PHP: still work even if not isset

HTML new_password:

   <input name="new_password" type="password" maxlength="25" id="new_password" class="ModuleTextbox" onkeyup="var regex = new RegExp(/^.*(?=.{6,})(?=.*\d)(?=.*[aA-zZ@!¤&amp;/()_?,.-]).*$/m); if(regex.test(this.value)) { pwok.style.visibility = 'visible'; } else { pwok.style.visibility = 'hidden'; }" style="width:200px;" />&nbsp;<img id="pwok" src="ok.png"
                            alt="R" style="visibility: hidden;" />

php after submit form:

foreach开发者_Go百科($_POST as $key => $value) {
    $data[$key] = filter($value);
}
$pw_new = $data["new_password"];


   if(isset($pw_new)) {
echo "LOL";
}

even if i didnt write anything in the field, it echo's LOL, why's that?

---

Because the input is there, the form will still send it even if it's empty. So even if it's empty, it's still set, as in it still exists in $_POST, and so it'll still carry over to $data.

You should use !empty() (that means 'not empty') instead:

if(!empty($pw_new)) {
}

---

Even when you write nothing, you foreach will always set $data["new_password"], then it set $pw_new, you might want so check for values instead of isset

if ($pw_new != '') {
echo 'LOL';
}