<script> document.write("<table border=1>");
            for(var i = 1;i <= 9;i++){
                document.write("<tr>");
                for(var j = 1;j <= i;j++){
                    document.write("<td>"+j+"*"+i+"="+j*i+"</td>" );
                }
                document.write("</tr>");
            }
            document.write("</table>");
        
    </script>


求大佬讲解一下这段代码