TabFS/extension/background.js

const ws = new WebSocket("ws://localhost:8888");

ws.onmessage = function(event) {
  const req = JSON.parse(event.data);

  let response;
  if (req.op === "readdir") {
    response = {
      op: "readdir",
      names: [".", "..", "hi.txt"]
    };
  }    

  ws.send(JSON.stringify(response));
};