WebIO + Interact + Mux does not work on pages other than "/"

[cstjean]

On the current #master, with Interact v0.10.3 and Mux v0.7.1, Interact widgets with Mux only work on /:

julia> using WebIO, Interact, Mux
   
julia> function gui()
           but = button("click me")
           on(but) do _
               println("was clicked")
           end
           but
       end
gui (generic function with 1 method)

julia> Mux.@app app = (Mux.defaults,
                       page("/", req->gui()),
                       page("/hallo", req->gui()),
                       Mux.notfound())

julia> webio_serve(app, 8000)
Task (runnable) @0x00007f359a5adae0

Then the button at http://localhost:8000 works, but not the one at http://localhost:8000/hallo

I believe that @stefan911 found the solution in #241 (comment) but I can't quite figure it out from his comment.

[etpinard]

Judging by

WebIO.jl/src/providers/mux.jl

Lines 20 to 29 in ee52ba2

	function webio_serve(app::Mux.App, args...)
	websock = Mux.App(Mux.mux(
	Mux.wdefaults,
	Mux.route("/webio-socket", create_socket),
	Mux.wclose,
	Mux.notfound(),
	))
	Mux.serve(app, websock, args...)
	end

the problem might be in

WebIO.jl/packages/mux-provider/src/mux.ts

Lines 9 to 16 in ee52ba2

	export const getMuxWSUrl = (): string => {
	const {protocol, host, pathname} = window.location;
	const wsProtocol = protocol == "https:" ? "wss:" : "ws:";
	const basePath = pathname[pathname.length - 1] == "/" ? pathname : pathname + "/";
	const wsPath = basePath + "webio-socket";
	return `${wsProtocol}//${host}${wsPath}`;
	};

which for http://localhost:8000/hallo returns ws://localhost:8000/hallo/webio-socket, but we need ws://localhost:8000/webio-socket/hallo for Mux.route("/webio-socket", create_socket) to pick up the request.

---

Before I make a PR, any info on the best way to test patches in the JS code would be much appreciated. Thanks!