Calculate Net Promoter Score

nps.js

// Expects an array of scores from 0-10
// Example: nps([10, 9, 10, 4]); -> 50
// See http://www.medallia.com/net-promoter-score/
function nps(scores) {
  var promoters = 0;
  var detractors = 0;
  
  for (var i=0, l=scores.length; i<l; i++) {
    if (scores[i] >= 9) promoters++;
    if (scores[i] <= 6) detractors++;
  }
  
  return Math.round(((promoters / l) - (detractors / l)) * 100);
}