quick-lru

Simple “Least Recently Used” (LRU) cache

Useful when you need to cache something and limit memory usage.

Inspired by the hashlru algorithm, but instead uses Map to support keys of any type, not just strings, and values can be undefined.

Install

npm install quick-lru

Usage

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 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 the cache. By default, maxAge will be Infinity, which means that items will never expire.

Lazy expiration occurs 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 of [key, value] pairs so you can use it directly in a 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 in 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.

.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’s expired.
• Returns Infinity if the item has no expiration (maxAge not set for the item and no global maxAge).
• May return a negative number if the item has already expired but has not yet been lazily removed.

.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 oldest (ascending in recency).

This method exists for Map compatibility. Prefer .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() instead.

.size (getter)

The stored item count.

.maxSize (getter)

The set max size.

Related

• yocto-queue - Tiny queue data structure