Interface FetchOptions<K, V, FC>

Allow LRUCache#get and LRUCache#fetch calls to return stale data, if available.

Set to true to return a stale value from the cache when the AbortSignal passed to the OptionsBase.fetchMethod dispatches an 'abort' event, whether user-triggered, or due to internal cache behavior.

Unless OptionsBase.ignoreFetchAbort is also set, the underlying OptionsBase.fetchMethod will still be considered canceled, and any value it returns will be ignored and not cached.

Caveat: since fetches are aborted when a new value is explicitly set in the cache, this can lead to fetch returning a stale value, since that was the fallback value at the moment the fetch() was initiated, even though the new updated value is now present in the cache.

For example:

const cache = new LRUCache<string, any>({
  ttl: 100,
  fetchMethod: async (url, oldValue, { signal }) =>  {
    const res = await fetch(url, { signal })
    return await res.json()
  }
})
cache.set('https://example.com/', { some: 'data' })
// 100ms go by...
const result = cache.fetch('https://example.com/')
cache.set('https://example.com/', { other: 'thing' })
console.log(await result) // { some: 'data' }
console.log(cache.get('https://example.com/')) // { other: 'thing' }
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Set to true to allow returning stale data when a OptionsBase.fetchMethod throws an error or returns a rejected promise.

This differs from using OptionsBase.allowStale in that stale data will ONLY be returned in the case that the LRUCache#fetch fails, not any other times.

Set to true to ignore the abort event emitted by the AbortSignal object passed to OptionsBase.fetchMethod, and still cache the resulting resolution value, as long as it is not undefined.

When used on its own, this means aborted LRUCache#fetch calls are not immediately resolved or rejected when they are aborted, and instead take the full time to await.

When used with OptionsBase.allowStaleOnFetchAbort, aborted LRUCache#fetch calls will resolve immediately to their stale cached value or undefined, and will continue to process and eventually update the cache when they resolve, as long as the resulting value is not undefined, thus supporting a "return stale on timeout while refreshing" mechanism by passing AbortSignal.timeout(n) as the signal.

Note: regardless of this setting, an abort event is still emitted on the AbortSignal object, so may result in invalid results when passed to other underlying APIs that use AbortSignals.

This may be overridden in the OptionsBase.fetchMethod or the call to LRUCache#fetch.

Set to true to suppress the deletion of stale data when a OptionsBase.fetchMethod returns a rejected promise.

Do not delete stale items when they are retrieved with LRUCache#get.

Note that the get return value will still be undefined unless OptionsBase.allowStale is true.

Set to true to suppress calling the OptionsBase.dispose function if the entry key is still accessible within the cache. This may be overridden by passing an options object to LRUCache#set.

Boolean flag to tell the cache to not update the TTL when setting a new value for an existing key (ie, when updating a value rather than inserting a new value). Note that the TTL value is always set (if provided) when adding a new entry into the cache.

Has no effect if a OptionsBase.ttl is not set.

A function that returns a number indicating the item's size.

If not provided, and OptionsBase.maxSize or OptionsBase.maxEntrySize are set, then all LRUCache#set calls must provide an explicit SetOptions.size or sizeCalculation param.

Max time in milliseconds for items to live in cache before they are considered stale. Note that stale items are NOT preemptively removed by default, and MAY live in the cache long after they have expired.

Also, as this cache is optimized for LRU/MRU operations, some of the staleness/TTL checks will reduce performance, as they will incur overhead by deleting items.

Must be an integer number of ms. If set to 0, this indicates "no TTL"

Default

0
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Update the age of items on LRUCache#get, renewing their TTL

Has no effect if OptionsBase.ttl is not set.

Default

false
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