How to remove the "Author" value and write a new author name

Hello,

I'm a dummy with scripting. I hope some experts can help me.

I'm working with FM11 and extendscript.

Now we have to insert metadata into the file info like "Author", "Title", "Keywords",....

As far I found the way to do it!

#target framemaker

var doc = app.ActiveDoc; 

var info = doc.PDFDocInfo;

var doctype = prompt("Possible cases: Installation manual, Operation manual, Installation and operation manual, Installer reference guide, User reference guide, Installer and user reference guide","Installation manual","Please input the type of manual");

info.push ("Author"); 

info.push (doctype); 

doc.PDFDocInfo = info;

Imagine that I run the script again, fill in a new entry in the inputbox, then the new entry does NOT overwrite the existing entry in the FM document.

Can somebody tell me (in dummy javascript language and step-by-step), how I can solve this issue for me?

Kind regards