diff --git a/src/util/classNames.ts b/src/util/classNames.ts
new file mode 100644
index 0000000000000000000000000000000000000000..2c9f3d9fa7c309028dc8f2afa1c8ed5c0d7e309a
--- /dev/null
+++ b/src/util/classNames.ts
@@ -0,0 +1,3 @@
+export default function classNames (...classes: (string | null | undefined)[]): string {
+  return classes.filter(c => typeof c === "string").join(" ");
+}