怎么弹不出窗口啊？请大神进来看看
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>函数传参</title>
<script type="text/JavaScript">
function add3(x,y,z)
{
sum = x + y +z;
document.write(x+"、"+y+"、"+z+"和:"+sum+"<br/>");
}
function add(){
var x = parseInt(prompt('input x:'));
var y = parseInt(prompt('input y:'));
var z = parseInt(prompt('input z:'));
add3(x,y,z);
}
</script>
</head>
<body>
<input type='button', value='click me',onclick='add()'>
</body>
</html>
