README.md
1 # lru cache 2 3 A 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 10 npm install lru-cache --save 11 ``` 12 13 ## Usage: 14 15 ```javascript 16 var 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 24 cache.set("key", "value") 25 cache.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. 30 var someObject = { a: 1 } 31 cache.set(someObject, 'a value') 32 // Object keys are not toString()-ed 33 cache.set('[object Object]', 'a different value') 34 assert.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 37 assert.equal(cache.get({ a: 1 }), undefined) 38 39 cache.reset() // empty the cache 40 ``` 41 42 If you put more stuff in it, then items will fall out. 43 44 If you try to put an oversized thing in it, then it'll fall out right 45 away. 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