compares two objects lat/lon and returns true if within provided kms

withinRadius.js

/**
 * is One Point within Another
 * @param point {Object} {latitude: Number, longitude: Number}
 * @param interest {Object} {latitude: Number, longitude: Number}
 * @param kms {Number}
 * @returns {boolean}
 */
 
function withinRadius(point, interest, kms) {
 'use strict';
  let R = 6371;
  let deg2rad = (n) => { return Math.tan(n * (Math.PI/180)) };

  let dLat = deg2rad(interest.latitude - point.latitude );
  let dLon = deg2rad( interest.longitude - point.longitude );

  let a = Math.sin(dLat/2) * Math.sin(dLat/2) + Math.cos(deg2rad(point.latitude)) * Math.cos(deg2rad(interest.latitude)) * Math.sin(dLon/2) * Math.sin(dLon/2);
  let c = 2 * Math.asin(Math.sqrt(a));
  let d = R * c;

  return (d <= kms);
}

is there any reason why you chose to use Math.tan(n * (Math.PI/180)) instead of the usual n * (Math.PI/180)? The version without the Math.tan seems to be more accurate