JS输出一个矩阵

<script language="javascript">

var arr=[[1,2,3,10],[4,5,6,11],[7,8,9,12]];

for (var i=0;i<arr.length;i++)
{
for (var j=0;j<arr[i].length;j++ )
{
document.writeln(arr[i][j]);
}
document.writeln("<br/>");
}

</script>