A JavaScript application could be anything that loads in a webpage but not necessarily from a server or domain. That could mean pasted into the console as you suggested, a SharePoint utility, any web page that does not sending data to the server, as well as pages opened from the local file system.

The primary considerations for success are high portability, data saved in the browser’s localStorage, applications that execute in the browser as opposed to on a server, no dependencies, and high performance.