สอบถาม function calculateSum เราจะเพิ่มค่ายังไงครับ

<span id="sum" name="sum">0</span

<script>
	$(document).ready(function(){

		//iterate through each textboxes and add keyup
		//handler to trigger sum event
		$(".for_calc").each(function() {

			$(this).keyup(function(){
				calculateSum();
			});
		});

	});

	function calculateSum() {

		var sum = 0;
		//iterate through each textboxes and add the values
		$(".for_calc").each(function() {

			//add only if the value is number
			if(!isNaN(this.value) && this.value.length!=0) {
				sum += parseFloat(this.value);
			}

		});
		//.toFixed() method will roundoff the final sum to 2 decimal places
		$("#sum").html(sum.toFixed());
	}
</script>

$(xxx).each( function ( idx, object){
   sum+=parseFloat(object.value);
});