levelup-cache

library2.3.0jsnpmunverified

Cache remote data in a LevelUP database with automatic refresh and TTL. Version 2.3.0 is the current stable release. Key features: returns cached value immediately regardless of age, automatically calls the getter periodically to check for new values, emits events when changes are detected, and drops items after a configurable TTL since last access. Unlike level-ttl-cache, this library refreshes values even if the key is not accessed, and emits change events. Breaking change in 2.0.0: switched from sublevel to subleveldown. Maintained by TehShrike, low activity.

storage

npm install levelup-cache

github ↗package ↗homepage ↗

INSTALL

IMPORT

SIG · LEVELUP-CACHE

levelup-cache

storagejavascriptv2.3.0

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.

Cache

✓ import Cache from 'levelup-cache'

✗ const { Cache } = require('levelup-cache')

Default export is the constructor. Use named import only if using named exports (not default).

default

✓ const Cache = require('levelup-cache')

✗ const cache = require('levelup-cache').Cache

CommonJS require returns the constructor function directly.

Cache (TypeScript)

✓ import Cache = require('levelup-cache')

✗ import { Cache } from 'levelup-cache'

TypeScript with esModuleInterop: use default import if enabled, otherwise use import = require.

Basic setup: create LevelUP database, define a getter function, instantiate Cache, get a value, listen for changes, and stop the cache.

const levelup = require('levelup') const leveldown = require('leveldown') const Cache = require('levelup-cache') const db = levelup(leveldown('./cache.db')) const getter = (key, cb) => { // simulate remote fetch setTimeout(() => cb(null, { id: 1, content: 'data' }), 100) } const cache = new Cache(db, getter, { refreshEvery: 10000, checkToSeeIfItemsNeedToBeRefreshedEvery: 5000, ttl: 86400000 }) cache.get('mykey', (err, val) => { console.log('cached value:', val) }) cache.on('change', (key, val, prev) => { console.log('value changed for', key) }) setTimeout(() => cache.stop(), 30000)

Debug

Known issues

breakingVersion 2.0.0 switched from sublevel to subleveldown. Existing caches using sublevel will not be compatible.

fix

Upgrade to 2.x and ensure your database is migrated or recreated with subleveldown.

affects: <2.0.0

deprecatedThe 'change' event may be deprecated in future versions; prefer using the 'changed' event if introduced.

fix

Monitor changelog and migrate to any new event names.

affects: >=2.0.0

gotchaThe getter callback must be called exactly once per invocation, otherwise cache may hang.

fix

Ensure your getter calls cb(err, value) exactly once.

affects: >=1.0.0

gotchaComparison function defaults to strict equality (===) which fails for objects. Provide custom comparison for object values to detect changes.

fix

Pass a comparison function that deep-compares values, e.g., using lodash.isEqual.

affects: >=1.0.0

Errors

Common errors & fixes

Error: db.get is not a function

LevelUP instance not passed correctly; db is not a LevelUP object.

fix

Ensure you create a LevelUP instance with a LevelDOWN backend, e.g., const db = levelup(leveldown('./path'))

TypeError: Cannot read property 'on' of undefined

Cache constructor called without new or not receiving a valid LevelUP instance.

fix

Use new Cache(db, getter, options) or ensure db is a LevelUP instance.

AssertionError [ERR_ASSERTION]: TypeError [ERR_INVALID_ARG_TYPE]: The "db" argument must be an instance of LevelUP

Passing an abstract-leveldown database instead of LevelUP.

fix

Use levelup(dbdown) to wrap your leveldown instance.

Upgrade

Version history

2.3.0latest on npm

Audit

Dependencies

leveluprequiredrequired as the database store

subleveldownrequiredused for sublevel support since version 2.0.0

Agent activity

15 hits · last 30 days

node

Resources

githubhttps://github.com/TehShrike/levelup-cache ↗

packagelevelup-cache ↗

homepagehttps://github.com/TehShrike/levelup-cache#readme ↗