Simple Read File Extension

<?php
function isJPG($filename){
    $ext = substr($filename, -4);
    if($ext == '.jpg'){
        return true;
    }else{
        return false;
    }
}
$playlist="";
$d = dir('gambar/');
while (false !== ($filename = $d->read())) {
    if(isJPG($filename)){
        $playlist .= $filename . '|';
		// return data
    }
}
$d->close();
//paging here
?>