Calculate distance between LAT LON values

latlon.js

// calculate distance between two LAT LON values
// Note: In this formula, the latitudes and longitudes are expressed in radians. 6371 is radius of the earth in km
// SOURCE: codinggame.com 

var earthRadius = 6371;

var x = (lonB-lonA)*Math.cos((latA+latB)/2);
var y = (latB-latA);
var d = Math.sqrt(x*x+y*y)*earthRadius;