google apps script - How to copy a file into a specific folder using DocsList?

Question

I am trying this code to copy a Google spreadsheet into a specific folder

var targetFolder = DocsList.createFolder("Testing");
var mainDocBlob = DocsList.getFileById("docId").getBlob();
var newMainDoc = targetFolder.createFile(mainDocBlob);

But the resulting file is a Pdf file instead of a spreadsheet as the source was.

How to do this right using DocsList and always getting the same type of file as the source is.

Thanks

Answer 1

The DriveApp Service was updated August 20, 2013, with new methods File.makeCopy(destination) and File.makeCopy(name, destination), which allow scripts to specify a folder to which a file should be copied.