点击按钮 文本框内不会出现数字！ 求解 哪里错了！
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Math </title>
<script type="text/javascript">
function math(){
var r=Math.round(Math.random()*10);
document.getElementById("b").value=r;
}
</script>
</head>
<body>
<input type="button" id="a" name="" value="随机取数" oclick="math()"/><br/><br/>
<input type="text" id="b" name="" value="" >
</body>
</html>
