Hello @kartik,
You can do Ajax request to your server with data in request parameters, like this:
jQuery.ajax({
    type: "POST",
    url: 'your_functions_address.php',
    dataType: 'json',
    data: {functionname: 'add', arguments: [1, 2]},
    success: function (obj, textstatus) {
                  if( !('error' in obj) ) {
                      yourVariable = obj.result;
                  }
                  else {
                      console.log(obj.error);
                  }
            }
});
Note that the following code uses jQuery
and your_functions_address.php like this:
    <?php
    header('Content-Type: application/json');
    $aResult = array();
    if( !isset($_POST['functionname']) ) { $aResult['error'] = 'No function name!'; }
    if( !isset($_POST['arguments']) ) { $aResult['error'] = 'No function arguments!'; }
    if( !isset($aResult['error']) ) {
        switch($_POST['functionname']) {
            case 'add':
               if( !is_array($_POST['arguments']) || (count($_POST['arguments']) < 2) ) {
                   $aResult['error'] = 'Error in arguments!';
               }
               else {
                   $aResult['result'] = add(floatval($_POST['arguments'][0]), floatval($_POST['arguments'][1]));
               }
               break;
            default:
               $aResult['error'] = 'Not found function '.$_POST['functionname'].'!';
               break;
        }
    }
    echo json_encode($aResult);
?>
Hope it helps!!
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