Encoding data into an order of a fixed number of array indexes

gistfile1.txt

function getOptions(len) {
   return Array(len).join().split(",").map(function(c, i) {
      return i;
   });
}
function getStep(i, len) {
   return factorial(len) / len * i;
}

function to(order) {
   var remainingOptions = getOptions(order.length);
   var res = 0;
   order.forEach(function(n, i) {
      res += getStep(remainingOptions.indexOf(n), remainingOptions.length)
      remainingOptions.splice(remainingOptions.indexOf(n),1)
   });
   return res;
}

function from(res, len) {
   var remainingOptions = getOptions(len);
   var arr = [];
   for(var i = 0; i < len; i++) {
      var step = getStep(1, remainingOptions.length);
      var n = Math.floor(res/step);
      arr.push(remainingOptions[n]);
      remainingOptions.splice(remainingOptions.indexOf(remainingOptions[n]),1)
      res -= n*step;
   }
   return arr;
}