liat cara pake isset

<?php
/*
perhatikan cara pake isset
*/
session_start();
if(!isset($_SESSION['username'])) {
    echo "<script>alert('YOU MUST LOGIN FIRST');</script>";
    echo "<script>window.location='fpl_login.php'</script>";
}
if(isset($_SESSION['position'])){
    if( $_SESSION['position'] == '1') {
    echo "<script>window.location='op.php'</script>";
    }
    if( $_SESSION['position'] == '2') {
    echo "<script>window.location='foo.php'</script>";
    }
    if( $_SESSION['position'] == '3') {
    echo "<script>window.location='bo.php'</script>";
    }
    if( $_SESSION['position'] == '4') {
    echo "<script>window.location='hq.php'</script>";
    }
}else{
    echo "tak ada session position";
}