Epress.js and AJAX, send JSON from server to client

I am trying to send JSON from Express.js back to client but I can't make it work.

routes/editor.js

exports.save = function(req, res){
    fs.readFile(__dirname + "/../public/index.html", function (err, data) {
        if (data == oldhash) {
          res.json({ r: 'no' })
        }
        else {
          res.json({ r: 'yes'})
        }
    });
});

public/javascript/test.js

$( ".save" ).click(function( event ) {
        event.preventDefault();

        $.ajax( {
          url: 'http://localhost:3000/save',
          data: r,
          type: 'GET',
          success: function(r) {
            if( r == 'yes' ) {
               $('#echoResult').append('<p>yes</p>');
            }
            else {
                $('#echoResult').append('<p>no</p>');
            }
          }
       });

    });

And then accordingly which is the response from the server, append the right HTML.

What am I missing here? All the AJAX examples I saw, they didn't help too much.

Any suggestions would be more than welcome.

Edit

I get this Error on client-> Uncaught ReferenceError: r is not defined

The client error can be resolved like this:

$( ".save" ).click(function( event ) {
    event.preventDefault();

    $.ajax( {
      url: 'http://localhost:3000/save',
      type: 'GET',
      success: function(data) {
        if( data.r == 'yes' ) {
           $('#echoResult').append('<p>yes</p>');
        }
        else {
            $('#echoResult').append('<p>no</p>');
        }
      }
   });

});

The data attribute is in the success callback with r as parameter.

Without more details about how you are using express I can't say much about the server code.