const CLIENT_READY = String.fromCharCode(0);
const CLIENT_KILL  = String.fromCharCode(1);
const CLIENT_PUSH  = String.fromCharCode(2);
const R_TYPES = {
	0: "fail", // the server could not start the subprocess
	1: "exit", // the subprocess exited
	2: "sout", // the process wrote new bytes to its standard output
	3: "serr"  // the process wrote new bytes to its standard error output
};

// Run the `/sh` command
let c = new WebSocket("ws://localhost:9001/sh");
c.onmessage = (e) => {
  let type = e.data.charCodeAt(0);
  let data = e.data.substring(1);
  if (type > 1) { // stdout has new bytes
    console.log(data); // print them to the console
  } else  {
    console.log("--- end of subprocess ---");
  }
}
c.send(CLIENT_READY);

// when you want to write something to to subprocess's stdin:
c.send(CLIENT_PUSH + "echo $USER\n");

// when you want to kill the subprocess
c.send(CLIENT_KILL);