这个程序为啥不执行?请朋友们看看
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
<script type="text/javascript" >
function step()
{
for(i=1;i<=9;i++)
{
for(j=1;j<=i;j++)
{
document.write(i+"x"+j+"="+i*j +" ");
}
document.write("<br/>")
}
}
</script>
</head>
<body>
<form>
<input type ="button" value ="加载乘法表" onclick="step()">
</form>
</body>
</html>