Added framework folder

framework/bigcommerce/api/utils/concat-cookie.ts

@@ -0,0 +1,14 @@
+type Header = string | number | string[] | undefined
+
+export default function concatHeader(prev: Header, val: Header) {
+  if (!val) return prev
+  if (!prev) return val
+
+  if (Array.isArray(prev)) return prev.concat(String(val))
+
+  prev = String(prev)
+
+  if (Array.isArray(val)) return [prev].concat(val)
+
+  return [prev, String(val)]
+}