获取input里从输入的值（有看到之前的提问，但是没有解决我的问题，希望大神帮忙看看！！！）

可能我的语句有点啰嗦。。。。。我求和的结果出来的一直都是NaN，主要是在shouSum（）里出了错误，求解！！！！
<html>
<head>
<title>javascript软键盘制作</title>
<script language="javascript">
function KeyDisp1(nkey){
if(nkey!=''){
document.KeyForm1.keybox1.value=document.KeyForm1.keybox1.value+nkey;
}
}
function KeyformClr1(){
document.KeyForm1.keybox1.value='';
}
function KeyDisp2(nkey){
if(nkey!=''){
document.KeyForm2.keybox2.value=document.KeyForm2.keybox2.value+nkey;
}
}
function KeyformClr2(){
document.KeyForm2.keybox2.value='';
}
function showSum(){
var number1=parseInt(document.getElementById("keybox1").value);
var number2=parseInt(document.getElementById("keybox2").value);

var number=number1+number2;
var n=number.toString();
document.write("<HR>");
document.write("<form name='Sum'>");
document.write("<input name='sumbox' type='text' size=60>");
document.write('<input type="button" value="SUM" onClick="result('," '",n," ' ",')"><BR>');
document.write("</form>");
document.write("<HR>");

}
function result(n1){
if(n1!="")
document.Sum.sumbox.value=n1;
}
</script>
</head>
<body>
<script language="javascript">
document.write("<HR>");
document.write("<h3>数字软键盘制作</h3>");
document.write("<HR>");
document.write("<form name='KeyForm1'>");
document.write("<input name='keybox1' id='keybox1' type='text' size=60>");
document.write('<input type="button" value="CLR" onClick="KeyformClr1()"><BR>');
var number="0123456789";
for(i=0;i<10;i++){
document.write('<input type="button" value="',number.charAt(i),'" onClick="KeyDisp1('," '",number.charAt(i)," ' ",')">');
}
document.write("</form>");
document.write("<HR>");


document.write("<HR>");
document.write("<form name='KeyForm2'>");
document.write("<input name='keybox2' id='keybox2' type='text' size=60>");
document.write('<input type="button" value="CLR" onClick="KeyformClr2()"><BR>');
for(i=0;i<10;i++){
document.write('<input type="button" value="',number.charAt(i),'" onClick="KeyDisp2('," '",number.charAt(i)," ' ",')">');
}
document.write("</form>");
document.write("<HR>");

document.write(showSum());
</script>
</body>
</html>