Function updateOutdated

Calls the async fn to generate a value if there is no prior value or interval has elapsed since value was last generated.

Example

const f = updateOutdated(async () => {
 const r = await fetch(`blah`);
 return await r.json();
}, 60*1000);

// Result will be JSON from fetch. If fetch happened already in the
// last 60s, return cached result. Otherwise it will fetch data
const result = await f();
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Callback fn is passed how many milliseconds have elapsed since last update. Its minimum value will be interval.

const f = updateOutdated(async elapsedMs => {
 // Do something with elapsedMs?
}, 60*1000;
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There are different policies for what to happen if fn fails. slow is the default.

• fast: Invocation will happen immediately on next attempt
• slow: Next invocation will wait interval as if it was successful
• backoff: Attempts will get slower and slower until next success. Interval is multipled by 1.2 each time.