Angular custom form component / directive and $dirty property

When using regular input, such as

<form name="myForm">
  <input type="text" ng-model="foobar">
</form>

after typing in the input box myForm.$dirty is true.

I'd like to create a simple directive such as

angular.module('myModule', [])
.directive('myDirective', function() {
  return {
    restrict: 'E',
    scope: {
      fooBar: '='
    },
    template: '<div><button ng-click="fooBar=foo"></button><button ng-click="fooBar=bar"></button></div>'
  };
});

Sample usage would be

<form name="myForm">
  <my-directive foo-bar="myObj.foobarValue"></my-directive>
</form>

and after user clicks on any of the two buttons, myForm$dirty is set to true.

How is this accomplished?

Implementing custom form controls (using `ngModel`)

Use the ngModel controller and the object form of the require property in the DDO:

angular.module('myModule', [])
.directive('myDirective', function() {
  return {
    restrict: 'E',
    require: { ngModelCtrl: 'ngModel' },
    scope: {
      ngModel: '<'
    },
    bindToController: true,
    controllerAs: '$ctrl',
    template: 
       `<div>
          <button ng-click="$ctrl.ngModelCtrl.$setViewValue('foo')">
              Set foo
          </button>
          <button ng-click="$ctrl.ngModelCtrl.$setViewValue('bar')">
              Set bar
          </button>
       </div>`,
    controller: function ctrl() {}
  };
});

Usage:

<form name="myForm">
    <input type="text" ng-model="foobar">
    <my-directive ng-model="foobar"></my-directive>
</form>

By instantiating and using the ng-model controller, the directive will automatically set the form controls as necessary.

The DEMO

angular.module('myModule', [])
.directive('myDirective', function() {
  return {
    restrict: 'E',
    require: { ngModelCtrl: 'ngModel' },
    scope: {
      ngModel: '<'
    },
    bindToController: true,
    controllerAs: '$ctrl',
    template: 
       `<div>
          <button ng-click="$ctrl.ngModelCtrl.$setViewValue('foo')">
              Set foo
          </button>
          <button ng-click="$ctrl.ngModelCtrl.$setViewValue('bar')">
              Set bar
          </button>
       </div>`,
    controller: function ctrl() {}
  };
});

<script src="//unpkg.com/angular/angular.js"></script>
  <body ng-app="myModule">
    <h2>ngModel DEMO</h2>
    <form name="myForm">
        <input type="text" ng-model="foobar">
        <my-directive ng-model="foobar"></my-directive>
    </form>
    <br>myForm.$dirty = {{myForm.$dirty}}
    <br>myForm.$pristine = {{myForm.$pristine}}
    <br><button ng-click="myForm.$setDirty()">Set dirty</button>
    <br><button ng-click="myForm.$setPristine()">Set pristine</button>
  </body>

I recommend isolate scope with ngModel as an input. Output should be done with the $setViewValue method.

For more information, see