using promise for ajax calls

gistfile1.js

var Foods = {
	category: function(cats_url){
		var promise = $.Deferred();
		$.ajax(cats_url, {
      	success: function(dat) {
					promise.resolve(dat); 
				}
				error: function(){
  				var error = 'invalid food';
  				promise.reject(error);
				}
		});
    return promise;
  }
}

var foodPromise = Foods.category(cats_url);
foodPromise.done(function(result) {
	foodThing.category_foods(result)
}


$.when(
     Foods.category(cats_url),
     Foods.category(units_by_food_url)
).then(function(catsResult, unitsResult){
     foodThing.category_foods(catsResult)
     foodThing.food.units(unitsResult);
}