jwt-fetch.js

```
// src/modules/jwt-fetch.js
let token;

const updateToken = x => { token = x };

const getToken = () => fetch('/api/jwt/token').then(extractTokenFromRes);
const refreshToken = () => fetch('/api/jwt/token/refresh').then(extractTokenFromRes);

const jwtFetch = async (url, opts) => {
  if (!token) { await getToken().then(updateToken); }
  
  return fetch(url, { ... opts, headers: { ...opts.headers, token }})
    .then(res => {
      if (hasTokenExpired(res)) {
        return refreshToken().then(updateToken).then(() => jwtFetch(url, opts))
      }
      return res;
    }
}

export default jwtFetch;
```