// If the element's string matches the regular expression it is all numbers
function isNumeric(elem){
	var numericExpression = /^[0-9]+$/;
	if(elem.value.match(numericExpression)){
		return true;
	}else{
		elem.focus();
		return false;
	}
}

function increment_item(item)
{
   var element;
	 element = document.getElementById(item);
   if ( element )
	 {
      if ( isNumeric(element) )
			{
         element.value++;
			}
			else
			{
			  element.value = '1';
			}
   }
}

function decrement_item(item)
{
   var element;
	 element = document.getElementById(item);
   if ( element )
	 {
      if ( isNumeric(element) )
			{
         element.value--;
				 if ( element.value < 0 )
				 {
				     element.value = '0';
				 }
			}
			else
			{
			  element.value = '0';
			}
   }
}