ngShow behaves unexpectedly when utilizing a personalized directive

In my Angular code, I have the following:

<span ng-mouseover="item.show_description=true" ng-mouseleave="item.show_description=false" pointer="{x: item.x, y: item.y}">
    {{item.label}}
</span>
<div class="description-popup" ng-show="!!item.description && item.show_description"
     style="left: {{item.x}}px; top: {{item.y}}px">
    <h2>{{item.label}}</h2>
    <p>{{item.description}}</p>
    <p>{{!!item.description && item.show_description}}</p>
</div>

The popup appears correctly, but even when the description is null or an empty string, the popup still shows up. In that case, the last expression shows false. Am I doing something wrong here? Or could it be a bug? I am using Angular 1.0.6 and cannot upgrade at the moment.

UPDATE:

I created a JSFiddle, and it seems like ng-show works as expected, except when I use the pointer directive that utilizes the mousemove event. The directive code is as follows:

app.directive('pointer', function($parse) {
    // Directive code omitted for clarity
});

Answer №1

The Significance of Isolate Scope

An issue arises with the use of ng-show when it inherits the scope of the directive it's placed on. If the directive has an isolate scope, then ng-show will only have access to that specific scope and not the outer scope.

In this scenario, it is likely that the directive description-popup utilizes an isolate scope, leading to limitations in accessing variables like item within the ng-show condition.

Understanding Isolate Scope

Isolate scope refers to a directive having its individual scope that does not derive from the surrounding scope. Unlike normal scopes, which inherit data from their surroundings, isolate scopes are independent entities without such inheritance.

Benefits of Implementing Isolate Scope

One primary advantage is reusability. By employing isolate scope, a directive can be reused across various contexts and scopes without concerns about variable conflicts between the directive's scope and the surrounding environment. Isolating the scope ensures independence, making it a favorable approach for directive design. The drawbacks are minimal, typically encountered when attempting to incorporate directives like ng-show or

ng-hide</code.</p>

<p><strong>Proposed Resolution</strong></p>

<p>To address this, consider placing your <code>ng-show
within an additional <div> encompassing the description-popup:

<div ng-show="!!item.description && item.show_description">
    <div class="description-popup"
         style="left: {{item.x}}px; top: {{item.y}}px">
        <h2>{{item.label}}</h2>
        <p>{{item.description}}</p>
        <p>{{!!item.description && item.show_description}}</p>
    </div>
</div>

This solution aligns with the desired behavior depicted in this JSFiddle.

Note that the information pertains mostly to versions of Angular prior to 1.2. Updates post-1.2 show improvements in how isolate scopes function: https://docs.angularjs.org/guide/migration#isolate-scope-only-exposed-to-directives-with-scope-property

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