Add discount code to checkout from URL

shopify-discount-from-cookie.js

<script type="text/javascript">
/*
@require
Jquery: https://jquery.com/
jquery-cookie: https://github.com/carhartl/jquery-cookie

Allows you to set a discount code via a URL and pass into shopify checkout

https://myshopifystore.com?coupon=MYCOUPONCODE
can append ?coupon=MYCOUPONCODE to any URL

*/

// Get paramaters from the URL
function getParameterByName(name, url) {
  if (!url) {
    url = window.location.href;
  }

  name = name.replace(/[\[\]]/g, "\\$&");
  var regex = new RegExp("[?&]" + name + "(=([^&#]*)|&|#|$)"),
      results = regex.exec(url);
  if (!results) return null;
  if (!results[2]) return '';
  return decodeURIComponent(results[2].replace(/\+/g, " "));
}

// This must be added to your checkout form 
// <input class="js-form-discount" type="hidden" name="discount" value="RESELLERDISCOUNTCODE" >
$discountInput = $("input.js-form-discount");

// set cookie with passed in coupon code to any URL
$coupon = getParameterByName('coupon');

if($coupon){
  // set a cookie with the coupon code
  // Valid for 7 days : can adjust { expires: 7 } to whatever you want
  // single / is a session cookie
  $.cookie('discountCode', $coupon, { expires: 7 });
}

// Get cookie discount code value and set form value
$discountCode = $.cookie('discountCode');

if($discountCode){
  if ($discountInput.length > 0) { 
    // if cookie is set and discount input field is on page set its value to cookie val 
    $discountInput.val( $discountCode );
  }
}
</script>