refactor: Still trying to reorganize edit mode to be more robust

node_modules/tldts-core/src/subdomain.ts

@@ -0,0 +1,11 @@
+/**
+ * Returns the subdomain of a hostname string
+ */
+export default function getSubdomain(hostname: string, domain: string): string {
+  // If `hostname` and `domain` are the same, then there is no sub-domain
+  if (domain.length === hostname.length) {
+    return '';
+  }
+
+  return hostname.slice(0, -domain.length - 1);
+}