I've got the following form set up to allow customers to share a URL with a URL parameter attached to it:
<form action="http://www.facebook.com/sharer.php" method="GET" target="_blank">
<input type="text" id="u" name="u" value="https://www.example.com/page/">
<input type="text" id="code" name="code" placeholder="Enter your code here">
<button type="submit" id="submit">Submit</button>
</form>
However, Facebook strips the ?coupon_code=XXXXXXX URL parameter. Any ideas how I would get around that?