How to override parent methods?

[troubled]

So, in the way that our internal application is written, the parent class calls a javascript method that simply displays an alert telling the user that an error has occurred..

In this new app that I am writing, we want to do something different. If a user tries to access this particular page without entering specific request values, then we want to throw an exception. 

So, I define my class and build out my construct method. 

Then I use a method that I have named getData that I am going to post here to give you an idea of where I am with this... In the getData method, I am checking for the request values and if not present, I am trying to throw the exception. Problem is it is not working as I want. Instead, it still throws the javaScript alert from the Parent class. So, I feel like I need to override that Parent method, but not sure how to do so as I am brand new to OOP in PHP. Here's part of my code. I would appreciate any help given.

  public function getData() {
       $qStr = array();

        // get the criteria values from the report template app
        $crit = json_decode($this->getRequestValue("criteria_values"), true);


// THIS IS WHERE I AM TRYING TO THROW THE EXCEPTION.......


        if($crit == "" || $crit == null){
        throw new Exception("Error Processing Request", 1);
        }else{
        if (is_array($crit)) {
            $qStr = array_merge($qStr, $crit);
        }
        $ordLst = array();
        $db = new DbProvider();
        $ret = $db->findWhere("statussheet", $qStr);
        //$trkInfo = $db->findWhere("truckrequests",array("siteid"=>"DET"));
        $trkInfo = $db->findOpen("truckrequests");
        $truckInfo = array();
        $stats = array();
        //$trkInf = json_decode(json_encode($trkInfo), true);
        //  $retArr = json_decode(json_encode($ret), true);
        foreach ($trkInfo->data as $trow) {

            $ordNbr = $trow->detail[0]->ordnbr;
            $truckInfo[$ordNbr] = $trow;
            //$tord = $trow->detail[0]->ordnbr;
          //  var_dump($truckInfo);

        }
        $dets = array();
        foreach($ret->data as $statRow) {
            if (isset($truckInfo[$statRow->ordnbr])) {
                $statRow->covered = "Yes"; //var_export($truckInfo[$statRow->ordnbr], true);

                $statRow->dateship = $truckInfo[$statRow->ordnbr]->dateship;
              //  $statRow->carrier = var_export($truckInfo[$statRow->ordnbr], true);
              $trkDets = 'trknbr='.(string)$truckInfo[$statRow->ordnbr]->detail[0]->trknbr.'&ordnbr=';
              $trkDets .=$ordNbr;
              $statRow->carrier = $truckInfo[$statRow->ordnbr]->detail[0]->trknbr.'<a href = "../../../logistics/TruckList/TruckRequestDocument.php?'.$trkDets.'"target="_blank"><br>See Details</a>';

            }
            else {
                $statRow->covered = "No";
                $statRow->carrier = "Not yet released";
                $statRow->dateship = "Not yet scheduled";
            }
            $statRow->remaining = (float) $statRow->totord - (float) $statRow->shipped;
            if ($statRow->orderstatus != "RDY" && $statRow->orderstatus != "NM") {
            $statRow->orderstatus = "WIP";
            }
            $dets[] = $statRow;
        }
        $ret->data = array_values($dets);
        echo json_encode($ret);

    }
//var_dump($ret->data);
    }


$app = new newStatSheet();
$app->dispatch();

[iarp]

Javascript and PHP are two completely different beasts. You'll need to find out what is triggering the javascript to pop-up, or show where you think the php in the parent element is causing it to appear.