Covert HelloWorld to TSX

app/javascript/bundles/HelloWorld/components/HelloWorld.jsx → app/javascript/bundles/HelloWorld/components/HelloWorld.tsx

@@ -1,7 +1,13 @@
-import PropTypes from 'prop-types';
-import React, { useState } from 'react';
+import * as React from 'react';
+import { useState, FunctionComponent } from 'react';
 
-const HelloWorld = (props) => {
+export interface Props {
+  name: string;
+}
+
+// Note,  you need to declare the type so that ReactOnRails.register has the
+// proper type.
+const HelloWorld: FunctionComponent<Props> = (props: Props) => {
   const [name, setName] = useState(props.name);
 
   return (
@@ -18,8 +24,4 @@ const HelloWorld = (props) => {
   );
 };
 
-HelloWorld.propTypes = {
-  name: PropTypes.string.isRequired, // this is passed from the Rails view
-};
-
 export default HelloWorld;