Untitled

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title></title>
</head>
<style type="text/css">
table {
border-collapse: collapse;
} td {
width: 50px;
height: 50px;
}
.r1 {
background-color: yellow;}
.r2 {
background-color: green;
}
</style>
<body>
<script type="text/javascript">
var str, sel, n = 10, i, j;
document.write("<table>");
for (i = 0; i < n; i++) {
document.write("<tr>");
for (j = 0; j < n; j++) {
sel = (i + j)%3;
if (sel == 0) {
str = "class='r1'";
} else {
str = "class='r2'";
}
document.write("<td " + str + "></td>");
}
}
document.write("</table>");
</script>
</body>
</html>