwritten Email:
+        <input type="email" ng-model="myEmail" overwrite-email name="overwrittenEmail" />
+        <span ng-show="form.overwrittenEmail.$error.email">This email format is invalid!</span><br>
+        Model: {{myEmail}}
+        </div>
+    </form>
+  </file>
+
+  <file name="script.js">
+    var app = angular.module('form-example-modify-validators', []);
+
+    app.directive('overwriteEmail', function() {
+      var EMAIL_REGEXP = /^[a-z0-9!#$%&'*+/=?^_`{|}~.-]+@example\.com$/i;
+
+      return {
+        require: 'ngModel',
+        restrict: '',
+        link: function(scope, elm, attrs, ctrl) {
+          // only apply the validator if ngModel is present and Angular has added the email validator
+          if (ctrl && ctrl.$validators.email) {
+
+            // this will overwrite the default Angular email validator
+            ctrl.$validators.email = function(modelValue) {
+              return ctrl.$isEmpty(modelValue) || EMAIL_REGEXP.test(modelValue);
+            };
+          }
         }
       };
     });
@@ -365,13 +434,17 @@ In the following example we create two directives.
 
 
 # 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.
+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 `$render` method, which is responsible for rendering the data after it passed the {@link ngModel.NgModelController#$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.
+  - implement `$render` method, which is responsible for rendering the data after it passed the
+  {@link ngModel.NgModelController#$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.