奇怪的问题Highchart滴答间隔

Question

I don't know whether I am doing something wrong or this is strange issue in Highcharts, Actually I am interested to change x and y axis tickmark using input box, if its possible to update tickmark interval without redraw its well and good,

Here strange issue is following has no effect onchange

     var dummy = $('#xint').val(); 
     chart.xAxis[0].options.tickInterval = dummy ;

but if I define variable dummy like this, tick intervals are getting updated, I really don't know whats really wrong here.. please some one help me

Here is link to Fiddle

      var dummy = 0.2;
      chart.xAxis[0].options.tickInterval = dummy ;

HTML

    <script src="http://code.highcharts.com/highcharts.js"></script>
    <div id="container" style="height: 400px"></div>

    <input id='xint' type='number'>

JAVASCRIPT

     $(function () {
var chart = new Highcharts.Chart({
    chart: {
        renderTo: 'container',
        zoomType: 'xy',
        marginLeft: 50,
        marginBottom: 90
    },

    yAxis: {
        reversed: true,
        //min: 0,
        //max: 50
    },
    plotOptions: {
        series: {
            stacking: 'normal'
        }
    },
    xAxis: {
        opposite: true  
    },
    series: [{
        name: '01-Jan-2014',
        data: [
            [28, 10],
            [30, 0]
        ]
    }]
});

$('#xint').change(function(){

        setTimeout(function() { alert($('#xint').val());},10);

        // This is not working 
       // var dummy = $('#xint').val();

       // where as this is working..
         var dummy = 0.2;

             chart.xAxis[0].options.tickInterval = dummy ;
             chart.xAxis[0].isDirty = true;
             chart.redraw();
       });

      });

Answer 1

.val() returns a string, you need a float:

var dummy = parseFloat($('#xint').val());

Updated fiddle .

EDITS FOR COMMENT

Do not update the tickInterval as you are doing it (it messes with the internals of Highcharts) Instead use:

    chart.yAxis[0].update({
        tickInterval: dummy
    })