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| # @alloc/quick-lru [](https://travis-ci.org/aleclarson/quick-lru) [](https://coveralls.io/github/aleclarson/quick-lru?branch=master) | |
| > Simple [“Least Recently Used” (LRU) cache](https://en.m.wikipedia.org/wiki/Cache_replacement_policies#Least_Recently_Used_.28LRU.29) | |
| This is a CommonJS-only fork of [`quick-lru`](https://github.com/sindresorhus/quick-lru). | |
| Useful when you need to cache something and limit memory usage. | |
| See the [algorithm section](#algorithm) for implementation details. | |
| ## Install | |
| ``` | |
| $ npm install @alloc/quick-lru | |
| ``` | |
| ## Usage | |
| ```js | |
| const QuickLRU = require('@alloc/quick-lru'); | |
| const lru = new QuickLRU({maxSize: 1000}); | |
| lru.set('🦄', '🌈'); | |
| lru.has('🦄'); | |
| //=> true | |
| lru.get('🦄'); | |
| //=> '🌈' | |
| ``` | |
| ## API | |
| ### new QuickLRU(options?) | |
| Returns a new instance. | |
| ### options | |
| Type: `object` | |
| #### maxSize | |
| *Required*\ | |
| Type: `number` | |
| The target maximum number of items before evicting the least recently used items. | |
| > **Note:** The dual-cache algorithm may physically retain up to twice `maxSize` entries for performance reasons, even though the reported cache size does not exceed `maxSize`. | |
| #### maxAge | |
| Type: `number`\ | |
| Default: `Infinity` | |
| The maximum number of milliseconds an item should remain in cache. | |
| By default maxAge will be Infinity, which means that items will never expire. | |
| Lazy expiration happens upon the next `write` or `read` call. | |
| Individual expiration of an item can be specified by the `set(key, value, options)` method. | |
| #### onEviction | |
| *Optional*\ | |
| Type: `(key, value) => void` | |
| Called right before an item is evicted from the cache due to capacity pressure or TTL expiration. | |
| Useful for side effects or for items like object URLs that need explicit cleanup (`revokeObjectURL`). | |
| This callback is not called for manual removals via `delete()` or `clear()`. | |
| ### Instance | |
| The instance is [`iterable`](https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Iteration_protocols) so you can use it directly in a [`for…of`](https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Statements/for...of) loop. | |
| Both `key` and `value` can be of any type. | |
| #### .set(key, value, options?) | |
| Set an item. Returns the instance. | |
| Individual expiration of an item can be specified with the `maxAge` option. If not specified, the global `maxAge` value will be used in case it is specified on the constructor, otherwise the item will never expire. | |
| #### .get(key) | |
| Get an item. | |
| #### .has(key) | |
| Check if an item exists. | |
| #### .peek(key) | |
| Get an item without marking it as recently used. | |
| #### .expiresIn(key) | |
| Get the remaining time to live (in milliseconds) for the given item, or `undefined` if the item is not in the cache. | |
| - Does not mark the item as recently used. | |
| - Does not trigger lazy expiration or remove the entry when it is expired. | |
| - Returns `Infinity` if the item has no expiration. | |
| - May return a negative number if the item has already expired but has not yet been lazily removed. | |
| #### .delete(key) | |
| Delete an item. | |
| Returns `true` if the item is removed or `false` if the item doesn't exist. | |
| #### .clear() | |
| Delete all items. | |
| #### .resize(maxSize) | |
| Update the `maxSize`, discarding items as necessary. Insertion order is mostly preserved, though this is not a strong guarantee. | |
| Useful for on-the-fly tuning of cache sizes in live systems. | |
| #### .keys() | |
| Iterable for all the keys. | |
| #### .values() | |
| Iterable for all the values. | |
| #### .entriesAscending() | |
| Iterable for all entries, starting with the oldest (ascending in recency). | |
| #### .entriesDescending() | |
| Iterable for all entries, starting with the newest (descending in recency). | |
| #### .size | |
| The stored item count. | |
| ## Algorithm | |
| This library implements a variant of the [`hashlru` algorithm](https://github.com/dominictarr/hashlru#algorithm) using two [`Map`](https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Map) objects. One map holds recently added or accessed entries, while the other holds older entries. When the recent map reaches `maxSize`, it replaces the older map and a new recent map is created. | |
| This avoids the frequent delete operations required by a traditional linked-list LRU and supports keys of any type and `undefined` values. The tradeoff is that the two maps may physically retain up to twice the target `maxSize` between rotations. Use a strict-size cache when that temporary memory overhead is unacceptable. | |
| --- | |
| <div align="center"> | |
| <b> | |
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| </b> | |
| <br> | |
| <sub> | |
| Tidelift helps make open source sustainable for maintainers while giving companies<br>assurances about security, maintenance, and licensing for their dependencies. | |
| </sub> | |
| </div> | |