Joplin server is available as a pre-release which Laurent has stated could be the starting point for a web application in the future - Joplin Server pre-release is now available but it doesn't offer what you are after at the moment.
You can also check out Foxmask's Joplin-Web but I have no idea what sort of level of functionality it offers at the moment.
The main Joplin app is also available as a portable application (on Windows) so if needed you can just load it all up onto a usb stick and use it wherever you want.
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