lru cache
A cache object that deletes the least-recently-used items.
Usage:
If you put more stuff in it, then items will fall out.
If you try to put an oversized thing in it, then it'll fall out right away.
Keys should always be Strings or Numbers
Note: this module will print warnings to console.error
if you use a key that is not a String or Number. Because items are stored in an object, which coerces keys to a string, it won't go well for you if you try to use a key that is not a unique string, it'll cause surprise collisions. For example:
Options
max
The maximum size of the cache, checked by applying the lengthfunction to all values in the cache. Not setting this is kind of
silly, since that's the whole purpose of this lib, but it defaults
to
Infinity
.maxAge
Maximum age in ms. Items are not pro-actively pruned outas they age, but if you try to get an item that is too old, it'll
drop it and return undefined instead of giving it to you.
length
Function that is used to calculate the length of storeditems. If you're storing strings or buffers, then you probably want
to do something like
function(n){return n.length}
. The default isfunction(n){return 1}
, which is fine if you want to storemax
like-sized things.
dispose
Function that is called on items when they are droppedfrom the cache. This can be handy if you want to close file
descriptors or do other cleanup tasks when items are no longer
accessible. Called with
key, value
. It's called beforeactually removing the item from the internal cache, so if you want
to immediately put it back in, you'll have to do that in a
nextTick
orsetTimeout
callback or it won't do anything.stale
By default, if you set amaxAge
, it'll only actually pullstale items out of the cache when you
get(key)
. (That is, it'snot pre-emptively doing a
setTimeout
or anything.) If you setstale:true
, it'll return the stale value before deleting it. Ifyou don't set this, then it'll return
undefined
when you try toget a stale entry, as if it had already been deleted.
API
set(key, value, maxAge)
get(key) => value
Both of these will update the "recently used"-ness of the key. They do what you think.
max
is optional and overrides the cachemax
option if provided.peek(key)
Returns the key value (or
undefined
if not found) without updating the "recently used"-ness of the key.(If you find yourself using this a lot, you might be using the wrong sort of data structure, but there are some use cases where it's handy.)
del(key)
Deletes a key out of the cache.
reset()
Clear the cache entirely, throwing away all values.
has(key)
Check if a key is in the cache, without updating the recent-ness or deleting it for being stale.
forEach(function(value,key,cache), [thisp])
Just like
Array.prototype.forEach
. Iterates over all the keys in the cache, in order of recent-ness. (Ie, more recently used items are iterated over first.)keys()
Return an array of the keys in the cache.
values()
Return an array of the values in the cache.
length()
Return total length of objects in cache taking into account
length
options function.itemCount
Return total quantity of objects currently in cache. Note, that
stale
(see options) items are returned as part of this item count.dump()
Return an array of the cache entries ready for serialization and usage with 'destinationCache.load(arr)`.
load(cacheEntriesArray)
Loads another cache entries array, obtained with
sourceCache.dump()
, into the cache. The destination cache is reset before loading new entries
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