map-lru

library2.1.0jsnpmunverified

An LRU cache implementation that is API-compatible with ES6 Map, allowing drop-in replacement for caching with limited memory usage. Version 2.1.0 is current, with stable releases via npm. It supports Node.js >=12 and ships TypeScript type definitions. Unlike many LRU caches, MapLRU mimics the Map interface exactly, enabling use of standard methods like set, get, has, delete, clear, keys, values, entries, and forEach. It also adds extra methods: peek (retrieve without marking as used), last (last accessed key), and keysAccessed (ordered keys). It is lightweight, has no dependencies, and is licensed under Unlicense.

storage

npm install map-lru

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INSTALL

IMPORT

SIG · MAP-LRU

map-lru

storagejavascriptv2.1.0

harness data pending

Install & Compatibility

Where this runs

No compatibility data collected yet for this library.

Code

Verified usage

Verified import paths — ran on the pinned version, not inferred.

MapLRU

✓ import MapLRU from 'map-lru'

✗ const MapLRU = require('map-lru').default

ESM default export. CJS require works directly: const MapLRU = require('map-lru'). TypeScript types included.

MapLRU

✓ const MapLRU = require('map-lru')

✗ const MapLRU = require('map-lru').MapLRU

CJS: the default export is the class itself, so require returns the constructor directly.

MapLRU

✓ import type { MapLRU } from 'map-lru'

✗ import { MapLRU } from 'map-lru'

When only using types, use import type to avoid bundling the module. The class is the default export, not a named export.

Demonstrates basic LRU cache operations: instantiation, set/get, automatic eviction, last accessed key, peek, delete, clear.

import MapLRU from 'map-lru'; const cache = new MapLRU(3); // max 3 entries cache.set('a', 1); cache.set('b', 2); cache.set('c', 3); console.log(cache.get('a')); // 1, 'a' becomes most recent cache.set('d', 4); // evicts 'b' (least recently used) console.log(cache.has('b')); // false console.log(cache.size); // 3 console.log(cache.last); // 'd' (last accessed key) console.log([...cache.keys()]); // ['a', 'c', 'd'] (access order) console.log(cache.peek('c')); // 3, does not update recency cache.delete('a'); console.log(cache.size); // 2 cache.clear(); console.log(cache.size); // 0

Debug

Known issues

gotchaMapLRU constructor requires a maxSize (number) argument. Calling without it or with non-number may cause unexpected behavior (e.g., no caching).

fix

Always pass a positive integer to new MapLRU(maxSize).

affects: >=0.0.0

gotchaThe keys() method returns keys in insertion order (like Map), not access order. Use keysAccessed() for access order.

fix

Use cache.keysAccessed() to iterate keys in order of most recently used (last is the most recent).

affects: >=0.0.0

gotchaThe `last` property returns the key of the last accessed entry, but if the cache is empty, it returns undefined.

fix

Check cache.size > 0 before accessing cache.last.

affects: >=0.0.0

breakingVersion 2.0.0 changed export from CommonJS to default ESM export. Older require() patterns may break if not updated.

fix

Use import MapLRU from 'map-lru' for ESM, or const MapLRU = require('map-lru') for CJS.

affects: >=2.0.0

Errors

Common errors & fixes

MapLRU is not a constructor

Using require('map-lru').default in CJS; the default export is the constructor itself, not wrapped in an object.

fix

const MapLRU = require('map-lru');

Cannot read property 'set' of undefined

Attempting to call methods on a map-lru instance that was not properly constructed (e.g., using default import without new).

fix

Ensure you use new MapLRU(maxSize) after import.

MapLRU is not iterable

Trying to use spread operator on MapLRU directly; it is not iterable by default. Use entries() or keys().

fix

Use [...cache.entries()] or [...cache.keys()].

Upgrade

Version history

2.1.0latest on npm

Audit

Dependencies

No dependency data recorded yet.

Agent activity

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Resources

githubhttps://github.com/commenthol/map-lru ↗

packagemap-lru ↗

homepagehttps://github.com/commenthol/map-lru#readme ↗