Most effective communication strategy for directives

Originally sourced from here, but seeking more tailored responses here!

When dealing with nested directives, the need for communication between them arises. For example, inner directives may need to inform the outer directive about certain user choices.

<outer>
  <inner></inner>
  <inner></inner>
</outer>

Here are five approaches I've identified so far:

Using 'require' in conjunction with parent directive

The inner directive can require the outer directive and access a method exposed by its controller. In the definition of the inner directive:

require: '^outer',
link: function(scope, iElement, iAttrs, outerController) {
   // This method can be invoked in the template using ng-click
   $scope.chosen = function() {
     outerController.chosen(something);
   }
}

The outer directive’s controller would look something like this:

controller: function($scope) {
   this.chosen = function(something) {
   }
}

Utilizing $emit events

The inner directive can use $emit to trigger an event that the outer directive responds to with $on. Within the inner directive's controller:

controller: function($scope) {
  $scope.chosen = function() {
    $scope.$emit('inner::chosen', something);
  }
}

And within the outer directive's controller:

controller: function($scope) {
  $scope.$on('inner::chosen, function(e, data) {
  }
}

Execution of expression in parent scope via &

An item can bind to an expression in the parent scope and execute it when appropriate. The HTML structure might look like this:

<outer>
  <inner inner-choose="functionOnOuter(item)"></inner>
  <inner inner-choose="functionOnOuter(item)"></inner>
</outer>

In the inner controller, there would be an 'innerChoose' function that could be called:

scope: {
  'innerChoose': '&'
},
controller: function() {
  $scope.click = function() {
    $scope.innerChoose({item:something});
  }
}

This would then trigger the 'functionOnOuter' function on the outer directive's scope:

controller: function($scope) {
  $scope.functionOnOuter = function(item) {
  }
}

Scope inheritance on non-isolated scopes

Since these are nested controllers, scope inheritance allows the inner directive to call functions in the scope chain (as long as it doesn’t have an isolated scope). In the inner directive:

// scope: anything but a hash {}
controller: function() {
  $scope.click = function() {
    $scope.functionOnOuter(something);
  }
}

And in the outer directive:

controller: function($scope) {
  $scope.functionOnOuter = function(item) {
  }
}

By injecting a service into both inner and outer directives

A shared service can be injected into both directives, allowing them direct access to the same object or the ability to notify the service of actions. They could even register themselves for notifications in a pub/sub system, without the need for nesting.

Question: What are the potential advantages and drawbacks of each approach compared to the others?

Answer №1

Initially, it is important to note a flaw in the example provided

<outer>
  <inner inner-choose="functionOnOuter(item)"></inner>
  <inner inner-choose="functionOnOuter(item)"></inner>
</outer>

This setup will not function properly with

scope: {
  'innerChoose': '&'
},
controller: function() {
  $scope.click = function() {
    $scope.innerChoose({item:something});
  }
}

To address this issue, you either must utilize $parse for the entire innerChoose expression or simply pass a reference to the function, as shown below:

<outer>
  <inner inner-choose="functionOnOuter"></inner>
  <inner inner-choose="functionOnOuter"></inner>
</outer>

The decision on which approach to take should be based on the stylistic preferences of your team and the specific requirements at hand. For instance, if you need to execute commands dynamically defined in JSON data that may vary in structure, utilizing events might be more suitable to ensure flexibility.

However, if your main objective is to build Views that make use of certain functionalities, employing a shared $scope could simplify the View creation process.

Personally, I mainly utilize require for ngModel, as it serves as a sibling directive rather than a parent directive. So far, I have not encountered a scenario where referencing the entire parent controller was necessary.

Answer №2

When faced with a hierarchy like this, my preference is to opt for the initial choice. The use of require was specifically designed to tightly connect two directives or components in Angular 1.5. This highlights the fact that you cannot utilize inner independently of outer.

I tend to steer clear of events as they can traverse multiple scopes if not utilized correctly.

& and scope settings offer certain benefits, but their applicability varies depending on your specific requirements. They are not a one-size-fits-all solution.

In today's discussions, it's important to consider Angular 2. In this version, if you need to run a function from a child component, you must pass this component using the @ViewChild annotation. In Angular 1.x, the closest alternative would be to leverage require, which serves a similar purpose for components in this version as well.

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