How to check if a request is sent using ajax or not - PHP Snippet

Simple php function that let you check whether request is sent via ajax or not.

/*************************************************************************** 
* 
*    isAjax 
*    checks whether request is received via ajax call or not 
*    $_SERVER['HTTP_X_REQUESTED_WITH'] is pivotal here 
*    If request is via ajax, returns true 
*    If request is not via ajax, returns false 
* 
***************************************************************************/ 
public function isAjax(){ 
    if(!empty($_SERVER['HTTP_X_REQUESTED_WITH']) &&  
        strtolower($_SERVER['HTTP_X_REQUESTED_WITH']) == 'xmlhttprequest') { 

        // It is an ajax call 
        return true; 
    } 
    else{ 
        // It is not an ajax call 
        return false; 
    } 
}