错误响应节点js API

I'm creating a node JS API (ES6) the app is using google firebase for auth db and more. I'm trying to sent the client a response back we there is an error like an invalid password I search a bit and I tried some things people say and no success.

EDIT:

I have edited the route so it will be like that now getting the error response but not with the response text i sent

in the route file I have:

app.route('/signin')
.post(auth.SignIn , function(req ,res) {
});

on the controller I have:

    exports.SignIn = function(req, res) {
  var email = req.body.email;
  var password = req.body.password;

  console.log(req.body.email + " - Attempting To SignIn");

  firebase.auth().signInWithEmailAndPassword(email, password).catch(function(error) {
    var errorCode = error.code;
    var errorMessage = error.message;
    console.log(errorCode + " - " + errorMessage);
    res.send(error.message);
  });

  console.log(email + " - Is Signed In - ");
}

on the client:

  $("#signinform").submit(function(event) {
    alert("test");
    /* stop form from submitting normally */
    event.preventDefault();
    var formData = {
      'email': $('input[name=ident]').val(),
      'password': $('input[type=password]').val()
    };


    $.ajax({
      type: 'POST',
      url: "http://localhost:3000/signin",
      data: formData,
      success: function(res){
        alert(res);
      },
      error: function(res){
        alert(res);
      }
    });

  });

when the log in is incorrect I get the error on the node.js console from this line:

console.log(errorCode + " - " + errorMessage);

if any one knows how to fix this I will be very happy :) Thanks.

Maybe you could fix it trying:

app.post('/signin',SignIn(req,res))