Do something after two second of keyup

hope this will help...

 $("#input").keyup(function(){
     var x=$("#input").val();
     setTimeout(function(){
         if(x==$("#input").val()) {
             alert('ajax call going');
         }
     }, 3000);
});

var _changeInterval = null;

$("#input").keyup(function() {
    // wait untill user type in something
    // Don't let call setInterval - clear it, user is still typing
    clearInterval(_changeInterval)
    _changeInterval = setInterval(function() {
        // Typing finished, now you can Do whatever after 2 sec
        clearInterval(_changeInterval)
    }, 2000);

});

Note: Code taken from SO few months back, don't remember the link

Edit:

Check this jsFiddle. Check comments in the Code and output in console for better understading

Try this:

<script src="//code.jquery.com/jquery-1.11.2.min.js"></script>
<input type="text" id="input"> 
<script>
$(document).ready(function(){
    $("#input").keyup(function(){
       var str = $(this).val();
       setTimeout(function(){
            if(str == $("#input").val()) {
                alert('ajax call going');
            }
       }, 2000);
    });
});
</script>