Ajax Response显示并消失

It was working fine. What changes I made, I am unable to trace it out, which has broken it.

But now my Ajax response shows momentarily on the screen and disappear. Using firebug I can see that I am getting the response properly.

I am just been unable to locate, what has gone wrong. This is the code:

<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.1.1/jquery.min.js">
</script>
<script type="text/javascript">
jQuery(document).ready(function($) {
     $('.loader').hide();
$("#domain-check").submit(function (event) {

    /* Stop form from submitting normally */
    event.preventDefault();


    /* Clear result div*/
    $("#result").html('');

    /* Get some values from elements on the page: */
    var values = $(this).serialize();
    $('.loader').show();
    /* Send the data using post and put the results in a div */

    $.ajax({
        url: "?r=site/check",
        type: "post",
        data: values,
        success: function (response) {
           $('.loader').hide();
            $("#result").html(response);
        }
    });
});
});
</script>

and HTML DiV below the form is like this

<div class="loader">
    <span></span>
    <span></span>
    <span></span>
</div> 
<div id="result"></div>

Can it be related to some cache issue?