Angular directive enabling two-way data binding

Question

Angular directive enabling two-way data binding

Feeling a bit lost with 2-way data binding in Angular. Take a look at this code snippet! the var bah can access the parent object $scope.something, but when I click the button, the value in the controller changes to false while it remains unchanged in the directive. What could be causing this? Is it a bug?

Any suggestions on how to solve this issue would be greatly appreciated. If possible, could you provide an example or reference links?

HTML

<div ng-controller="myController">
  show me something {{ something }} <br>
  <button ng-click="toggleSomething"><button>

  <!-- this is a canvas -->
  <my-directive></my-directive>
</div>

JS

angular.module('fooBar',[]).controller('myController', ['$scope', function($scope) {
   // this is the something
   $scope.something = true;

   $scope.toggleSomething = function(){
     if($scope.something) { 
       $scope.something = false 
     } else { 
       $scope.something = true 
     }
   }

}]).directive('myDirective', function(){
  return {
    template: '<canvas width="500px" height="500px"></canvas>',
    link: function(scope, el, attr) {
      //how to access that 'something'
      var bah = scope.$parent.something;
    }
  };
});

UPDATE Huge thanks to everyone, especially to @immirza for the assistance!

I apologize for not being able to respond individually. The solution was simply adding $parent.

//how to access that 'something'
var bah = scope.$parent.something

javascript angularjs angularjs-directive directive 2-way-object-databinding

Answer 1

Answer №1

To access the $scope.something directly in the myDirective, you don't need to use $parent because the directive has a shared scope.

If you want to detect changes in the something within the directive, simply calling console.log($scope.something) won't work as it is only executed once and won't print again after clicking. However, this doesn't mean that something hasn't changed inside the directive.

Additionally, there is an error in your ng-click where you have written ng-click="toggleSomething" instead of ng-click="toggleSomething()" since you are calling a function, not just a variable.

You can see a live demo here.

I included

<h1> ... {{ something }}</h1>

in the directive template to demonstrate that something works as expected inside the directive as well.

Check out this informative directive series for more insights.

Answer 2

To access the $scope.something directly in the myDirective, you don't need to use $parent because the directive has a shared scope.

If you want to detect changes in the something within the directive, simply calling console.log($scope.something) won't work as it is only executed once and won't print again after clicking. However, this doesn't mean that something hasn't changed inside the directive.

Additionally, there is an error in your ng-click where you have written ng-click="toggleSomething" instead of ng-click="toggleSomething()" since you are calling a function, not just a variable.

You can see a live demo here.

I included

<h1> ... {{ something }}</h1>

in the directive template to demonstrate that something works as expected inside the directive as well.

Check out this informative directive series for more insights.

Answer 3

Answer №2

I have set up a plunker using your code and implemented two-way binding in the directive. You can view it at plnkr

angular.module('fooBar',[]).controller('myctr', ['$scope', function($scope) {
   // this is the something
   $scope.something = true;

   $scope.toggleSomething = function(){
     if($scope.something) { 
       $scope.something = false 
     } else { 
       $scope.something = true 
     }
   }

}]).directive('myDirective', function(){
  return {
    //changed canvas to span for simplicity.
    template: '<span width="500px" height="500px">{{blah}} --- {{ dsomething }}</span>',
    scope: { dsomething: "=" },
    link: function(scope, el, attr) {

      //watching $parent.variable is not recommended as it makes your
      //directive less reusable and requires anyone who wants to use your
      //directive to create the variable.  dsomething will update
      //nicely without any code in this link function. the code below is just a demonstration
      //of how to do it using $watch with $parent scope.

      //how to access that 'something'
      if(!scope.dsomething){
        scope.dsomething = "something";
      }

      //because blah is a local variable and not a two-way binding variable,
      //we need to use $watch to update the value.
      //you can use "dsomething" instead of "$parent.something"
      //
      scope.$watch("$parent.something", function(newVal, oldVal){
         scope.blah = newVal;
      })
    }
  };
});

You can use your directive as:

<div ng-controller="myctr">
  show me something {{ something }}             <br />
  <button ng-click="toggleSomething()">Update Something</button>
  <button>
    <!-- this is a canvas -->
    <my-directive dsomething="something"></my-directive>
  </button>
</div>

Make sure to pay attention to the ng-click="toggleSomething()". It's a function call, not simply passing a function. Using ng-click="toggleSomething" alone won't work.

Answer 4

I have set up a plunker using your code and implemented two-way binding in the directive. You can view it at plnkr

angular.module('fooBar',[]).controller('myctr', ['$scope', function($scope) {
   // this is the something
   $scope.something = true;

   $scope.toggleSomething = function(){
     if($scope.something) { 
       $scope.something = false 
     } else { 
       $scope.something = true 
     }
   }

}]).directive('myDirective', function(){
  return {
    //changed canvas to span for simplicity.
    template: '<span width="500px" height="500px">{{blah}} --- {{ dsomething }}</span>',
    scope: { dsomething: "=" },
    link: function(scope, el, attr) {

      //watching $parent.variable is not recommended as it makes your
      //directive less reusable and requires anyone who wants to use your
      //directive to create the variable.  dsomething will update
      //nicely without any code in this link function. the code below is just a demonstration
      //of how to do it using $watch with $parent scope.

      //how to access that 'something'
      if(!scope.dsomething){
        scope.dsomething = "something";
      }

      //because blah is a local variable and not a two-way binding variable,
      //we need to use $watch to update the value.
      //you can use "dsomething" instead of "$parent.something"
      //
      scope.$watch("$parent.something", function(newVal, oldVal){
         scope.blah = newVal;
      })
    }
  };
});

You can use your directive as:

<div ng-controller="myctr">
  show me something {{ something }}             <br />
  <button ng-click="toggleSomething()">Update Something</button>
  <button>
    <!-- this is a canvas -->
    <my-directive dsomething="something"></my-directive>
  </button>
</div>

Make sure to pay attention to the ng-click="toggleSomething()". It's a function call, not simply passing a function. Using ng-click="toggleSomething" alone won't work.

Answer 5

Answer №3

There seems to be a misunderstanding regarding the concept of two-way data binding. Essentially, any element that is connected bidirectionally with a directive can be modified by either the controller or the directive, and the changes will automatically be reflected in the other.

By using $parent to retrieve the value in your directive, you are only accessing it without triggering a reevaluation of

var bah = scope.$parent.something

. This is because the value of scope.something has already been updated in the parent controller.

Answer 6

There seems to be a misunderstanding regarding the concept of two-way data binding. Essentially, any element that is connected bidirectionally with a directive can be modified by either the controller or the directive, and the changes will automatically be reflected in the other.

By using $parent to retrieve the value in your directive, you are only accessing it without triggering a reevaluation of

var bah = scope.$parent.something

. This is because the value of scope.something has already been updated in the parent controller.

Angular directive enabling two-way data binding

Answer №1

Answer №2

Answer №3

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