Haversine to calculate distance between two pairs pf latitutde and longitude, plus a bearing function

Haversine.js

// haversine
// By Nick Justice (niix)
// https://github.com/niix/haversine
//
// Corroborated using: http://andrew.hedges.name/experiments/haversine/
import {Waypoint} from "./Waypoint"  // Implement https://developer.mozilla.org/en-US/docs/Web/API/Position/coords

module.exports = {
  // convert to radians
  toRad(num) {
    return num * Math.PI / 180;
  },

  /// Radians to degrees
  toDeg(radians) {
    return radians * (180 / Math.PI);
  },

  /// Returns bearing in degrees range 0 - 360
  /// waypoint objects implement https://developer.mozilla.org/en-US/docs/Web/API/Position/coords
  waypointBearingDegrees(waypointStart, waypointEnd) {
    if(waypointStart == null) {
      return -1.0;
    }
    if(waypointEnd == null) {
      return -1.0;
    }
    if(false == waypointEnd.gpsFixed) {
      return -1.0;
    }

    var dLon = this.toRad(waypointEnd.position.coords.longitude - waypointStart.position.coords.longitude)
    var lat1 = this.toRad(waypointStart.position.coords.latitude)
    var lat2 = this.toRad(waypointEnd.position.coords.latitude)

    var y = Math.sin(dLon) * Math.cos(lat2);
    var x = Math.cos(lat1)*Math.sin(lat2) -
    Math.sin(lat1)*Math.cos(lat2)*Math.cos(dLon);
    var bearing = this.toDeg(Math.atan2(y, x))
    bearing = 360 - ((bearing + 360) % 360);
    return bearing;
  },

  
  // Returns meters by default
  haversine(start, end, options) {
    if(start == null) {
      console.log('start: null');
      return;
    }
    if(end == null) {
      console.log('end: null');
      return;
    }

    var m    = 6371*1000;
    var km    = 6371
    var mile  = 3960
    options   = options || {}

    var R = m;
    if(options.unit === 'mile') {
      R = mile;
    } else if(options.unit === 'km') {
      R = km;
    }

    var dLat = this.toRad(end.latitude - start.latitude)
    var dLon = this.toRad(end.longitude - start.longitude)
    var lat1 = this.toRad(start.latitude)
    var lat2 = this.toRad(end.latitude)

    var a = Math.sin(dLat/2) * Math.sin(dLat/2) +
    Math.sin(dLon/2) * Math.sin(dLon/2) * Math.cos(lat1) * Math.cos(lat2)
    var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a))

    if (options.threshold) {
      return options.threshold > (R * c)
    } else {
      return R * c
    }
  },

}