Properties

The properties method is where you define the output of the items that goes into index you can query from the Query API

Properties example

properties: function (sourceEntity) {
  return {
      sku: sourceEntity.properties.sku, 
      title: sourceEntity.properties.title, 
      description: sourceEntity.properties.description,
      isActive: sourceEntity.properties.isActive
  };
}

The properties method must return an object with the values for the fields you defined in the index object.