iBeacon calculate distance in meters

iBeaconCalculateDistance.js

// Based on http://stackoverflow.com/a/20434019

function calculateAccuracy(txPower, rssi) {
  if (rssi === 0) {
    return -1; // if we cannot determine accuracy, return -1.
  }

  var ratio = rssi * 1 / txPower;
  if (ratio < 1.0) {
    return Math.pow(ratio, 10);
  } else {
    return (0.89976) * Math.pow(ratio, 7.7095) + 0.111;
  }
}