poll.js

// poll async featch calls in a syncronized fashion, IE do not start the next function call until the previous was resolved.
// also allows for throttling :) 
async function poll(fn, onData, throttle) {
    const _throttle = throttle || 5000;
    let lastPollStarted;
    async function _poll(_fn, _onData) {
        lastPollStarted = new Date().getTime();
        let response = await _fn();
        if (response.status === 200) {
            // Get and show the message
            var stopPolling = onData(response);
            if (stopPolling) {
                return;
            }
            const lastPollFinished = new Date().getTime();
            const elapsed = lastPollFinished - lastPollStarted;
            if (elapsed < _throttle) {
                await new Promise(resolve => setTimeout(resolve, _throttle - elapsed));
            }
            // Call subscribe() again to get the next message
            await _poll(_fn, _onData);
        }
        else {
            console.error("Got non-200 response while polling: ", response);
        }
    }
    _poll(fn, onData);
}

// USAGE

async function getGoogle() {
  const googleResponse = await fetch("/")
  return googleResponse;
}

poll(getGoogle, (response) => console.log(response))