ES6: port datepicker and util to ES6

Change-Id: I203aa47229e6c4dacd3a33bea39c512f4576a182
diff --git a/vitest.config.js b/vitest.config.js
new file mode 100644
index 0000000..c63c71e
--- /dev/null
+++ b/vitest.config.js
@@ -0,0 +1,10 @@
+import { defineConfig } from 'vitest/config';
+
+export default defineConfig({
+  test: {
+    root: 'dev/js/src-lib',
+    environment: 'jsdom',
+    include: ['*/test/**/*Spec.js'],
+    globals: true
+  }
+});