Compute the distance between two points using the Haversine formula. See: https://en.wikipedia.org/wiki/Haversine_formula

haversine-distance.js

//
// Compute the distance between two points using the Haversine formula
//
// See: https://en.wikipedia.org/wiki/Haversine_formula
//
// Example: geoCoordDistance(
//   {lat: '48° 12′ 30″ N', lng: '16° 22′ 23″ E'},
//   {lat: '23° 33′ 0″ S', lng: '46° 38′ 0″ W'}
// ) => 10130
//

;(function(global) {
  'use strict';

  /**
   * Polyfill for Number.prototype.toRadians
   */
  if (typeof Number.prototype.toRadians === 'undefined') {
    Number.prototype.toRadians = function() {
      return this * Math.PI / 180;
    }
  }

  /**
   * @var {object} - Regex codes for °, ′, and ″
   */
  const symbols = {
    degrees: unescape('%B0'), // °
    minutes: unescape('%u2032'), // ′
    seconds: unescape('%u2033') // ″
  };

  /**
   * @var {number} - Earth's radius, in kilometers
   */
  const earthRadius = 6371;

  /**
   * Convert lat/lng from DMS to decimal degrees format
   *
   * @param {number} degrees - The degree information
   * @param {number} minutes - The minute information
   * @param {number} seconds - The second information
   * @param {string} cardinalDir - N, S, E, W
   * @return {number} - Decimal format
   */
  const dmsToDecDeg = (degrees, minutes, seconds, cardinalDir) => {
    const decDeg = degrees + (minutes / 60) + (seconds / 3600);
    return (~['N', 'E'].indexOf(cardinalDir)) ? decDeg : -decDeg;
  };

  /**
   * Convert geo coordinate string (e.g. 48° 12′ 30″ N) to a geo coord shaped object
   *
   * @param {string} str - The lat/lng string
   * @return {number} - The value in radians
   */
  const coordStrToObj = str => {
    const degPieces = str.split(symbols.degrees).map(s => s.trim());
    const minPieces = degPieces[1].split(symbols.minutes).map(s => s.trim());
    const secPieces = minPieces[1].split(symbols.seconds).map(s => s.trim());
    const degrees = Number(degPieces[0]);
    const minutes = Number(minPieces[0]);
    const seconds = Number(secPieces[0]);
    const cardinalDir = secPieces[1];
    const decimalDegrees = dmsToDecDeg(degrees, minutes, seconds, cardinalDir);
    const decimalRadians = decimalDegrees.toRadians();
    return {
      decimalDegrees,
      decimalRadians,
      degrees,
      minutes,
      seconds,
      cardinalDir
    };
  };

  /**
   * Given lat and lng string (e.g. 48° 12′ 30″ N), return distance between them in kilometers
   *
   * @param {object} one - The first point
   * @param {string} one.lat - The first point's latitude string
   * @param {string} one.lng - The first point's longitude string
   * @param {object} two - The second point
   * @param {string} two.lat - The second point's latitude string
   * @param {string} two.lng - The second point's longitude string
   * @return {number} - The distance in kilometers
   */
  const geoCoordDistance = (one, two) => {
    const ptOne = {
      lat: coordStrToObj(one.lat),
      lng: coordStrToObj(one.lng)
    };
    const ptTwo = {
      lat: coordStrToObj(two.lat),
      lng: coordStrToObj(two.lng)
    };
    const latDelta = (ptTwo.lat.decimalDegrees - ptOne.lat.decimalDegrees).toRadians();
    const lngDelta = (ptTwo.lng.decimalDegrees - ptOne.lng.decimalDegrees).toRadians();
    const a = (
      Math.pow(Math.sin(latDelta / 2), 2) +
      Math.cos(ptOne.lat.decimalRadians) * Math.cos(ptTwo.lat.decimalRadians) *
      Math.pow(Math.sin(lngDelta / 2), 2)
    );
    const c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
    const d = earthRadius * c;
    // return the distance
    return d;
  };

  // export function to global object
  global.geoCoordDistance = geoCoordDistance;
})(window);