840 lines
28 KiB
Markdown
840 lines
28 KiB
Markdown
|
# lru-cache
|
||
|
|
||
|
A cache object that deletes the least-recently-used items.
|
||
|
|
||
|
Specify a max number of the most recently used items that you
|
||
|
want to keep, and this cache will keep that many of the most
|
||
|
recently accessed items.
|
||
|
|
||
|
This is not primarily a TTL cache, and does not make strong TTL
|
||
|
guarantees. There is no preemptive pruning of expired items by
|
||
|
default, but you _may_ set a TTL on the cache or on a single
|
||
|
`set`. If you do so, it will treat expired items as missing, and
|
||
|
delete them when fetched. If you are more interested in TTL
|
||
|
caching than LRU caching, check out
|
||
|
[@isaacs/ttlcache](http://npm.im/@isaacs/ttlcache).
|
||
|
|
||
|
As of version 7, this is one of the most performant LRU
|
||
|
implementations available in JavaScript, and supports a wide
|
||
|
diversity of use cases. However, note that using some of the
|
||
|
features will necessarily impact performance, by causing the
|
||
|
cache to have to do more work. See the "Performance" section
|
||
|
below.
|
||
|
|
||
|
## Installation
|
||
|
|
||
|
```bash
|
||
|
npm install lru-cache --save
|
||
|
```
|
||
|
|
||
|
## Usage
|
||
|
|
||
|
```js
|
||
|
const LRU = require('lru-cache')
|
||
|
|
||
|
// At least one of 'max', 'ttl', or 'maxSize' is required, to prevent
|
||
|
// unsafe unbounded storage.
|
||
|
//
|
||
|
// In most cases, it's best to specify a max for performance, so all
|
||
|
// the required memory allocation is done up-front.
|
||
|
//
|
||
|
// All the other options are optional, see the sections below for
|
||
|
// documentation on what each one does. Most of them can be
|
||
|
// overridden for specific items in get()/set()
|
||
|
const options = {
|
||
|
max: 500,
|
||
|
|
||
|
// for use with tracking overall storage size
|
||
|
maxSize: 5000,
|
||
|
sizeCalculation: (value, key) => {
|
||
|
return 1
|
||
|
},
|
||
|
|
||
|
// for use when you need to clean up something when objects
|
||
|
// are evicted from the cache
|
||
|
dispose: (value, key) => {
|
||
|
freeFromMemoryOrWhatever(value)
|
||
|
},
|
||
|
|
||
|
// how long to live in ms
|
||
|
ttl: 1000 * 60 * 5,
|
||
|
|
||
|
// return stale items before removing from cache?
|
||
|
allowStale: false,
|
||
|
|
||
|
updateAgeOnGet: false,
|
||
|
updateAgeOnHas: false,
|
||
|
|
||
|
// async method to use for cache.fetch(), for
|
||
|
// stale-while-revalidate type of behavior
|
||
|
fetchMethod: async (key, staleValue, { options, signal }) => {}
|
||
|
}
|
||
|
|
||
|
const cache = new LRU(options)
|
||
|
|
||
|
cache.set("key", "value")
|
||
|
cache.get("key") // "value"
|
||
|
|
||
|
// non-string keys ARE fully supported
|
||
|
// but note that it must be THE SAME object, not
|
||
|
// just a JSON-equivalent object.
|
||
|
var someObject = { a: 1 }
|
||
|
cache.set(someObject, 'a value')
|
||
|
// Object keys are not toString()-ed
|
||
|
cache.set('[object Object]', 'a different value')
|
||
|
assert.equal(cache.get(someObject), 'a value')
|
||
|
// A similar object with same keys/values won't work,
|
||
|
// because it's a different object identity
|
||
|
assert.equal(cache.get({ a: 1 }), undefined)
|
||
|
|
||
|
cache.clear() // empty the cache
|
||
|
```
|
||
|
|
||
|
If you put more stuff in it, then items will fall out.
|
||
|
|
||
|
## Options
|
||
|
|
||
|
### `max`
|
||
|
|
||
|
The maximum number of items that remain in the cache (assuming no
|
||
|
TTL pruning or explicit deletions). Note that fewer items may be
|
||
|
stored if size calculation is used, and `maxSize` is exceeded.
|
||
|
This must be a positive finite intger.
|
||
|
|
||
|
At least one of `max`, `maxSize`, or `TTL` is required. This
|
||
|
must be a positive integer if set.
|
||
|
|
||
|
**It is strongly recommended to set a `max` to prevent unbounded
|
||
|
growth of the cache.** See "Storage Bounds Safety" below.
|
||
|
|
||
|
### `maxSize`
|
||
|
|
||
|
Set to a positive integer to track the sizes of items added to
|
||
|
the cache, and automatically evict items in order to stay below
|
||
|
this size. Note that this may result in fewer than `max` items
|
||
|
being stored.
|
||
|
|
||
|
Attempting to add an item to the cache whose calculated size is
|
||
|
greater that this amount will be a no-op. The item will not be
|
||
|
cached, and no other items will be evicted.
|
||
|
|
||
|
Optional, must be a positive integer if provided.
|
||
|
|
||
|
Sets `maxItemSize` to the same value, unless a different value is
|
||
|
provided for `maxItemSize`.
|
||
|
|
||
|
At least one of `max`, `maxSize`, or `TTL` is required. This
|
||
|
must be a positive integer if set.
|
||
|
|
||
|
Even if size tracking is enabled, **it is strongly recommended to
|
||
|
set a `max` to prevent unbounded growth of the cache.** See
|
||
|
"Storage Bounds Safety" below.
|
||
|
|
||
|
### `maxEntrySize`
|
||
|
|
||
|
Set to a positive integer to track the sizes of items added to
|
||
|
the cache, and prevent caching any item over a given size.
|
||
|
Attempting to add an item whose calculated size is greater than
|
||
|
this amount will be a no-op. The item will not be cached, and no
|
||
|
other items will be evicted.
|
||
|
|
||
|
Optional, must be a positive integer if provided. Defaults to
|
||
|
the value of `maxSize` if provided.
|
||
|
|
||
|
### `sizeCalculation`
|
||
|
|
||
|
Function used to calculate the size of stored items. If you're
|
||
|
storing strings or buffers, then you probably want to do
|
||
|
something like `n => n.length`. The item is passed as the first
|
||
|
argument, and the key is passed as the second argument.
|
||
|
|
||
|
This may be overridden by passing an options object to
|
||
|
`cache.set()`.
|
||
|
|
||
|
Requires `maxSize` to be set. If the resulting calculated size
|
||
|
is greater than `maxSize`, then the item will not be added to the
|
||
|
cache.
|
||
|
|
||
|
Deprecated alias: `length`
|
||
|
|
||
|
### `fetchMethod`
|
||
|
|
||
|
Function that is used to make background asynchronous fetches.
|
||
|
Called with `fetchMethod(key, staleValue, { signal, options,
|
||
|
context })`. May return a Promise.
|
||
|
|
||
|
If `fetchMethod` is not provided, then `cache.fetch(key)` is
|
||
|
equivalent to `Promise.resolve(cache.get(key))`.
|
||
|
|
||
|
The `signal` object is an `AbortSignal` if that's available in
|
||
|
the global object, otherwise it's a pretty close polyfill.
|
||
|
|
||
|
If at any time, `signal.aborted` is set to `true`, or if the
|
||
|
`signal.onabort` method is called, or if it emits an `'abort'`
|
||
|
event which you can listen to with `addEventListener`, then that
|
||
|
means that the fetch should be abandoned. This may be passed
|
||
|
along to async functions aware of AbortController/AbortSignal
|
||
|
behavior.
|
||
|
|
||
|
The `options` object is a union of the options that may be
|
||
|
provided to `set()` and `get()`. If they are modified, then that
|
||
|
will result in modifying the settings to `cache.set()` when the
|
||
|
value is resolved. For example, a DNS cache may update the TTL
|
||
|
based on the value returned from a remote DNS server by changing
|
||
|
`options.ttl` in the `fetchMethod`.
|
||
|
|
||
|
### `fetchContext`
|
||
|
|
||
|
Arbitrary data that can be passed to the `fetchMethod` as the
|
||
|
`context` option.
|
||
|
|
||
|
Note that this will only be relevant when the `cache.fetch()`
|
||
|
call needs to call `fetchMethod()`. Thus, any data which will
|
||
|
meaningfully vary the fetch response needs to be present in the
|
||
|
key. This is primarily intended for including `x-request-id`
|
||
|
headers and the like for debugging purposes, which do not affect
|
||
|
the `fetchMethod()` response.
|
||
|
|
||
|
### `noDeleteOnFetchRejection`
|
||
|
|
||
|
If a `fetchMethod` throws an error or returns a rejected promise,
|
||
|
then by default, any existing stale value will be removed from
|
||
|
the cache.
|
||
|
|
||
|
If `noDeleteOnFetchRejection` is set to `true`, then this
|
||
|
behavior is suppressed, and the stale value remains in the cache
|
||
|
in the case of a rejected `fetchMethod`.
|
||
|
|
||
|
This is important in cases where a `fetchMethod` is _only_ called
|
||
|
as a background update while the stale value is returned, when
|
||
|
`allowStale` is used.
|
||
|
|
||
|
This may be set in calls to `fetch()`, or defaulted on the
|
||
|
constructor.
|
||
|
|
||
|
### `dispose`
|
||
|
|
||
|
Function that is called on items when they are dropped from the
|
||
|
cache, as `this.dispose(value, key, reason)`.
|
||
|
|
||
|
This can be handy if you want to close file descriptors or do
|
||
|
other cleanup tasks when items are no longer stored in the cache.
|
||
|
|
||
|
**NOTE**: It is called *before* the item has been fully removed
|
||
|
from the cache, so if you want to put it right back in, you need
|
||
|
to wait until the next tick. If you try to add it back in during
|
||
|
the `dispose()` function call, it will break things in subtle and
|
||
|
weird ways.
|
||
|
|
||
|
Unlike several other options, this may _not_ be overridden by
|
||
|
passing an option to `set()`, for performance reasons. If
|
||
|
disposal functions may vary between cache entries, then the
|
||
|
entire list must be scanned on every cache swap, even if no
|
||
|
disposal function is in use.
|
||
|
|
||
|
The `reason` will be one of the following strings, corresponding
|
||
|
to the reason for the item's deletion:
|
||
|
|
||
|
* `evict` Item was evicted to make space for a new addition
|
||
|
* `set` Item was overwritten by a new value
|
||
|
* `delete` Item was removed by explicit `cache.delete(key)` or by
|
||
|
calling `cache.clear()`, which deletes everything.
|
||
|
|
||
|
The `dispose()` method is _not_ called for canceled calls to
|
||
|
`fetchMethod()`. If you wish to handle evictions, overwrites,
|
||
|
and deletes of in-flight asynchronous fetches, you must use the
|
||
|
`AbortSignal` provided.
|
||
|
|
||
|
Optional, must be a function.
|
||
|
|
||
|
### `disposeAfter`
|
||
|
|
||
|
The same as `dispose`, but called _after_ the entry is completely
|
||
|
removed and the cache is once again in a clean state.
|
||
|
|
||
|
It is safe to add an item right back into the cache at this
|
||
|
point. However, note that it is _very_ easy to inadvertently
|
||
|
create infinite recursion in this way.
|
||
|
|
||
|
The `disposeAfter()` method is _not_ called for canceled calls to
|
||
|
`fetchMethod()`. If you wish to handle evictions, overwrites,
|
||
|
and deletes of in-flight asynchronous fetches, you must use the
|
||
|
`AbortSignal` provided.
|
||
|
|
||
|
### `noDisposeOnSet`
|
||
|
|
||
|
Set to `true` to suppress calling the `dispose()` function if the
|
||
|
entry key is still accessible within the cache.
|
||
|
|
||
|
This may be overridden by passing an options object to
|
||
|
`cache.set()`.
|
||
|
|
||
|
Boolean, default `false`. Only relevant if `dispose` or
|
||
|
`disposeAfter` options are set.
|
||
|
|
||
|
### `ttl`
|
||
|
|
||
|
Max time to live for items before they are considered stale.
|
||
|
Note that stale items are NOT preemptively removed by default,
|
||
|
and MAY live in the cache, contributing to its LRU max, long
|
||
|
after they have expired.
|
||
|
|
||
|
Also, as this cache is optimized for LRU/MRU operations, some of
|
||
|
the staleness/TTL checks will reduce performance.
|
||
|
|
||
|
This is not primarily a TTL cache, and does not make strong TTL
|
||
|
guarantees. There is no pre-emptive pruning of expired items,
|
||
|
but you _may_ set a TTL on the cache, and it will treat expired
|
||
|
items as missing when they are fetched, and delete them.
|
||
|
|
||
|
Optional, but must be a positive integer in ms if specified.
|
||
|
|
||
|
This may be overridden by passing an options object to
|
||
|
`cache.set()`.
|
||
|
|
||
|
At least one of `max`, `maxSize`, or `TTL` is required. This
|
||
|
must be a positive integer if set.
|
||
|
|
||
|
Even if ttl tracking is enabled, **it is strongly recommended to
|
||
|
set a `max` to prevent unbounded growth of the cache.** See
|
||
|
"Storage Bounds Safety" below.
|
||
|
|
||
|
If ttl tracking is enabled, and `max` and `maxSize` are not set,
|
||
|
and `ttlAutopurge` is not set, then a warning will be emitted
|
||
|
cautioning about the potential for unbounded memory consumption.
|
||
|
|
||
|
Deprecated alias: `maxAge`
|
||
|
|
||
|
### `noUpdateTTL`
|
||
|
|
||
|
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.
|
||
|
|
||
|
This may be passed as an option to `cache.set()`.
|
||
|
|
||
|
Boolean, default false.
|
||
|
|
||
|
### `ttlResolution`
|
||
|
|
||
|
Minimum amount of time in ms in which to check for staleness.
|
||
|
Defaults to `1`, which means that the current time is checked at
|
||
|
most once per millisecond.
|
||
|
|
||
|
Set to `0` to check the current time every time staleness is
|
||
|
tested.
|
||
|
|
||
|
Note that setting this to a higher value _will_ improve
|
||
|
performance somewhat while using ttl tracking, albeit at the
|
||
|
expense of keeping stale items around a bit longer than intended.
|
||
|
|
||
|
### `ttlAutopurge`
|
||
|
|
||
|
Preemptively remove stale items from the cache.
|
||
|
|
||
|
Note that this may _significantly_ degrade performance,
|
||
|
especially if the cache is storing a large number of items. It
|
||
|
is almost always best to just leave the stale items in the cache,
|
||
|
and let them fall out as new items are added.
|
||
|
|
||
|
Note that this means that `allowStale` is a bit pointless, as
|
||
|
stale items will be deleted almost as soon as they expire.
|
||
|
|
||
|
Use with caution!
|
||
|
|
||
|
Boolean, default `false`
|
||
|
|
||
|
### `allowStale`
|
||
|
|
||
|
By default, if you set `ttl`, it'll only delete stale items from
|
||
|
the cache when you `get(key)`. That is, it's not preemptively
|
||
|
pruning items.
|
||
|
|
||
|
If you set `allowStale:true`, it'll return the stale value as
|
||
|
well as deleting it. If you don't set this, then it'll return
|
||
|
`undefined` when you try to get a stale entry.
|
||
|
|
||
|
Note that when a stale entry is fetched, _even if it is returned
|
||
|
due to `allowStale` being set_, it is removed from the cache
|
||
|
immediately. You can immediately put it back in the cache if you
|
||
|
wish, thus resetting the TTL.
|
||
|
|
||
|
This may be overridden by passing an options object to
|
||
|
`cache.get()`. The `cache.has()` method will always return
|
||
|
`false` for stale items.
|
||
|
|
||
|
Boolean, default false, only relevant if `ttl` is set.
|
||
|
|
||
|
Deprecated alias: `stale`
|
||
|
|
||
|
### `noDeleteOnStaleGet`
|
||
|
|
||
|
When using time-expiring entries with `ttl`, by default stale
|
||
|
items will be removed from the cache when the key is accessed
|
||
|
with `cache.get()`.
|
||
|
|
||
|
Setting `noDeleteOnStaleGet` to `true` will cause stale items to
|
||
|
remain in the cache, until they are explicitly deleted with
|
||
|
`cache.delete(key)`, or retrieved with `noDeleteOnStaleGet` set
|
||
|
to `false`.
|
||
|
|
||
|
This may be overridden by passing an options object to
|
||
|
`cache.get()`.
|
||
|
|
||
|
Boolean, default false, only relevant if `ttl` is set.
|
||
|
|
||
|
### `updateAgeOnGet`
|
||
|
|
||
|
When using time-expiring entries with `ttl`, setting this to
|
||
|
`true` will make each item's age reset to 0 whenever it is
|
||
|
retrieved from cache with `get()`, causing it to not expire. (It
|
||
|
can still fall out of cache based on recency of use, of course.)
|
||
|
|
||
|
This may be overridden by passing an options object to
|
||
|
`cache.get()`.
|
||
|
|
||
|
Boolean, default false, only relevant if `ttl` is set.
|
||
|
|
||
|
### `updateAgeOnHas`
|
||
|
|
||
|
When using time-expiring entries with `ttl`, setting this to
|
||
|
`true` will make each item's age reset to 0 whenever its presence
|
||
|
in the cache is checked with `has()`, causing it to not expire.
|
||
|
(It can still fall out of cache based on recency of use, of
|
||
|
course.)
|
||
|
|
||
|
This may be overridden by passing an options object to
|
||
|
`cache.has()`.
|
||
|
|
||
|
Boolean, default false, only relevant if `ttl` is set.
|
||
|
|
||
|
## API
|
||
|
|
||
|
### `new LRUCache(options)`
|
||
|
|
||
|
Create a new LRUCache. All options are documented above, and are
|
||
|
on the cache as public members.
|
||
|
|
||
|
### `cache.max`, `cache.maxSize`, `cache.allowStale`,
|
||
|
`cache.noDisposeOnSet`, `cache.sizeCalculation`, `cache.dispose`,
|
||
|
`cache.maxSize`, `cache.ttl`, `cache.updateAgeOnGet`,
|
||
|
`cache.updateAgeOnHas`
|
||
|
|
||
|
All option names are exposed as public members on the cache
|
||
|
object.
|
||
|
|
||
|
These are intended for read access only. Changing them during
|
||
|
program operation can cause undefined behavior.
|
||
|
|
||
|
### `cache.size`
|
||
|
|
||
|
The total number of items held in the cache at the current
|
||
|
moment.
|
||
|
|
||
|
### `cache.calculatedSize`
|
||
|
|
||
|
The total size of items in cache when using size tracking.
|
||
|
|
||
|
### `set(key, value, [{ size, sizeCalculation, ttl, noDisposeOnSet, start }])`
|
||
|
|
||
|
Add a value to the cache.
|
||
|
|
||
|
Optional options object may contain `ttl` and `sizeCalculation`
|
||
|
as described above, which default to the settings on the cache
|
||
|
object.
|
||
|
|
||
|
If `start` is provided, then that will set the effective start
|
||
|
time for the TTL calculation. Note that this must be a previous
|
||
|
value of `performance.now()` if supported, or a previous value of
|
||
|
`Date.now()` if not.
|
||
|
|
||
|
Options object my also include `size`, which will prevent calling
|
||
|
the `sizeCalculation` function and just use the specified number
|
||
|
if it is a positive integer, and `noDisposeOnSet` which will
|
||
|
prevent calling a `dispose` function in the case of overwrites.
|
||
|
|
||
|
If the `size` (or return value of `sizeCalculation`) is greater
|
||
|
than `maxSize`, then the item will not be added to the cache.
|
||
|
|
||
|
Will update the recency of the entry.
|
||
|
|
||
|
Returns the cache object.
|
||
|
|
||
|
### `get(key, { updateAgeOnGet, allowStale } = {}) => value`
|
||
|
|
||
|
Return a value from the cache.
|
||
|
|
||
|
Will update the recency of the cache entry found.
|
||
|
|
||
|
If the key is not found, `get()` will return `undefined`. This
|
||
|
can be confusing when setting values specifically to `undefined`,
|
||
|
as in `cache.set(key, undefined)`. Use `cache.has()` to
|
||
|
determine whether a key is present in the cache at all.
|
||
|
|
||
|
### `async fetch(key, { updateAgeOnGet, allowStale, size, sizeCalculation, ttl, noDisposeOnSet, forceRefresh } = {}) => Promise`
|
||
|
|
||
|
If the value is in the cache and not stale, then the returned
|
||
|
Promise resolves to the value.
|
||
|
|
||
|
If not in the cache, or beyond its TTL staleness, then
|
||
|
`fetchMethod(key, staleValue, options)` is called, and the value
|
||
|
returned will be added to the cache once resolved.
|
||
|
|
||
|
If called with `allowStale`, and an asynchronous fetch is
|
||
|
currently in progress to reload a stale value, then the former
|
||
|
stale value will be returned.
|
||
|
|
||
|
If called with `forceRefresh`, then the cached item will be
|
||
|
re-fetched, even if it is not stale. However, if `allowStale` is
|
||
|
set, then the old value will still be returned. This is useful
|
||
|
in cases where you want to force a reload of a cached value. If
|
||
|
a background fetch is already in progress, then `forceRefresh`
|
||
|
has no effect.
|
||
|
|
||
|
Multiple fetches for the same `key` will only call `fetchMethod`
|
||
|
a single time, and all will be resolved when the value is
|
||
|
resolved, even if different options are used.
|
||
|
|
||
|
If `fetchMethod` is not specified, then this is effectively an
|
||
|
alias for `Promise.resolve(cache.get(key))`.
|
||
|
|
||
|
When the fetch method resolves to a value, if the fetch has not
|
||
|
been aborted due to deletion, eviction, or being overwritten,
|
||
|
then it is added to the cache using the options provided.
|
||
|
|
||
|
### `peek(key, { allowStale } = {}) => value`
|
||
|
|
||
|
Like `get()` but doesn't update recency or delete stale items.
|
||
|
|
||
|
Returns `undefined` if the item is stale, unless `allowStale` is
|
||
|
set either on the cache or in the options object.
|
||
|
|
||
|
### `has(key, { updateAgeOnHas } = {}) => Boolean`
|
||
|
|
||
|
Check if a key is in the cache, without updating the recency of
|
||
|
use. Age is updated if `updateAgeOnHas` is set to `true` in
|
||
|
either the options or the constructor.
|
||
|
|
||
|
Will return `false` if the item is stale, even though it is
|
||
|
technically in the cache.
|
||
|
|
||
|
### `delete(key)`
|
||
|
|
||
|
Deletes a key out of the cache.
|
||
|
|
||
|
Returns `true` if the key was deleted, `false` otherwise.
|
||
|
|
||
|
### `clear()`
|
||
|
|
||
|
Clear the cache entirely, throwing away all values.
|
||
|
|
||
|
Deprecated alias: `reset()`
|
||
|
|
||
|
### `keys()`
|
||
|
|
||
|
Return a generator yielding the keys in the cache, in order from
|
||
|
most recently used to least recently used.
|
||
|
|
||
|
### `rkeys()`
|
||
|
|
||
|
Return a generator yielding the keys in the cache, in order from
|
||
|
least recently used to most recently used.
|
||
|
|
||
|
### `values()`
|
||
|
|
||
|
Return a generator yielding the values in the cache, in order
|
||
|
from most recently used to least recently used.
|
||
|
|
||
|
### `rvalues()`
|
||
|
|
||
|
Return a generator yielding the values in the cache, in order
|
||
|
from least recently used to most recently used.
|
||
|
|
||
|
### `entries()`
|
||
|
|
||
|
Return a generator yielding `[key, value]` pairs, in order from
|
||
|
most recently used to least recently used.
|
||
|
|
||
|
### `rentries()`
|
||
|
|
||
|
Return a generator yielding `[key, value]` pairs, in order from
|
||
|
least recently used to most recently used.
|
||
|
|
||
|
### `find(fn, [getOptions])`
|
||
|
|
||
|
Find a value for which the supplied `fn` method returns a truthy
|
||
|
value, similar to `Array.find()`.
|
||
|
|
||
|
`fn` is called as `fn(value, key, cache)`.
|
||
|
|
||
|
The optional `getOptions` are applied to the resulting `get()` of
|
||
|
the item found.
|
||
|
|
||
|
### `dump()`
|
||
|
|
||
|
Return an array of `[key, entry]` objects which can be passed to
|
||
|
`cache.load()`
|
||
|
|
||
|
The `start` fields are calculated relative to a portable
|
||
|
`Date.now()` timestamp, even if `performance.now()` is available.
|
||
|
|
||
|
Stale entries are always included in the `dump`, even if
|
||
|
`allowStale` is false.
|
||
|
|
||
|
Note: this returns an actual array, not a generator, so it can be
|
||
|
more easily passed around.
|
||
|
|
||
|
### `load(entries)`
|
||
|
|
||
|
Reset the cache and load in the items in `entries` in the order
|
||
|
listed. Note that the shape of the resulting cache may be
|
||
|
different if the same options are not used in both caches.
|
||
|
|
||
|
The `start` fields are assumed to be calculated relative to a
|
||
|
portable `Date.now()` timestamp, even if `performance.now()` is
|
||
|
available.
|
||
|
|
||
|
### `purgeStale()`
|
||
|
|
||
|
Delete any stale entries. Returns `true` if anything was
|
||
|
removed, `false` otherwise.
|
||
|
|
||
|
Deprecated alias: `prune`
|
||
|
|
||
|
### `getRemainingTTL(key)`
|
||
|
|
||
|
Return the number of ms left in the item's TTL. If item is not
|
||
|
in cache, returns `0`. Returns `Infinity` if item is in cache
|
||
|
without a defined TTL.
|
||
|
|
||
|
### `forEach(fn, [thisp])`
|
||
|
|
||
|
Call the `fn` function with each set of `fn(value, key, cache)`
|
||
|
in the LRU cache, from most recent to least recently used.
|
||
|
|
||
|
Does not affect recency of use.
|
||
|
|
||
|
If `thisp` is provided, function will be called in the
|
||
|
`this`-context of the provided object.
|
||
|
|
||
|
### `rforEach(fn, [thisp])`
|
||
|
|
||
|
Same as `cache.forEach(fn, thisp)`, but in order from least
|
||
|
recently used to most recently used.
|
||
|
|
||
|
### `pop()`
|
||
|
|
||
|
Evict the least recently used item, returning its value.
|
||
|
|
||
|
Returns `undefined` if cache is empty.
|
||
|
|
||
|
### Internal Methods and Properties
|
||
|
|
||
|
In order to optimize performance as much as possible, "private"
|
||
|
members and methods are exposed on the object as normal
|
||
|
properties, rather than being accessed via Symbols, private
|
||
|
members, or closure variables.
|
||
|
|
||
|
**Do not use or rely on these.** They will change or be removed
|
||
|
without notice. They will cause undefined behavior if used
|
||
|
inappropriately. There is no need or reason to ever call them
|
||
|
directly.
|
||
|
|
||
|
This documentation is here so that it is especially clear that
|
||
|
this not "undocumented" because someone forgot; it _is_
|
||
|
documented, and the documentation is telling you not to do it.
|
||
|
|
||
|
**Do not report bugs that stem from using these properties.**
|
||
|
They will be ignored.
|
||
|
|
||
|
* `initializeTTLTracking()` Set up the cache for tracking TTLs
|
||
|
* `updateItemAge(index)` Called when an item age is updated, by
|
||
|
internal ID
|
||
|
* `setItemTTL(index)` Called when an item ttl is updated, by
|
||
|
internal ID
|
||
|
* `isStale(index)` Called to check an item's staleness, by
|
||
|
internal ID
|
||
|
* `initializeSizeTracking()` Set up the cache for tracking item
|
||
|
size. Called automatically when a size is specified.
|
||
|
* `removeItemSize(index)` Updates the internal size calculation
|
||
|
when an item is removed or modified, by internal ID
|
||
|
* `addItemSize(index)` Updates the internal size calculation when
|
||
|
an item is added or modified, by internal ID
|
||
|
* `indexes()` An iterator over the non-stale internal IDs, from
|
||
|
most recently to least recently used.
|
||
|
* `rindexes()` An iterator over the non-stale internal IDs, from
|
||
|
least recently to most recently used.
|
||
|
* `newIndex()` Create a new internal ID, either reusing a deleted
|
||
|
ID, evicting the least recently used ID, or walking to the end
|
||
|
of the allotted space.
|
||
|
* `evict()` Evict the least recently used internal ID, returning
|
||
|
its ID. Does not do any bounds checking.
|
||
|
* `connect(p, n)` Connect the `p` and `n` internal IDs in the
|
||
|
linked list.
|
||
|
* `moveToTail(index)` Move the specified internal ID to the most
|
||
|
recently used position.
|
||
|
* `keyMap` Map of keys to internal IDs
|
||
|
* `keyList` List of keys by internal ID
|
||
|
* `valList` List of values by internal ID
|
||
|
* `sizes` List of calculated sizes by internal ID
|
||
|
* `ttls` List of TTL values by internal ID
|
||
|
* `starts` List of start time values by internal ID
|
||
|
* `next` Array of "next" pointers by internal ID
|
||
|
* `prev` Array of "previous" pointers by internal ID
|
||
|
* `head` Internal ID of least recently used item
|
||
|
* `tail` Internal ID of most recently used item
|
||
|
* `free` Stack of deleted internal IDs
|
||
|
|
||
|
## Storage Bounds Safety
|
||
|
|
||
|
This implementation aims to be as flexible as possible, within
|
||
|
the limits of safe memory consumption and optimal performance.
|
||
|
|
||
|
At initial object creation, storage is allocated for `max` items.
|
||
|
If `max` is set to zero, then some performance is lost, and item
|
||
|
count is unbounded. Either `maxSize` or `ttl` _must_ be set if
|
||
|
`max` is not specified.
|
||
|
|
||
|
If `maxSize` is set, then this creates a safe limit on the
|
||
|
maximum storage consumed, but without the performance benefits of
|
||
|
pre-allocation. When `maxSize` is set, every item _must_ provide
|
||
|
a size, either via the `sizeCalculation` method provided to the
|
||
|
constructor, or via a `size` or `sizeCalculation` option provided
|
||
|
to `cache.set()`. The size of every item _must_ be a positive
|
||
|
integer.
|
||
|
|
||
|
If neither `max` nor `maxSize` are set, then `ttl` tracking must
|
||
|
be enabled. Note that, even when tracking item `ttl`, items are
|
||
|
_not_ preemptively deleted when they become stale, unless
|
||
|
`ttlAutopurge` is enabled. Instead, they are only purged the
|
||
|
next time the key is requested. Thus, if `ttlAutopurge`, `max`,
|
||
|
and `maxSize` are all not set, then the cache will potentially
|
||
|
grow unbounded.
|
||
|
|
||
|
In this case, a warning is printed to standard error. Future
|
||
|
versions may require the use of `ttlAutopurge` if `max` and
|
||
|
`maxSize` are not specified.
|
||
|
|
||
|
If you truly wish to use a cache that is bound _only_ by TTL
|
||
|
expiration, consider using a `Map` object, and calling
|
||
|
`setTimeout` to delete entries when they expire. It will perform
|
||
|
much better than an LRU cache.
|
||
|
|
||
|
Here is an implementation you may use, under the same
|
||
|
[license](./LICENSE) as this package:
|
||
|
|
||
|
```js
|
||
|
// a storage-unbounded ttl cache that is not an lru-cache
|
||
|
const cache = {
|
||
|
data: new Map(),
|
||
|
timers: new Map(),
|
||
|
set: (k, v, ttl) => {
|
||
|
if (cache.timers.has(k)) {
|
||
|
clearTimeout(cache.timers.get(k))
|
||
|
}
|
||
|
cache.timers.set(k, setTimeout(() => cache.delete(k), ttl))
|
||
|
cache.data.set(k, v)
|
||
|
},
|
||
|
get: k => cache.data.get(k),
|
||
|
has: k => cache.data.has(k),
|
||
|
delete: k => {
|
||
|
if (cache.timers.has(k)) {
|
||
|
clearTimeout(cache.timers.get(k))
|
||
|
}
|
||
|
cache.timers.delete(k)
|
||
|
return cache.data.delete(k)
|
||
|
},
|
||
|
clear: () => {
|
||
|
cache.data.clear()
|
||
|
for (const v of cache.timers.values()) {
|
||
|
clearTimeout(v)
|
||
|
}
|
||
|
cache.timers.clear()
|
||
|
}
|
||
|
}
|
||
|
```
|
||
|
|
||
|
If that isn't to your liking, check out
|
||
|
[@isaacs/ttlcache](http://npm.im/@isaacs/ttlcache).
|
||
|
|
||
|
## Performance
|
||
|
|
||
|
As of January 2022, version 7 of this library is one of the most
|
||
|
performant LRU cache implementations in JavaScript.
|
||
|
|
||
|
Benchmarks can be extremely difficult to get right. In
|
||
|
particular, the performance of set/get/delete operations on
|
||
|
objects will vary _wildly_ depending on the type of key used. V8
|
||
|
is highly optimized for objects with keys that are short strings,
|
||
|
especially integer numeric strings. Thus any benchmark which
|
||
|
tests _solely_ using numbers as keys will tend to find that an
|
||
|
object-based approach performs the best.
|
||
|
|
||
|
Note that coercing _anything_ to strings to use as object keys is
|
||
|
unsafe, unless you can be 100% certain that no other type of
|
||
|
value will be used. For example:
|
||
|
|
||
|
```js
|
||
|
const myCache = {}
|
||
|
const set = (k, v) => myCache[k] = v
|
||
|
const get = (k) => myCache[k]
|
||
|
|
||
|
set({}, 'please hang onto this for me')
|
||
|
set('[object Object]', 'oopsie')
|
||
|
```
|
||
|
|
||
|
Also beware of "Just So" stories regarding performance. Garbage
|
||
|
collection of large (especially: deep) object graphs can be
|
||
|
incredibly costly, with several "tipping points" where it
|
||
|
increases exponentially. As a result, putting that off until
|
||
|
later can make it much worse, and less predictable. If a library
|
||
|
performs well, but only in a scenario where the object graph is
|
||
|
kept shallow, then that won't help you if you are using large
|
||
|
objects as keys.
|
||
|
|
||
|
In general, when attempting to use a library to improve
|
||
|
performance (such as a cache like this one), it's best to choose
|
||
|
an option that will perform well in the sorts of scenarios where
|
||
|
you'll actually use it.
|
||
|
|
||
|
This library is optimized for repeated gets and minimizing
|
||
|
eviction time, since that is the expected need of a LRU. Set
|
||
|
operations are somewhat slower on average than a few other
|
||
|
options, in part because of that optimization. It is assumed
|
||
|
that you'll be caching some costly operation, ideally as rarely
|
||
|
as possible, so optimizing set over get would be unwise.
|
||
|
|
||
|
If performance matters to you:
|
||
|
|
||
|
1. If it's at all possible to use small integer values as keys,
|
||
|
and you can guarantee that no other types of values will be
|
||
|
used as keys, then do that, and use a cache such as
|
||
|
[lru-fast](https://npmjs.com/package/lru-fast), or
|
||
|
[mnemonist's
|
||
|
LRUCache](https://yomguithereal.github.io/mnemonist/lru-cache)
|
||
|
which uses an Object as its data store.
|
||
|
2. Failing that, if at all possible, use short non-numeric
|
||
|
strings (ie, less than 256 characters) as your keys, and use
|
||
|
[mnemonist's
|
||
|
LRUCache](https://yomguithereal.github.io/mnemonist/lru-cache).
|
||
|
3. If the types of your keys will be long strings, strings that
|
||
|
look like floats, `null`, objects, or some mix of types, or if
|
||
|
you aren't sure, then this library will work well for you.
|
||
|
4. Do not use a `dispose` function, size tracking, or especially
|
||
|
ttl behavior, unless absolutely needed. These features are
|
||
|
convenient, and necessary in some use cases, and every attempt
|
||
|
has been made to make the performance impact minimal, but it
|
||
|
isn't nothing.
|
||
|
|
||
|
## Breaking Changes in Version 7
|
||
|
|
||
|
This library changed to a different algorithm and internal data
|
||
|
structure in version 7, yielding significantly better
|
||
|
performance, albeit with some subtle changes as a result.
|
||
|
|
||
|
If you were relying on the internals of LRUCache in version 6 or
|
||
|
before, it probably will not work in version 7 and above.
|
||
|
|
||
|
For more info, see the [change log](CHANGELOG.md).
|