Calculate distance between two points on a globe

gistfile1.txt

//PHP
function getDistance($latitude1, $longitude1, $latitude2, $longitude2) {  
    $earth_radius = 6371;  
      
    $dLat = deg2rad($latitude2 - $latitude1);  
    $dLon = deg2rad($longitude2 - $longitude1);  
      
    $a = sin($dLat/2) * sin($dLat/2) + cos(deg2rad($latitude1)) * cos(deg2rad($latitude2)) * sin($dLon/2) * sin($dLon/2);  
    $c = 2 * asin(sqrt($a));  
    $d = $earth_radius * $c;  
      
    return $d;  
} 
//JS
var R = 6371; // km  
var dLat = (lat2-lat1)*Math.PI/180;  
var dLon = (lon2-lon1)*Math.PI/180;   
var a = Math.sin(dLat/2) * Math.sin(dLat/2) +  
        Math.cos(lat1*Math.PI/180) * Math.cos(lat2*Math.PI/180) *   
        Math.sin(dLon/2) * Math.sin(dLon/2);   
var c = 2 * Math.asin(Math.sqrt(a));   
var d = R * c;