Angular: A guide to binding to the required/ngRequired attribute

Question

Angular: A guide to binding to the required/ngRequired attribute

There is a directive that may or may not be required, and it can be used in two different ways.

<my-foo required></my-foo>

or

<my-foo ng-required="data.value > 10"></my-foo>

Even though require and ngRequire are essentially the same thing, you would expect the directive to work like this

HTML:

<my-foo ng-require="data.isRequired"></my-foo>

JS:

...
.directive('myFoo', function () {
    return {
    restrict: 'E',
    scope: {
       required: '='
    }
    ...

DEMO

However, this approach does not work as expected because scope.require is undefined. To resolve this issue, the scope definition needs to be modified to

scope: {
    required: '=ngRequired'
}

So, the question arises: what is the best way to handle both situations so that the value is stored in scope.required? Should both definitions be included or should attrs be used from the link function?

javascript angularjs angularjs-directive required

Answer 1

Answer №1

There are two main options you can consider:

1. Create a custom form element that supports `ng-model`

If you look into the source code of the ng-required directive, you will see that it specifically works with the ng-model controller:

restrict: 'A',
require: '?ngModel',
link: function(scope, elm, attr, ctrl) {
  if (!ctrl) return;
  attr.required = true; // ensure truthy value for non-input elements

  ctrl.$validators.required = function(modelValue, viewValue) {
    return !attr.required || !ctrl.$isEmpty(viewValue);
  };

  attr.$observe('required', function() {
    ctrl.$validate();
  });
}

So, if your custom directive already supports ng-model, then it automatically supports ng-required as well. For example:

angular.module('test', [])
.directive('myInput', function(){
  return {
    restrict: 'E',
    require: 'ngModel',
    scope: true,
    template: '<div><button ng-click="changeValue()">Change Value from: {{currentValue}}</button></div>',
    link: function (scope, element, attrs, ngModelCtrl) {
        ngModelCtrl.$parsers.push(function(val){
          if(!val){
            return null;
          }
          return parseFloat(val, 10) * 100;
        });
        ngModelCtrl.$render = function() {
           scope.currentValue = ngModelCtrl.$viewValue || 'No value';
        };
        scope.changeValue = function read(){
          var newValue = Math.random();
          if(newValue > 0.5){
            ngModelCtrl.$setViewValue(newValue + "");
          } else {
            ngModelCtrl.$setViewValue(null);
          }
          ngModelCtrl.$render();
        };
    }
  };
});

2. Modify an existing directive and include `ng-required`:

angular.module('test', [])
  .directive('myFormElement', function() {
      return {
        restrict: 'E',
        scope: {
          model: '=',
          required: '='
        },
        template: '<div>Enter number: <input type="number" ng-model="data.number" ng-required="required"></div>'
  };

  });

<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.23/angular.min.js"></script>


<div ng-app="test" ng-init="data={value:'Initial', required: false}">
  <form>
    Is required: <input type="checkbox" ng-model="data.required">
    <my-form-element required="data.required" model="data"></my-form-element>
  </form>
</div>

Answer 2

There are two main options you can consider:

1. Create a custom form element that supports `ng-model`

If you look into the source code of the ng-required directive, you will see that it specifically works with the ng-model controller:

restrict: 'A',
require: '?ngModel',
link: function(scope, elm, attr, ctrl) {
  if (!ctrl) return;
  attr.required = true; // ensure truthy value for non-input elements

  ctrl.$validators.required = function(modelValue, viewValue) {
    return !attr.required || !ctrl.$isEmpty(viewValue);
  };

  attr.$observe('required', function() {
    ctrl.$validate();
  });
}

So, if your custom directive already supports ng-model, then it automatically supports ng-required as well. For example:

angular.module('test', [])
.directive('myInput', function(){
  return {
    restrict: 'E',
    require: 'ngModel',
    scope: true,
    template: '<div><button ng-click="changeValue()">Change Value from: {{currentValue}}</button></div>',
    link: function (scope, element, attrs, ngModelCtrl) {
        ngModelCtrl.$parsers.push(function(val){
          if(!val){
            return null;
          }
          return parseFloat(val, 10) * 100;
        });
        ngModelCtrl.$render = function() {
           scope.currentValue = ngModelCtrl.$viewValue || 'No value';
        };
        scope.changeValue = function read(){
          var newValue = Math.random();
          if(newValue > 0.5){
            ngModelCtrl.$setViewValue(newValue + "");
          } else {
            ngModelCtrl.$setViewValue(null);
          }
          ngModelCtrl.$render();
        };
    }
  };
});

2. Modify an existing directive and include `ng-required`:

angular.module('test', [])
  .directive('myFormElement', function() {
      return {
        restrict: 'E',
        scope: {
          model: '=',
          required: '='
        },
        template: '<div>Enter number: <input type="number" ng-model="data.number" ng-required="required"></div>'
  };

  });

<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.23/angular.min.js"></script>


<div ng-app="test" ng-init="data={value:'Initial', required: false}">
  <form>
    Is required: <input type="checkbox" ng-model="data.required">
    <my-form-element required="data.required" model="data"></my-form-element>
  </form>
</div>

Angular: A guide to binding to the required/ngRequired attribute

Answer №1

1. Create a custom form element that supports `ng-model`

2. Modify an existing directive and include `ng-required`:

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Angular: A guide to binding to the required/ngRequired attribute

Answer №1

1. Create a custom form element that supports ng-model

2. Modify an existing directive and include ng-required:

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1. Create a custom form element that supports `ng-model`

2. Modify an existing directive and include `ng-required`: