Не работает скрипт замены

jQuery('#quantity').keyup(function(){ 
  if(typeof(window.delayer) != 'undefined') 
    clearTimeout(window.delayer); 
  window.delayer = setTimeout(myFunction, 1000); 
}); 
 
function myFunction() { 
  var val = jQuery('#quantity').val(); 
  alert(val); 
  var p = jQuery('#product_qty').html(); 
  if (val > p) jQuery('#quantity').val(p); 
} 
 
setTimeout(myFunction, 1000);

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script> 
<span id="product_qty">22</span> 
 
   <input name="quantity" id="quantity" oninput="" class="inputbox" value="19" />