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RxJs operator to reload a JWT when it expires
import { MonoTypeOperatorFunction, BehaviorSubject, Observable } from 'rxjs';
import { switchMapTo, tap, shareReplay } from 'rxjs/operators';
import JwtDecode from 'jwt-decode';
* Replays a JWT observable stream. If the JWT's exp passes then the source observable
* will be re triggered automatically to get a new token.
* This replays last value so the token will only update when it expires or because of an
* upstream event, regardless of new subscriptions. Look up shareReplay() for more details.
* @requires exp Token's must contain a exp to be used with this.
export default function autoReloadJwt(): MonoTypeOperatorFunction<string> {
return (input$): Observable<string> => {
// subject which we call next on to trigger source observable which requests a token from api
// behaviour subjects always have a value so it will emit immidiately when subscribed to.
const refreshSubject = new BehaviorSubject<void>(undefined);
let timeout: number;
return refreshSubject.pipe(
tap(jwt => {
// clear old timeout incase new token was not the rsult of the timeout
// set timeout to trigger refresh subject when token expires
const { exp } = JwtDecode<{ exp: number }>(jwt);
timeout = window.setTimeout(() => {;
}, exp * 1000 - new Date().getTime());
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