Where are all these files/extensions stored and Code

Hello! I have recently started creating a project on Xcode and I'm quite new and I've been coding other JavaScript previously. Here, I have heard about all these extensions/files such as root.plist and UserDefaults, etc, but I can't find them in the editor. I tried typing JavaScript code but it showed an error when I don't think there was. Is my app installed improperly or something? Please help, thanks!

Can you clarify what you have done till now on your Mac? In a usual app project of Xcode, you do not use JavaScript and there is no root.plist.

Where are all these files/extensions stored and Code
 
 
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