radio-track-by.js

function isDefinedAndNotNull(property) {
    return property !== undefined && property !== null;
};

angApp.directive("radioTrackBy", [function () {
    return {
        restrict: "A",
        scope: {
            ngModel: "=",
            ngValue: "=",
            radioTrackBy: "@"
        },
        link: function (ng, el, attrs) {
            // Set up the watch and reference it so we can remove it when we've got that initial piece of data
            var unWatch = ng.$watch(attrs.ngModel, function (newValue) {
                if (isDefinedAndNotNull(ng.ngModel) && isDefinedAndNotNull(ng.ngModel[ng.radioTrackBy])) {
                    // The model has been populated
                    if (ng.ngValue[ng.radioTrackBy] === ng.ngModel[ng.radioTrackBy]) {
			// The track-by property (from the radio's source list) and model property (currently selected radio button) match, set the model object to the matched object
                        ng.ngModel = ng.ngValue;
                    }
		    // We don't want to watch this anymore
                    unWatch();
                }
            });
        }
    };
}]);