Function updateOutdated

updateOutdated<V>(
    fn: (elapsedMs?: number) => Promise<V>,
    interval: Interval,
    updateFail?: UpdateFailPolicy,
): () => Promise<V>
Calls the async fn to generate a value if there is no prior value or interval has elapsed since value was last generated.
Type Parameters
- V
  Return type of fn
Parameters
- fn: (elapsedMs?: number) => Promise<V>
  Async function to call. Must return a value.
- interval: Interval
  Maximum age of cached result
- updateFail: UpdateFailPolicy = ...
  slow by default
Returns () => Promise<V>
Value
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();
```
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;
```
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.