Really fix it

app/assets/javascripts/orders.js

@@ -52,7 +52,7 @@ ready = function() {
     barcode = $(this).find("input[type=number]").val();
     $("#from_barcode_form")[0].reset();
     $.ajax({
-      url: "/barcodes/" + barcode,
+      url: $("#from_barcode_form").data("url") + "/barcodes/" + barcode,
       success: function(data) {
         if (data != null) {
           increment_product(data["id"]);

app/views/orders/new.html.haml

@@ -2,7 +2,7 @@
   .col-md-6.col-md-offset-1.barcode-wrapper
     .center
       %h1 Order for #{@user.name}
-      = form_tag nil, id: "from_barcode_form" do
+      = form_tag nil, id: "from_barcode_form", data: { url: URI.join(root_url, "barcodes").to_s } do
         %input.center-block{ type: :number, name: :id, autofocus: true }
       = "- OR -"
       %button.btn.btn-default.center-block{ data: { toggle: :modal, target: "#products_modal" } }