is it possible to set a PHP variable using a drop down menu but without having to go to another page?

I know that with javascript I can load another page when an item is selected from a drop down menu without having to actually click a "submit" button, I would like to do the same (submitting without having to click a submit button) but I would like to set a PHP variable instead of going somewhere...

to paraphrase what I want to do:

<select name="var">
<option>var 1</option> // when chosen it will set $var = 1;
<option>var 3</option> // when chosen it will set $var = 2;
</select>

Thanks

    <form action="" method="post">
<select name="var" onchange="this.form.submit();">
<option value="1">var 1</option>
<option value="2">var 2</option>
<option value="3">var 3</option>
<option value="4">var 4</option>
<option value="5">var 5</option>
</select>
</form>

<?php
if (isset($_POST['var'])) {echo 'var is now set to ' . $_POST['var'];}
?>
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