jquery click not working

$(document).on( 'click', '.classname', function () { 
alert('clicked');
});

**** Another Method ****
// where #wrapper is a static element in which you add the dynamic links.
$( '#wrapper' ).on( 'click', 'a', function () { alert('clicked'); });

$(document).ready(function() {
  $("#clicker").click(function () {
    alert("Hello!");
    $(".hide_div").hide();
  });
});