AngularJS directive with default options

Question

I'm just starting with angularjs, and am working on converting a few old JQuery plugins to Angular directives. I'd like to define a set of default options for my (element) directive, which can be overridden by specifying the option value in an attribute.

I've had a look around for the way others have done this, and in the angular-ui library the ui.bootstrap.pagination seems to do something similar.

First all default options are defined in a constant object:

.constant('paginationConfig', {   itemsPerPage: 10,   boundaryLinks: false,   ... }) 

Then a getAttributeValue utility function is attached to the directive controller:

this.getAttributeValue = function(attribute, defaultValue, interpolate) {     return (angular.isDefined(attribute) ?             (interpolate ? $interpolate(attribute)($scope.$parent) :                            $scope.$parent.$eval(attribute)) : defaultValue); }; 

Finally, this is used in the linking function to read in attributes as

.directive('pagination', ['$parse', 'paginationConfig', function($parse, config) {     ...     controller: 'PaginationController',     link: function(scope, element, attrs, paginationCtrl) {         var boundaryLinks = paginationCtrl.getAttributeValue(attrs.boundaryLinks,  config.boundaryLinks);         var firstText = paginationCtrl.getAttributeValue(attrs.firstText, config.firstText, true);         ...     } }); 

This seems like a rather complicated setup for something as standard as wanting to replace a set of default values. Are there any other ways to do this that are common? Or is it normal to always define a utility function such as getAttributeValue and parse options in this way? I'm interested to find out what different strategies people have for this common task.

Also, as a bonus, I'm not clear why the interpolate parameter is required.

Answer 1

Use the =? flag for the property in the scope block of the directive.

angular.module('myApp',[])   .directive('myDirective', function(){     return {       template: 'hello {{name}}',       scope: {         // use the =? to denote the property as optional         name: '=?'       },       controller: function($scope){         // check if it was defined.  If not - set a default         $scope.name = angular.isDefined($scope.name) ? $scope.name : 'default name';       }     }   });