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.value);
// get the URL
http = new XMLHttpRequest();
http.open("GET", url, true);
http.send(null);
// prevent form from submitting
return false;
}
</script>
<form action="" onsubmit="return submitCouponCode();">
<input type="text" id="couponCode">
<input type="submit" value="Apply">
</form>