README.md
1# lru cache
2
3A cache object that deletes the least-recently-used items.
4
5[](https://travis-ci.org/isaacs/node-lru-cache) [](https://coveralls.io/github/isaacs/node-lru-cache)
6
7## Installation:
8
9```javascript
10npm install lru-cache --save
11```
12
13## Usage:
14
15```javascript
16var LRU = require("lru-cache")
17 , options = { max: 500
18 , length: function (n, key) { return n * 2 + key.length }
19 , dispose: function (key, n) { n.close() }
20 , maxAge: 1000 * 60 * 60 }
21 , cache = new LRU(options)
22 , otherCache = new LRU(50) // sets just the max size
23
24cache.set("key", "value")
25cache.get("key") // "value"
26
27// non-string keys ARE fully supported
28// but note that it must be THE SAME object, not
29// just a JSON-equivalent object.
30var someObject = { a: 1 }
31cache.set(someObject, 'a value')
32// Object keys are not toString()-ed
33cache.set('[object Object]', 'a different value')
34assert.equal(cache.get(someObject), 'a value')
35// A similar object with same keys/values won't work,
36// because it's a different object identity
37assert.equal(cache.get({ a: 1 }), undefined)
38
39cache.reset() // empty the cache
40```
41
42If you put more stuff in it, then items will fall out.
43
44If you try to put an oversized thing in it, then it'll fall out right
45away.
46
47## Options
48
49* `max` The maximum size of the cache, checked by applying the length
50 function to all values in the cache. Not setting this is kind of
51 silly, since that's the whole purpose of this lib, but it defaults
52 to `Infinity`. Setting it to a non-number or negative number will
53 throw a `TypeError`. Setting it to 0 makes it be `Infinity`.
54* `maxAge` Maximum age in ms. Items are not pro-actively pruned out
55 as they age, but if you try to get an item that is too old, it'll
56 drop it and return undefined instead of giving it to you.
57 Setting this to a negative value will make everything seem old!
58 Setting it to a non-number will throw a `TypeError`.
59* `length` Function that is used to calculate the length of stored
60 items. If you're storing strings or buffers, then you probably want
61 to do something like `function(n, key){return n.length}`. The default is
62 `function(){return 1}`, which is fine if you want to store `max`
63 like-sized things. The item is passed as the first argument, and
64 the key is passed as the second argumnet.
65* `dispose` Function that is called on items when they are dropped
66 from the cache. This can be handy if you want to close file
67 descriptors or do other cleanup tasks when items are no longer
68 accessible. Called with `key, value`. It's called *before*
69 actually removing the item from the internal cache, so if you want
70 to immediately put it back in, you'll have to do that in a
71 `nextTick` or `setTimeout` callback or it won't do anything.
72* `stale` By default, if you set a `maxAge`, it'll only actually pull
73 stale items out of the cache when you `get(key)`. (That is, it's
74 not pre-emptively doing a `setTimeout` or anything.) If you set
75 `stale:true`, it'll return the stale value before deleting it. If
76 you don't set this, then it'll return `undefined` when you try to
77 get a stale entry, as if it had already been deleted.
78* `noDisposeOnSet` By default, if you set a `dispose()` method, then
79 it'll be called whenever a `set()` operation overwrites an existing
80 key. If you set this option, `dispose()` will only be called when a
81 key falls out of the cache, not when it is overwritten.
82* `updateAgeOnGet` When using time-expiring entries with `maxAge`,
83 setting this to `true` will make each item's effective time update
84 to the current time whenever it is retrieved from cache, causing it
85 to not expire. (It can still fall out of cache based on recency of
86 use, of course.)
87
88## API
89
90* `set(key, value, maxAge)`
91* `get(key) => value`
92
93 Both of these will update the "recently used"-ness of the key.
94 They do what you think. `maxAge` is optional and overrides the
95 cache `maxAge` option if provided.
96
97 If the key is not found, `get()` will return `undefined`.
98
99 The key and val can be any value.
100
101* `peek(key)`
102
103 Returns the key value (or `undefined` if not found) without
104 updating the "recently used"-ness of the key.
105
106 (If you find yourself using this a lot, you *might* be using the
107 wrong sort of data structure, but there are some use cases where
108 it's handy.)
109
110* `del(key)`
111
112 Deletes a key out of the cache.
113
114* `reset()`
115
116 Clear the cache entirely, throwing away all values.
117
118* `has(key)`
119
120 Check if a key is in the cache, without updating the recent-ness
121 or deleting it for being stale.
122
123* `forEach(function(value,key,cache), [thisp])`
124
125 Just like `Array.prototype.forEach`. Iterates over all the keys
126 in the cache, in order of recent-ness. (Ie, more recently used
127 items are iterated over first.)
128
129* `rforEach(function(value,key,cache), [thisp])`
130
131 The same as `cache.forEach(...)` but items are iterated over in
132 reverse order. (ie, less recently used items are iterated over
133 first.)
134
135* `keys()`
136
137 Return an array of the keys in the cache.
138
139* `values()`
140
141 Return an array of the values in the cache.
142
143* `length`
144
145 Return total length of objects in cache taking into account
146 `length` options function.
147
148* `itemCount`
149
150 Return total quantity of objects currently in cache. Note, that
151 `stale` (see options) items are returned as part of this item
152 count.
153
154* `dump()`
155
156 Return an array of the cache entries ready for serialization and usage
157 with 'destinationCache.load(arr)`.
158
159* `load(cacheEntriesArray)`
160
161 Loads another cache entries array, obtained with `sourceCache.dump()`,
162 into the cache. The destination cache is reset before loading new entries
163
164* `prune()`
165
166 Manually iterates over the entire cache proactively pruning old entries
167
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