Angularjs controller function vs directive function - angularjs

Question

Lately I've been building some modules and in some of them I only used controllers (controller is set within an existing directive I already need to use to load template) to have this comunnication between services and the view, for example:
$scope.callFunction = function(data) {
factRequest = saveData(data);
};
I also noticed I could do this from within a directive, like this:
link:function(scope) {
scope.callFunction = function(data) {
factRequest.saveData(data);
}
}
//or..
link:function(scope, element, attr) {
attrValue = attr.myValue;
element.bind('click', function(attrValue) {
factRequest.saveData(attrValue);
});
}
//or even..
link:function(scope, element, attr) {
attrValue = attr.myValue;
element.bind('click', function(attrValue) {
factRequest.saveData(attrValue);
});
var elButton = element.fin('span'); //for example
elButton.bind('click', function(attrValue) {
factRequest.saveData(attrValue);
});
}
Considering a scenario where this a reusable object, for example, a product where it display on multiple pages and have a commom function, such as addFavorite, addCart, addWishList, etc.. And also considering performance.
What is the difference between those call methods? And what is the best option to use as a call Function?

Answer 1

To restate, you are calling a service method on a click event and want to know where the best place to put that logic is.
Let's look at each of your examples:
Controller
angular.module('myApp').controller('MyController', function($scope, factRequest) {
$scope.callFunction = function(data) {
factRequest.saveData(data);
};
});
First of all, whenever I find myself injecting $scope into a controller I question my approach. This is because adding variables to the current scope creates hidden dependencies if you are relying using those variables in a child controller -- and is unnecessary if you are not.
Instead, you should be using the controllerAs syntax and adding the function to the controller itself. Something like this:
angular.module('myApp').controller('MyController', function(factRequest) {
var vm = this;
vm.callFunction = function(data) {
factRequest.saveData(data);
};
});
...and you would access it in your template like this:
<div ng-controller="MyController as vm">
<input ng-model="vm.data">
<button ng-click="vm.callFunction(vm.data)">
Click Me!
</button>
</div>
This is a perfectly good approach utilizing native Angular directives.
Directive w/ Link Function
angular.module('myApp').directive('myDirective', function(factRequest) {
return {
link: function(scope) {
scope.callFunction = function(data) {
factRequest.saveData(data);
}
}
};
});
Again, I don't like this because you are adding the function to scope. If you have a directive and want to expose some functionality to the template, you should use a controller. For example:
angular.module('myApp').directive('myDirective', function() {
return {
controller: 'MyDirectiveController',
controllerAs: 'myDir',
template: '<input ng-model="myDir.data">' +
'<button ng-click="myDir.callFunction(myDir.data)">' +
'Click Me!' +
'</button>'
};
}).controller('MyDirectiveController', function(factRequest) {
var myDir = this;
myDir.callFunction = function(data) {
factRequest.saveData(data);
}
});
This is essentially the same as the first example, except that it is now a reusable component.
Directive w/ Click Event Handler
angular.module('myApp').directive('myDirective', function(factRequest) {
return {
link: function(scope, element, attr) {
element.on('click', function() {
factRequest.saveData(scope.$eval(attr.myValue));
});
}
};
});
Notice I took a few liberties here. For one thing, an event handler function gets the event object as its first argument, so trying to pass attr.myValue wouldn't work. Also, I call scope.$eval(), which is a best practice that enables the use of Angular expressions in the myValue attribute.
I like this approach best, because it doesn't rely on the use of other directives like ng-click. In other words, this directive is more self-contained.
One thing I should add is that Angular will not remove this event listener when the element is removed from the DOM. It is a best practice to clean up after your directive, like this:
angular.module('myApp').directive('myDirective', function(factRequest) {
return {
link: function(scope, element, attr) {
function onClick() {
factRequest.saveData(scope.$eval(attr.myValue));
}
element.on('click', onClick);
scope.$on('$destroy', function() {
element.off('click', onClick);
});
}
};
});
Conclusion
From a performance perspective, all of these approaches are roughly equivalent. The first two don't add any watchers themselves, but ng-click and ng-model do so its six of one, half a dozen of the other.