js 双层for循环实现九九乘法表

<!-- 九九乘法表 -->
<style>
    span {
        display: inline-block;
        width: 100px;
        height: 30px;
        line-height: 30px;
        text-align: center;
        border: 1px solid #000000;
        margin-left: -1px;
        margin-bottom: -1px;
    }
</style>
<script>
    for (var j = 1; j <= 9; j++) {
        for (var i = 1; i <= j; i++) {
            document.write("<span>" + i + 'x' + j + '=' + i * j + "</span>");
        }
        document.write('<br>')
    }
</script>