[nikita.mmf]

var table = document.getElementById("product_table");
var rows = table.getElementsByTagName("tr");
for ( var i = 0; rows[i]; i++ ) {
  var cells = rows[i].getElementsByTagName("td");
  for ( var j = 0; cells[j]; j++ ) {
    if ( (i + j) % 2 ) {
      cells[j].style.backgroundColor = "#CCC";
    }
  }
}