You need to use either the onsubmit
event of the form or the onclick
event of the button.
In the event handler, you assemble a URL and "get" it. For example:
<script type="text/JavaScript">
function submitCouponCode()
{
var textbox = document.getElementById("couponCode");
var url =
"https://www.example.com/script.php?couponCode=" + encodeURIComponent(textbox<span style="border:0px; box-sizing:inherit; color:var(--black-750); font-family:inherit; font-stretch:inherit; font-style:inherit; font-variant:inherit; font-weight:inherit; line-height:inherit; margin:0px; padding:0px; vertical-align:b