Edit in JSFiddle

// This will keep track of the timer
var timer;

$("#startlink").click(function(){
    
    timer = window.setInterval(function(){
        $("#dots").append(". ");
    }, 500);

});

$("#stoplink").click(function(){
    
    window.clearInterval(timer);

});

<a id="startlink" href="#">start</a>
<a id="stoplink" href="#">stop</a>
<div id="dots">. </div>

#dots{
    font-family: monospace;
    font-size: 20px;
}