gistfile1.txt

var obj = { sets: [] };
var sets = [0,1,2,3,4,5,6,7,8,9,10,11,12,13];
var from = 5;
var size = 5;

for(var i = from; (i < (from + size)) && (i < sets.length); i++) {
  obj.sets.push(sets[i]);
}

console.log(obj.sets);