Shopify - Apply Discount / Coupon / Promo Code on cart page

cart.liquid

<div class="cart-promo">
  <input type="text" id="devPromo" placeholder="Discount Code">
    <a href="/checkout?discount=none" id="redemDevPromo" class="btn" style="margin-bottom:0px">Apply</a></div>
<script>$(document).ready(function() {
    //listen to the promo button click
    $('#redemDevPromo').on('click',
    function(event) {
      //disable the button event
      event.preventDefault();
      //write the url format
      var theUrl = '/checkout?discount=';
      //grab the discount code from the input
      var theDiscount = $('#devPromo').val();
      //full url to redirect to checkout with promo code
      var toRedirect = theUrl + theDiscount;
      console.log(toRedirect);
      //redirect
      window.location.href = toRedirect;
    });
  }); 
</script>

cart.liquid文件中添加

I added to cart.liquid, looks great. When click Apply, go to checkout but coupon shows none.
Any update?