Scope isolation prevents variables from being accessed in higher levels of the scope chain

Question

Scope isolation prevents variables from being accessed in higher levels of the scope chain

In my search for answers, I came across some similar questions on SO:

Isolate scope variable is undefined
unable to access rootscope var in directive scope

However, my question presents a unique scenario.

I am facing an issue with a directive that has an isolated scope. In the post link function of this directive, I am trying to access a variable that exists in the root (topmost) scope. Despite trying myVar: '@' and myVar: '=', I have been unsuccessful as the myVar remains undefined within the directive scope. Below is the return statement of my directive:

{
    restrict: 'E',
    replace: true,
    transclude: true,
    template: tmpl,

    scope: {
        myVar: '@'
    },

    link: {
        post: function ($scope) {
            // $scope.myVar is undefined
            // $scope.$root.myVar is defined
        }
    }
}

Upon inspecting the console, I observed that I can trace the $parent all the way up to the root and see that the variable is present there, accessible through the $root of the current scope.

So, my question arises - why do the '@' and '=' not work in this case? Could it be due to the variable being defined higher up in the hierarchy instead of the immediate parent, or perhaps because an isolated scope of a parent in between disrupts the reference chain to that variable?

javascript angularjs angularjs-directive angularjs-scope

Answer 1

Answer №1

When working with an isolated scope in a directive, it is important to pass the necessary values to the directive for it to utilize. For instance, consider the following example in our HTML:

 <my-example my-value='{{example}}'></my-example>

The main controller contains a scope variable called example:

var app = angular.module('exampleApp', []);

app.controller('MainCtrl', function($scope) {
  $scope.example = 'Hello';
});

In this case, the directive sets my-value equal to {{example}}.

As a result, the scope variable myValue in our directive will be linked to that value.

app.directive('myExample', function()  {
  return {
    restrict: 'E',
    replace: true,
    transclude: true,
    template: '<span>{{myValue}}</span>',

    scope: {
        myValue: '@'
    },

    link: {
        post: function (scope) {
            console.log(scope.myValue);
        }
    }
  }
});

For a demonstration of this concept, you can visit: http://plnkr.co/edit/rkbLJ0dJk4OrtyOD3c8w?p=preview

Answer 2

When working with an isolated scope in a directive, it is important to pass the necessary values to the directive for it to utilize. For instance, consider the following example in our HTML:

 <my-example my-value='{{example}}'></my-example>

The main controller contains a scope variable called example:

var app = angular.module('exampleApp', []);

app.controller('MainCtrl', function($scope) {
  $scope.example = 'Hello';
});

In this case, the directive sets my-value equal to {{example}}.

As a result, the scope variable myValue in our directive will be linked to that value.

app.directive('myExample', function()  {
  return {
    restrict: 'E',
    replace: true,
    transclude: true,
    template: '<span>{{myValue}}</span>',

    scope: {
        myValue: '@'
    },

    link: {
        post: function (scope) {
            console.log(scope.myValue);
        }
    }
  }
});

For a demonstration of this concept, you can visit: http://plnkr.co/edit/rkbLJ0dJk4OrtyOD3c8w?p=preview

Scope isolation prevents variables from being accessed in higher levels of the scope chain

Answer №1

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