Haversine formula - calculate distance in metres between two sets of co-ordinates

haversine.js

function CalculateDistance(lat1, lon1, lat2, lon2) {
  function toRad(x) {
    return x * Math.PI / 180;
  }

  let R = 6371000; // set formula in metres

  // Magic
  let x1 = lat2 - lat1;
  let dLat = toRad(x1);
  let x2 = lon2 - lon1;
  let dLon = toRad(x2);
  let a = Math.sin(dLat / 2) * Math.sin(dLat / 2) +
    Math.cos(toRad(lat1)) * Math.cos(toRad(lat2)) *
    Math.sin(dLon / 2) * Math.sin(dLon / 2);
  let c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
  let d = R * c;

  // return value to 2 dp
  return d.toFixed(2);
}