<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>div块布局</title>
<script>
function js(){
var x,y,z;
x=document.getElementById('textfield').value;
y=document.getElementById('textfield2').value;
if(x==''){
alert("加数一不能为空！")
return false;
}else{
if(isNaN(x)==true){
alert("加数一请输入数值型！")
return false;
};
};
if(y==''){
alert("加数二不能为空！")
document.getElementById('textfield').value="";
return false;
}else{
if(isNaN(y)==true){
alert("加数二请输入数值型！")
return false;
};
};
z=parseInt(x)+parseInt(y);
document.getElementById('textfield3').value=z;
};
</script>
</head>
<body>
<form action="" method="get">
<table width="300" border="0" align="center" cellpadding="0" cellspacing="0">
<tr>
<th height="30" colspan="2" scope="col">加法计算器</th>
</tr>
<tr>
<td width="50" align="right" valign="middle">加数一：</td>
<td width="150" height="30" align="left" valign="middle"><input type="text" name="textfield" id="textfield"></td>
</tr>
<tr>
<td width="50" height="30" align="right" valign="middle">加数二：</td>
<td width="150" height="30" align="left" valign="middle"><input type="text" name="textfield2" id="textfield2"></td>
</tr>
<tr>
<td width="50" height="30" align="right" valign="middle">加数和：</td>
<td width="150" height="30" align="left" valign="middle"><input type="text" name="textfield3" id="textfield3"></td>
</tr>
<tr>
<td height="30" colspan="2" align="center" valign="middle"><input onClick="js()" type="button" name="button" id="button" value="计算"></td>
</tr>
</table>
</form>
</body>
</html>