calculate distance in kilometers between two points specified by degrees of latitude and longitude

distance.js

/**
 * calculate distance in kilometers between two points specified by degrees of latitude and longitude
 * 
 * @author @kawanet
 * @license MIT
 * @see https://gist.github.com/kawanet/15c5a260ca3b98bd080bb87cdae57230
 * @param {number} lat1 - degree of latitude of origin
 * @param {number} lng1 - degree of longitude of origin
 * @param {number} lat2 - degree of latitude of destination
 * @param {number} lng2 - degree of longitude of destination
 * @return {number} distance in kilometers between origin and destination
 */

function distance(lat1, lng1, lat2, lng2) {
  lat1 *= Math.PI / 180;
  lng1 *= Math.PI / 180;
  lat2 *= Math.PI / 180;
  lng2 *= Math.PI / 180;
  return 6371 * Math.acos(Math.cos(lat1) * Math.cos(lat2) * Math.cos(lng2 - lng1) + Math.sin(lat1) * Math.sin(lat2));
}

if ("undefined" !== exports) exports.distance = distance;