# quick-lru [](https://codecov.io/gh/sindresorhus/quick-lru/branch/main)
> Simple [“Least Recently Used” (LRU) cache](https://en.m.wikipedia.org/wiki/Cache_replacement_policies#Least_Recently_Used_.28LRU.29)
Useful when you need to cache something and limit memory usage.
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`.
## Install
```
$ npm install quick-lru
```
## Usage
```js
import QuickLRU from 'quick-lru';
const lru = new QuickLRU({maxSize: 1000});
lru.set('🦄', '🌈');
lru.has('🦄');
//=> true
lru.get('🦄');
//=> '🌈'
```
## API
### new QuickLRU(options?)
Returns a new instance.
It's a [`Map`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map) subclass.
### options
Type: `object`
#### maxSize
*Required*\
Type: `number`
The maximum number of items before evicting the least recently used items.
#### 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.
Useful for side effects or for items like object URLs that need explicit cleanup (`revokeObjectURL`).
### Instance
The instance is an [`Iterable`](https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Iteration_protocols) of `[key, value]` pairs 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.
#### .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).
#### .entries()
Iterable for all entries, starting with the newest (ascending in recency).
**This method exists for `Map` compatibility. Prefer [.entriesAscending()](#entriesascending) instead.**
#### .forEach(callbackFunction, thisArgument)
Loop over entries calling the `callbackFunction` for each entry (ascending in recency).
**This method exists for `Map` compatibility. Prefer [.entriesAscending()](#entriesascending) instead.**
#### .size
The stored item count.
## Related
- [yocto-queue](https://github.com/sindresorhus/yocto-queue) - Tiny queue data structure
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