As Marsha_R, there are any number of methods, properties, etc, in the Excel COM objects. There probably is a way to create a copy of a worksheet however, I'm not expert at using Excel COM (there may be others who are) so for me to come up with the JavaScript for you would mean I'd spend my work hours or personal time doing so.
So... what have you tried, if anything? The Excel COM objects are documented on Microsoft support forums so you may want to try googling your need and see if there is anything out there for you... what you are asking for is not a uniquely TestComplete thing since it's interacting with Excel... the same thing you could probably do in JavaScript via a web page or something.
Perhaps someone will post here what they've tried but it might be a good experience for you to see what's out there in forums more specifically dedicated to working with Excel via COM.
To prove my point, I took 5 minutes and found the following link by googling "copy sheet in workbook via COM". The code is in VB, but the concepts are the same and should be easily translatable to JavaScript.
https://msdn.microsoft.com/en-us/vba/excel-vba/articles/worksheet-copy-method-excel
