Your other node would present the js file by way on an admin endpoint. Your other-other nodes would use a standard html script tag to import the JavaScript.
Any nodes' server-side js can generate an admin endpoint for resources to be consumed client side. In fact as of node-red 1.3.x you can just place files in a resources folder for it to be served up to the client. All you need then is the URL and you can consume the client side html script tag.
Note. This is all theory as I haven't tested it (but it works in my head - just haven't had a chance to try it out).
Ps, have a look at the js SRC for the serial node to see an example of an admin endpoint.
