useCategory.js

  addCategory: function(event) {
    event.preventDefault();
    var self = this;
    var useCategoryId = $('select[id=use_category_id]').val();

    this.model.set('category_id', parseInt(useCategoryId,10));
    this.model.save({ success: self.addedCategory });
  },

  addedCategory: function() {
    console.log('success');
  }