Haversine.js

function toRadians(degrees) {
  return degrees * (Math.PI / 180);
}

function haversine(lat1, lon1, lat2, lon2) {
  // @dev Earth radius in KM, if you want the final distance in miles change into 3958.8 
  const R = 6371; 
  const dLat = toRadians(lat2 - lat1);
  const dLon = toRadians(lon2 - lon1);

  // @dev a = sin²(φB - φA/2) + cos φA * cos φB * sin²(λB - λA/2)
  const a =
    Math.sin(dLat / 2) * Math.sin(dLat / 2) +
    Math.cos(toRadians(lat1)) * Math.cos(toRadians(lat2)) *
    Math.sin(dLon / 2) * Math.sin(dLon / 2);

  // @dev c = 2 * atan2( √a, √(1−a) )
  const c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));

  // @dev d = R ⋅ c
  const distance = R * c;
  return distance;
}

// @dev example usage
const distance = haversine(52.5200, 13.4050, 48.8566, 2.3522);
console.log(distance);