Does calling ko.mapping.fromJS two time is right thing to do?

Question

I am using knockout mapping plugin to map JSON data to knockout view model. The issue is JSON comes from server data doesn't have all the properties always. But my computed obeservables refer them. So I creates all the observable in first mapping using an empty object(templateStructure) contains all properties and then doing seocond call with actual data to populate the observable with current data. This works fine but want to know that if there any better way to handle the situation?

This is how the two time call is happening right now. templateStructure is dummay object with all the properties and data is actual data.

ko.mapping.fromJS(templateStructure, {}, this);
ko.mapping.fromJS(data, {}, this);

Answer 1

I have solved it using jQuery extend method by merging the object before mapping. So I only needed one call to the mapping function.

         var mergedData = jQuery.extend(true,data,templateStructure);
         ko.mapping.fromJS(mergedData, {}, this);