140 lines
3.6 KiB
Markdown
140 lines
3.6 KiB
Markdown
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# quick-lru [](https://travis-ci.org/sindresorhus/quick-lru) [](https://coveralls.io/github/sindresorhus/quick-lru?branch=master)
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> Simple [“Least Recently Used” (LRU) cache](https://en.m.wikipedia.org/wiki/Cache_replacement_policies#Least_Recently_Used_.28LRU.29)
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Useful when you need to cache something and limit memory usage.
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Inspired by the [`hashlru` algorithm](https://github.com/dominictarr/hashlru#algorithm), but instead uses [`Map`](https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Map) to support keys of any type, not just strings, and values can be `undefined`.
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## Install
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```
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$ npm install quick-lru
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```
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## Usage
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```js
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const QuickLRU = require('quick-lru');
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const lru = new QuickLRU({maxSize: 1000});
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lru.set('🦄', '🌈');
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lru.has('🦄');
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//=> true
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lru.get('🦄');
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//=> '🌈'
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```
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## API
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### new QuickLRU(options?)
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Returns a new instance.
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### options
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Type: `object`
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#### maxSize
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*Required*\
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Type: `number`
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The maximum number of items before evicting the least recently used items.
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#### maxAge
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Type: `number`\
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Default: `Infinity`
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The maximum number of milliseconds an item should remain in cache.
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By default maxAge will be Infinity, which means that items will never expire.
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Lazy expiration happens upon the next `write` or `read` call.
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Individual expiration of an item can be specified by the `set(key, value, options)` method.
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#### onEviction
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*Optional*\
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Type: `(key, value) => void`
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Called right before an item is evicted from the cache.
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Useful for side effects or for items like object URLs that need explicit cleanup (`revokeObjectURL`).
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### Instance
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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.
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Both `key` and `value` can be of any type.
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#### .set(key, value, options?)
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Set an item. Returns the instance.
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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.
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#### .get(key)
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Get an item.
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#### .has(key)
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Check if an item exists.
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#### .peek(key)
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Get an item without marking it as recently used.
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#### .delete(key)
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Delete an item.
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Returns `true` if the item is removed or `false` if the item doesn't exist.
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#### .clear()
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Delete all items.
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#### .resize(maxSize)
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Update the `maxSize`, discarding items as necessary. Insertion order is mostly preserved, though this is not a strong guarantee.
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Useful for on-the-fly tuning of cache sizes in live systems.
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#### .keys()
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Iterable for all the keys.
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#### .values()
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Iterable for all the values.
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#### .entriesAscending()
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Iterable for all entries, starting with the oldest (ascending in recency).
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#### .entriesDescending()
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Iterable for all entries, starting with the newest (descending in recency).
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#### .size
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The stored item count.
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---
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<div align="center">
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<b>
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<a href="https://tidelift.com/subscription/pkg/npm-quick-lru?utm_source=npm-quick-lru&utm_medium=referral&utm_campaign=readme">Get professional support for this package with a Tidelift subscription</a>
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</b>
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<br>
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<sub>
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Tidelift helps make open source sustainable for maintainers while giving companies<br>assurances about security, maintenance, and licensing for their dependencies.
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</sub>
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</div>
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