var row_class_a = 'row_a';
var row_class_b = 'row_b';
var row_class;
$.getJSON("http://libertyboom.com/leaderboard.php", 
function(data){
  $.each(data.leaderboard.scores, function(i,item){
  	if ( i % 2 ) { row_class = row_class_b } else { row_class = row_class_a };
	$("#global_leader_board").append('<tr class="'+ row_class +'"><td>' + (i+1) + '</td>' 
	  									+ '<td>' + item.nickname + '</td>'
	  									+ '<td>' + item.level + '</td>'
										+ '<td>' + item.score + '</td></tr>'
										);
	if ( (i+1) == 50 ) return false;
  });
});