Assessing personalized directive attributes

I am currently working on a custom directive that will activate a specified event when a particular expression evaluates as true. The code below demonstrates how it can be achieved when binding a single value-

<div ng-trigger="value.someBoolean" /> 

app.directive('ngTrigger', [
    "$timeout","$log", function($timeout,$log) {
        return {
            restrict:"A",
            link: function(scope, elem, attr) {

                scope.$watch(attr.ngTrigger, function (e) {

                    if (e) {
                        $timeout(function() {
                            elem.triggerHandler('someevent');
                        });
                    } else {
                        $timeout(function () {
                            elem.triggerHandler('someotherevent');
                        });
                    }


                });

            }
        };

    }
]);

However, this method fails when binding a more complex expression like -

<div ng-trigger="!value.someBoolean && value.someOtherBoolean" />

I am seeking advice on how to modify this directive to handle complex expressions and ensure that it can detect changes in both parts of the expression simultaneously.

Answer №1

After some research and experimentation, I finally cracked the code. Referencing a helpful blog post on the $parse service was a game changer. This resource was instrumental in my breakthrough.

The key modification I made to my directive is as follows -

  app.directive('ngTrigger', [
    "$timeout","$parse","$log", function($timeout,$parse,$log) {
        return {
            restrict:"A",
            link: function(scope, elem, attr) {
                //create a model from the expression using parse
                var model = $parse(attr.ngTrigger);
                //watch the resulting model
                scope.$watch(model, function(val) {
                    if (val) {
                        $timeout(function () {
                            elem.triggerHandler(attr.ngTriggerTrue);
                        });
                    } else {
                        $timeout(function () {
                            elem.triggerHandler(attr.ngTriggerFalse);
                        });
                    }

                });

            }
        };

    }
]);

This technique works seamlessly with

<div ng-trigger="someValue.someBoolean"></div>

as well as

<div ng-trigger="someValue.someBoolean && someValue.someOtherBoolean"></div>

Answer №2

Have you considered using a watch with a functional approach instead of relying on a string expression? You could utilize scope.$eval like this:

scope.$watch(function(scope){return scope.$eval(attr.ngUpdate)}, function (e) {

Implementing this method is comparable to the parse method you previously mentioned.

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