How to read an external file from elixir script (exs)?

I'm writing an exs file that renders liveview. Is it possible to read javascript from an external javascript file using a script tag like below ? I'm getting this error.

<script type="text/javascript" src="/assets/app.js"></script>

Error:
17:30:10.499 [error] #PID<0.385.0> running Example.Endpoint (connection #PID<0.383.0>, stream id 2) terminated
Server: localhost:5001 (http)
Request: GET /assets/app.js
** (exit) an exception was raised:
    ** (ArgumentError) unknown application: :sample
        (elixir 1.15.5) lib/application.ex:1010: Application.app_dir/1
        (plug 1.15.0) lib/plug/static.ex:420: Plug.Static.path/2
        (plug 1.15.0) lib/plug/static.ex:191: Plug.Static.call/2
        live.exs:108: Example.Endpoint.plug_builder_call/2
        live.exs:108: Example.Endpoint.call/2
        (plug_cowboy 2.6.1) lib/plug/cowboy/handler.ex:11: Plug.Cowboy.Handler.init/2

Here are my router and endpoint settings.

Application.put_env(:sample, Example.Endpoint,
  http: [ip: {127, 0, 0, 1}, port: 5001],
  server: true,
  live_view: [signing_salt: "aaaaaaaa"],
  secret_key_base: String.duplicate("a", 64)
)
defmodule Example.Router do
  use Phoenix.Router
  import Phoenix.LiveView.Router

  pipeline :browser do
    plug(:accepts, ["html"])
  end

  scope "/", Example do
    pipe_through(:browser)

    live("/", HomeLive, :index)
  end
end

defmodule Example.Endpoint do
  use Phoenix.Endpoint, otp_app: :sample
  socket("/live", Phoenix.LiveView.Socket)


  plug Plug.Static,
  at: "/",
  from: :sample,
  gzip: false,
  only: ~w(assets js fonts images uploads favicon.ico robots.txt)

  plug(Example.Router)
end

Solution

The Plug.Static docs describe how to reference a static file, specifically the :from option. From the docs, this value can be either:

a string containing a file system path
an atom representing the application name (where assets will be served from priv/static)
a tuple containing the application name and the directory to serve assets from (besides priv/static), or an MFA tuple.

Because you provided an atom (:sample), the resolution of the macro/function causes it to look for an app of that name in order to resolve its path to its priv/static directory.

Instead, you should double-quote the value so it is a string representing the path : "sample/path". I'm guessing the value represents a directory, but you'll have to play around with it to know for sure.