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`:

Similar questions

How to send Multipart form data with a string payload

What is the method to determine the overall size of a webpage using the Google PageSpeed API?

When trying to use `slug.current` in the link href(`/product/${slug.current}`), it seems to be undefined. However, when I try to log it to the console, it is displaying correctly

Stop the Router from Displaying the Page momentarily prior to Redirecting

Storage in private Safari mode is not synced between tabs on mobile devices

How can I eliminate unwanted zombie events in Vue JS?

Utilizing JSON Data with JQuery: A Beginner's Guide

Utilizing a drop-down selection menu and a designated container to store chosen preferences

Preserving the table page number in Angular.js when updating a record in the application

What is the best way to position a popup div in CSS?

Issues with jQuery autocomplete functionality on certain elements are not uncommon

Access various data from the local storage and display them inside a div container

Differentiating between ng-show and ng-if in AngularJS

Error: Uncaught [🍍]: The function "getActivePinia()" was invoked without an active Pinia instance present. Ensure that you have called "app.use(pinia)" before attempting to utilize a store

Error occurred: Unable to access 'client' property as it is undefined. Process will continue running

Having trouble bypassing custom points on the reactive gauge speedometer

Recording a specialized event sent from a web component to React

How can I show the initial three digits and last three digits when using ngFor loop in Angular?

Is the attribute of the label malfunctioning within an Angular directive?

The map fails to load on the HTML page

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:

Similar questions

How to send Multipart form data with a string payload

What is the method to determine the overall size of a webpage using the Google PageSpeed API?

When trying to use `slug.current` in the link href(`/product/${slug.current}`), it seems to be undefined. However, when I try to log it to the console, it is displaying correctly

Stop the Router from Displaying the Page momentarily prior to Redirecting

Storage in private Safari mode is not synced between tabs on mobile devices

How can I eliminate unwanted zombie events in Vue JS?

Utilizing JSON Data with JQuery: A Beginner's Guide

Utilizing a drop-down selection menu and a designated container to store chosen preferences

Preserving the table page number in Angular.js when updating a record in the application

What is the best way to position a popup div in CSS?

Issues with jQuery autocomplete functionality on certain elements are not uncommon

Access various data from the local storage and display them inside a div container

Differentiating between ng-show and ng-if in AngularJS

Error: Uncaught [🍍]: The function "getActivePinia()" was invoked without an active Pinia instance present. Ensure that you have called "app.use(pinia)" before attempting to utilize a store

Error occurred: Unable to access 'client' property as it is undefined. Process will continue running

Having trouble bypassing custom points on the reactive gauge speedometer

Recording a specialized event sent from a web component to React

How can I show the initial three digits and last three digits when using ngFor loop in Angular?

Is the attribute of the label malfunctioning within an Angular directive?

The map fails to load on the HTML page

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

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