carols10cents carols10cents - 3 months ago 26
AngularJS Question

How do I apply an AngularJS directive based on a class set by ng-class?

I'm trying to conditionally apply a directive to an element based on its class.

Here's a simple case of my issue, see the results in this fiddle. For this example, I'm using the map of class names to booleans form of

ng-class
with
true
; in my actual case I'd like to use the boolean result of a function.

Markup:

<div ng-app="example">
<div class="testcase">
This will have the directive applied as I expect
</div>
<div ng-class="{'testcase':true}">
This will not have the directive applied but I expect it to
</div>
</div>


JS:

angular.module('example', [])
.directive('testcase', function() {
return {
restrict: 'C',
link: function(scope, element, attrs) {
element.css('color', 'red');
}
}
}
);


Why isn't the directive being applied to the
div
that's getting its class through
ng-class
? Am I misunderstanding something about the order in which AngularJS is processing directives?

How should I be conditionally applying a directive to an element based on the evaluation of an expression?

Answer

ng-class just sets classes on the DOM, after the compilation process.

Perhaps a better way to apply the directive would be through an HTML attribute:

<div test-case>

Of course, this is not conditional, but I would leave the conditioning to the directive:

<div ng-app="example" ng-controller="exampleCtrl">
    <div test-case condition="dynamicCondition">Hello</div>
    <input type="checkbox" ng-model="dynamicCondition"/> Condition 
</div>

and

angular.module('example', [])
    .controller('exampleCtrl', function ($scope) {
        $scope.dynamicCondition = false;
    })
    .directive('testCase', function () {
    return {
        restrict: 'A',
        scope: {
            'condition': '='
        },
        link: function (scope, element, attrs) {
            scope.$watch('condition', function(condition){
                if(condition){
                    element.css('color', 'red');
                }
                else{
                    element.css('color', 'black');
                };
            });
        }
    }
});

Notice the directive name is testCaserather than testcase, the scope: {'condition': '='}, bit ensures that the condition attribute is synchronized and available as scope.condition and the watch evaluates the second argument every time the expression on the first changes value. JsFiddle over here.

Perhaps you should also look into ng-switch:

<div ng-switch="conditionFunction()">
  <div ng-when="true" test-case>Contents when conditionFunction() returns true</div>
  <div ng-when="false">Contents when conditionFunction() returns false</div>
</div>
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