JavaScript code:

        import { ajax } from 'rxjs/observable/dom/ajax';
        import { push } from 'react-router-redux';
        import { Observable } from 'rxjs';


        /** if we are getting a 401 from the API */
        if (isAccessTokenExpired(tokens) && !isRefreshTokenExpired(tokens)) {
            /** POST request to refresh the jwt token */
            return ajax({
                method: 'POST',
                url: REFRESH_ENDPOINT,
                body: JSON.stringify({ refresh: tokens.refresh.token }),
                headers: Object.assign({}, headers, {
                    'Authorization': `Bearer ${tokens.refresh.token}`
                })
            }).flatMap(results => {
                const newTokens = Object.assign({}, tokens, decodeTokens(results.response));
                /** store tokens in redux and local storage */
                storeToken(newTokens);
                /** make the original API request we intended to make in the first place */
                return intendedCall(newTokens);
            });
        } else {
            /** if no 401, just make the API request like normal */
            return intendedCall();
        }