javascript - How to avoid a function directing to another page if an entry is incorrect -

i have remove page can remove entry database pre loaded option box. however, redirects 'remove-module-complete.php' page when type in random text. want direct 'remove-module-complete.php' if actual entry database. javascript doesn't seem working.

i have validation entry 'didnt match item' jquery still directs me 'module remove complete' if press submit.

any help?

here php

<?php      if (isset($_post['submit'])){          $modulecode = $_post['modulecode'];         $modulecodelen = strlen($modulecode);         if ($modulecodelen=6){          $sqltwo = "delete modules id = '$modulecode'";           mysql_query($sqltwo);           $restwo =& $db->query($sqltwo);         if(pear::iserror($res)){             $errorvar = ($res->getmessage());             echo "<script type='text/javascript'>alert('invalid entry, please try again. error code: $errorvar');</script>";             die;            }         else echo "<script> location.replace('http://project.ac.uk/remove-module-complete.php'); </script>";     }     else echo "<script type='text/javascript'>alert('invalid entry, please try again');</script>";  } ?>  

seems have errors(commented lines):

if (isset($_post['submit'])) {      $modulecode = $_post['modulecode'];     $modulecodelen = strlen($modulecode);      // '==', not '='     if ($modulecodelen==6) {          $sqltwo = "delete modules id = '$modulecode'";          mysql_query($sqltwo);           $restwo =& $db->query($sqltwo);          // there no $res variable in given part of code         // maybe need use $restwo variable here?         if (pear::iserror($res)) {             $errorvar = ($res->getmessage());             echo "<script type='text/javascript'>alert('invalid entry, please try again. error code: $errorvar');</script>";             die;           }         else echo "<script> location.replace('http://project.ac.uk/remove-module-complete.php'); </script>";     }     else echo "<script type='text/javascript'>alert('invalid entry, please try again');</script>";  }