createElement ปัญาการเพิ่ม textbox โดยใช้ java script รบกวนช่วยหน่อยครับ

function addCapital(){
	var validator = true;

	if(window.document.getElementById("capital_name").value == ""){
		validator = false;
		alert("กรุณากรอกชื่อทุนดำเนินการ");
	}

	if(!validator)
		return false;

	var tbl = document.getElementById("ajax_capital");
	var lastRow = tbl.rows.length-1;
	var row = tbl.insertRow(lastRow);

	var cell0 = row.insertCell(0);
	var textNode = document.createTextNode(window.document.getElementById("capital_name").value);
	cell0.appendChild(textNode);


	// CELL : member
	var cell1 = row.insertCell(1);
	var textNode = document.createTextNode(window.document.getElementById("capital_amount").value == "" ? 0 : window.document.getElementById("capital_amount").value);
	cell1.style.textAlign = "center";
	cell1.appendChild(textNode);
	
	// CELL : Control
	var cellControl = row.insertCell(2);
	cellControl.style.textAlign = "center";
	var el = document.createElement('input');
	el.type = 'button';
	el.name = 'btn_remove';
	el.value = 'ลบ';
	el.onclick = function(evt){if(confirm("ต้องการลบรายการนี้?")){deleteCurrentRow(el);}};
	cellControl.appendChild(el);
	
	var el = document.createElement('input');
	el.type = 'hidden';
	el.name = 'data[capital][name][]';
	el.value = window.document.getElementById("capital_name").value;
	cellControl.appendChild(el);
	
	var el = document.createElement('input');
	el.type = 'hidden';
	el.name = 'data[capital][amount][]';
	el.value = window.document.getElementById("capital_amount").value == "" ? 0 : window.document.getElementById("capital_amount").value;
	cellControl.appendChild(el);
	
	window.document.getElementById("capital_amount").value = "";
	window.document.getElementById("capital_name").value = "";
	window.document.getElementById("capital_name").focus();
}