Ken Chatfield Ken Chatfield - 4 months ago 8
Javascript Question

Angular directive with default options

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.

OZ_ OZ_
Answer

You can use compile function - read attributes if they are not set - fill them with default value.

.directive('pagination', ['$parse', 'paginationConfig', function($parse, config) {
    ...
    controller: 'PaginationController',
    compile: function(element, attrs){
       if (!attrs.attrOne) { attrs.attrOne = 'default value'; }
       if (!attrs.attrTwo) { attrs.attrTwo = 42; }
    },
        ...
  }
});
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