The directive, which utilizes transcluded scope, is experiencing difficulties with two-way binding

Within my controller, there is a textbox linked to the model name. Inside this controller, there is a directive containing another textbox also bound to the model name:

<div class="border" ng-controller="editCtrl">
   Controller: editCtrl <br/>
   <input type="text" ng-model="name" />
   <br/>
   <tabs>
      Directive: tabs <br/>
      <input type="text" ng-model="name"/>
   </tabs>
</div>

mod.directive('tabs', function() {
  return {
    restrict: 'E',
    transclude: true, 
    template:
      '<div class="border" ng-transclude></div>',
  };
});

Typing in the outer textbox updates the inner textbox accordingly. However, typing in the inner textbox disconnects this synchronization ie. both textboxes no longer reflect the same value.

Example can be found at: http://jsfiddle.net/uzairfarooq/MNBLd/

I have attempted using two-way binding attributes (scope: {name: '='}), but it results in syntax errors. Additionally, utilizing scope: {name: '@'} yields the same outcome.

Any assistance on this matter would be greatly valued.

In alignment with the acknowledged solution, this informative article significantly contributed to my comprehension of prototypical inheritance within child scopes. I highly recommend anyone facing scope-related issues to delve into it comprehensively.

Answer №1

When a directive has transclude: true, it creates a new child scope that inherits prototypically from the parent scope, in this case, associated with the editCtrl controller.

Using two-way databinding in a child scope to bind to a parent scope property holding a primitive value, like name, can lead to unexpected behavior. Changes made in the child scope create a new property that overshadows the parent property's value. If the parent property is primitive, its value gets copied to the child property when created, affecting only the child's property on subsequent changes.

Prior to altering the second textbox, the child/transcluded scope accesses the parent scope's name property through inheritance. This explains why initially both textboxes are synchronized. Typing "Mark" into the first textbox results in:

To examine the scopes, I have provided a working example in this JSFiddle. By clicking the "show scope" link next to the second textbox before inputting any text, you can observe the transcluded child scope without a name property. Clear the console, type in the second textbox, then click the link again to see the added name property with the initial value inherited from the parent ("Mark"). Entering " likes Angular" shows:

The solutions are:

  1. Follow @pgreen2's advice and use an object instead of a primitive, ensuring no new properties are created in the child scope. E.g., define
    $scope.myObject = { name: "Mark", anotherProp: ... }
    within editCtrl's $scope.
  2. Incorporate $parent in the child scope by using ng-model="$parent.name", albeit this method is not recommended due to assumptions about HTML structure. The first picture demonstrates how this functions.

Errors arise with scope: {name: '='} due to restrictions on interpolation when employing two-way databinding (e.g., '=') - hence, {{}} cannot be used. Replace <tabs name="{{name}}"> with <tabs name="name">.

Using '@' mirrors the transclude scenario since ng-transclude utilizes the transcluded scope rather than the isolate scope established via scope: { ... }.

For further insights on scopes, including visual aids, refer to
What are the nuances of scope prototypal / prototypical inheritance in AngularJS?

Answer №2

It seems that the issue at hand is related to scoping. Initially, the inner textbox inherits the name from the outer scope since it is not set internally. This explains why changes made in the outer box reflect in the inner one. However, once modifications are made in the inner box, the internal scope now holds its own name, disconnecting it from the outer scope and causing the lack of synchronization.

The correct approach is to store models in the scope, rather than values directly. I have addressed this in my solution found here: http://jsfiddle.net/pdgreen/5RVza/. The key is to create a model object (data) and access values through it.

In the incorrect code, the directive modifies the scope, whereas in the corrected version, it only alters the model within the scope. This subtle distinction ensures proper scope inheritance.

I recall Miško Hevery's statement that in controllers, the scope should be treated as write-only, while in directives, it should be considered read-only.

Update: Watch the reference video for more insight: https://www.youtube.com/watch?v=ZhfUv0spHCY#t=29m19s

Answer №3

Syntax error occurs when a mistake is made in the writing of code, regardless of the framework or library being used. This could be due to missing commas or improperly closed parentheses. It's important to thoroughly review the code for any errors.

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