JS repl

repl.js

const repl = "JS> ";

(function Repl() {
  let output;
  let reader = {
    onInputStreamReady : function(input) {
      var sin = Cc['@mozilla.org/scriptableinputstream;1']
                  .createInstance(Ci.nsIScriptableInputStream);
      sin.init(input);
      try {
        val = eval(sin.read(sin.available()));
        ret = val ? val.toString()+'\n' : "undefined\n";
        output.write(ret, ret.length);
      } catch (e) {
        output.write(e, e.length);
      }
      output.write(repl, repl.length);
      var tm = Cc["@mozilla.org/thread-manager;1"].getService();
      input.asyncWait(reader, 0, 0, tm.mainThread);
    }
  }
  let listener = {
    onSocketAccepted: function(serverSocket, clientSocket) {
      dump("Accepted connection on "+clientSocket.host + '\n');
      input = clientSocket.openInputStream(0, 0, 0)
                          .QueryInterface(Ci.nsIAsyncInputStream);
      output = clientSocket.openOutputStream(Ci.nsITransport.OPEN_BLOCKING, 0, 0);
      output.write(repl, repl.length);
      var tm = Cc["@mozilla.org/thread-manager;1"].getService();
      input.asyncWait(reader, 0, 0, tm.mainThread);
    }
  }
  var serverSocket = Cc['@mozilla.org/network/server-socket;1']
                       .createInstance(Ci.nsIServerSocket);
  serverSocket.init(31415, true, 5);
  dump("Opened socket on " + serverSocket.port + '\n');
  serverSocket.asyncListen(listener);
})();

Put into shell.js and |adb forward tcp:31415 tcp:31415|