lru cache

A cache object that deletes the least-recently-used items.

Installation:

npm install lru-cache --save

Usage:

var LRU = require("lru-cache")
  , options = { max: 500
              , length: function (n, key) { return n * 2 + key.length }
              , dispose: function (key, n) { n.close() }
              , maxAge: 1000 * 60 * 60 }
  , cache = new LRU(options)
  , otherCache = new LRU(50) // sets just the max size

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.reset()    // empty the cache

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.

Options

• max The maximum size of the cache, checked by applying the length
  function 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. Setting it to a non-number or negative number will
  throw a TypeError. Setting it to 0 makes it be Infinity.
• maxAge Maximum age in ms. Items are not pro-actively pruned out
  as 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.
  Setting this to a negative value will make everything seem old!
  Setting it to a non-number will throw a TypeError.
• length Function that is used to calculate the length of stored
  items. If you're storing strings or buffers, then you probably want
  to do something like function(n, key){return n.length}. The default is
  function(){return 1}, which is fine if you want to store max
  like-sized things. The item is passed as the first argument, and
  the key is passed as the second argumnet.
• dispose Function that is called on items when they are dropped
  from 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 before
  actually 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 or setTimeout callback or it won't do anything.
• stale By default, if you set a maxAge, it'll only actually pull
  stale items out of the cache when you get(key). (That is, it's
  not pre-emptively doing a setTimeout or anything.) If you set
  stale:true, it'll return the stale value before deleting it. If
  you don't set this, then it'll return undefined when you try to
  get a stale entry, as if it had already been deleted.
• noDisposeOnSet By default, if you set a dispose() method, then
  it'll be called whenever a set() operation overwrites an existing
  key. If you set this option, dispose() will only be called when a
  key falls out of the cache, not when it is overwritten.
• updateAgeOnGet When using time-expiring entries with maxAge,
  setting this to true will make each item's effective time update
  to the current time whenever it is retrieved from cache, causing it
  to not expire. (It can still fall out of cache based on recency of
  use, of course.)

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. maxAge is optional and overrides the
  cache maxAge option if provided.

  If the key is not found, get() will return undefined.

  The key and val can be any value.

• 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.)

• rforEach(function(value,key,cache), [thisp])

  The same as cache.forEach(...) but items are iterated over in
  reverse order. (ie, less 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

• prune()

  Manually iterates over the entire cache proactively pruning old entries