node-tmp | Temporary file and directory creator for node.js | Runtime Evironment library

but closing the browser tab does NOT delete this file.

Closing a browser window does not normally give you any sort of server side notification that the browser window was closed.

There are various ways that developers work-around this:

1. Server-side session with session timeout. Create a server-side session object with a timeout and associate any created files with a particular session. When the session timeout expires because nobody who owns that session has visited the site in some period of time, then remove the files who's named are stored in that session.

2. WebSocket connection to monitor when connected. Use a webSocket connection from client to server to allow your server to monitor when the web page is still connected. Since the webSocket will be disconnected when the browser page is closed, you can use that event on the server to trigger the clearing of the files associated with that session. Note, that just navigating from one page to another within your site will also trigger the closing and then reopening of a webSocket so you will have to also use a timeout here. If a webSocket is closed by a user and then not reopened in some short period of time, you can assume the user has closed that browser window or navigated to some other site.

3. Hourly cleanup process. Use some sort of recurring cleanup process that ages away temp files based on the date/time they were created. Here, you could just run some function on a setInterval() every hour that checks for temp files that were created more than X hours ago and removes them.

let the tmp file be placed in localhost:3000/#/{FILE_ID}.txt

It's unclear exactly what you want here. http://localhost:3000/#/{FILE_ID}.txt is not a location in your file system. It's a URL that uses a hash location which won't even be passed directly to the server. In order to use that URL, you would have to have some client code that parsed the {FILE_ID}.txt and then did something with it (perhaps put it in an Ajax call).

Using Express, the way something like this would work is that you would have some sort of generic express request handler that would look at something in the URL and then would serve the appropriate temporary file. You can decide where you want to put the temporary files in your file system (that's entirely up to you). You just make sure that the code that puts the files there and the code that serves them up from a request uses the same location.

For example, one URL scheme you could use for the files is like this: