Calc GPS Distance

gps_distance.js

const toRad = function (number) {
  return number * Math.PI / 180;
}

const calculateDistance = function (lat1, lon1, lat2, lon2) {
  var R = 6371; // 6371 - km | 6371e3 - m
  var dLat = toRad(lat2 - lat1);
  var dLon = toRad(lon2 - lon1);
  var 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);

  var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
  var d = R * c;

  return d;
}

// Usage
// const MAX_DISTANCE = 2;
//
// if (distance <= MAX_DISTANCE) {
//   console.log('Ok');
// }