elo rating

gistfile1.js

function elo(oldRating, opponentRating, result) {
  var kFactor;
  var expected = 1.0 / (1.0 + Math.pow(10.0, ((opponentRating - oldRating) / 400)));
 
  if (oldRating < 2100) {
    kFactor = 32;
  } else if (oldRating >= 2100 && oldRating <= 2400) {
    kFactor = 24;
  }
  else if (oldRating > 2400) {
    kFactor = 16;
  }
   
  return oldRating + kFactor * (result - expected);
}