Use jsx extension

app/javascript/components/Loadable.jsx

@@ -0,0 +1,24 @@
+import React, { Suspense, lazy } from 'react';
+import PropTypes from 'prop-types';
+
+const Loader = () => <div className="spinner left" />;
+
+function LazyLoad({ component: Component, ...props }) {
+  return (
+    <Suspense fallback={<Loader />}>
+      <Component {...props} />
+    </Suspense>
+  );
+}
+
+LazyLoad.propTypes = {
+  component: PropTypes.object
+};
+
+export default function Loadable(loader) {
+  const LazyComponent = lazy(loader);
+
+  return function PureComponent(props) {
+    return <LazyLoad component={LazyComponent} {...props} />;
+  };
+}