ReactJS: add loading state

- use 8081 port for talking to SpringBoot (as 8080 occupied by Corda)

webapp/package.json

@@ -17,7 +17,7 @@
     "test": "react-scripts test",
     "eject": "react-scripts eject"
   },
-  "proxy": "http://localhost:8080",
+  "proxy": "http://localhost:8081",
   "eslintConfig": {
     "extends": [
       "react-app",

webapp/src/App.js

@@ -3,7 +3,8 @@ import React, { useState, useEffect } from 'react';
 
 function App() {
 
-  const [joke, setJoke] = useState([]);
+  const [joke, setJoke] = useState(null);
+
   useEffect(() => {
     fetch('/api/badjokes')
       .then((response) => response.json())
@@ -20,7 +21,7 @@ function App() {
     <div className="App">
       <header className="App-header">
         <p>
-          Here is your joke: {joke}
+          Here is your joke: {joke ? <span>{joke}</span> : <span>Loading...</span>}
         </p>
       </header>
     </div>