I am trying to have the outlook meeting window pop up with pre-populated fields, upon the click of a button. The answers I have seen work for c# but I cant seem to make it work for js. For reference the answers are here
No, it is not. OfficeJS doesn't provide anything for that. Outlook web add-ins work under the context of currently selected item in Outlook. The best what you could do is to use EWS or Graph API for dealing with other items, but not displaying them in Outlook programmatically.