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An extendable JSON database for Node and the browser powered by lodash
Filed under dataShow Alllowdb
Simple to use type-safe local JSON database 🦉
If you know JavaScript, you know how to use lowdb.
Read or create
db.json
const db = await JSONFilePreset('db.json', { posts: [] })
Use plain JavaScript to change data
const post = { id: 1, title: 'lowdb is awesome', views: 100 } // In two steps db.data.posts.push(post) await db.write() // Or in one await db.update(({ posts }) => posts.push(post))
// db.json { "posts": [ { "id": 1, "title": "lowdb is awesome", "views": 100 } ] }
In the same spirit, query using native
Array
functions:const { posts } = db.data posts.at(0) // First post posts.filter((post) => post.title.includes('lowdb')) // Filter by title posts.find((post) => post.id === 1) // Find by id posts.toSorted((a, b) => a.views - b.views) // Sort by views
It's that simple.
db.data
is just a JavaScript object, no magic.Sponsors
Become a sponsor and have your company logo here 👉 GitHub Sponsors
Features
- Lightweight
- Minimalist
- TypeScript
- Plain JavaScript
- Safe atomic writes
- Hackable:
- Change storage, file format (JSON, YAML, ...) or add encryption via adapters
- Extend it with lodash, ramda, ... for super powers!
- Automatically switches to fast in-memory mode during tests
Install
npm install lowdb
Usage
Lowdb is a pure ESM package. If you're having trouble using it in your project, please read this.
import { JSONFilePreset } from 'lowdb/node' // Read or create db.json const defaultData = { posts: [] } const db = await JSONFilePreset('db.json', defaultData) // Update db.json await db.update(({ posts }) => posts.push('hello world')) // Alternatively you can call db.write() explicitely later // to write to db.json db.data.posts.push('hello world') await db.write()
// db.json { "posts": [ "hello world" ] }
TypeScript
You can use TypeScript to check your data types.
type Data = { messages: string[] } const defaultData: Data = { messages: [] } const db = await JSONPreset<Data>('db.json', defaultData) db.data.messages.push('foo') // ✅ Success db.data.messages.push(1) // ❌ TypeScript error
Lodash
You can extend lowdb with Lodash (or other libraries). To be able to extend it, we're not using
JSONPreset
here. Instead, we're using lower components.import { Low } from 'lowdb' import { JSONFile } from 'lowdb/node' import lodash from 'lodash' type Post = { id: number title: string } type Data = { posts: Post[] } // Extend Low class with a new `chain` field class LowWithLodash<T> extends Low<T> { chain: lodash.ExpChain<this['data']> = lodash.chain(this).get('data') } const defaultData: Data = { posts: [], } const adapter = new JSONFile<Data>('db.json', defaultData) const db = new LowWithLodash(adapter) await db.read() // Instead of db.data use db.chain to access lodash API const post = db.chain.get('posts').find({ id: 1 }).value() // Important: value() must be called to execute chain
CLI, Server, Browser and in tests usage
See
src/examples/
directory.API
Presets
Lowdb provides four presets for common cases.
JSONFilePreset(filename, defaultData)
JSONFileSyncPreset(filename, defaultData)
LocalStoragePreset(name, defaultData)
SessionStoragePreset(name, defaultData)
See
src/examples/
directory for usage.Lowdb is extremely flexible, if you need to extend it or modify its behavior, use the classes and adapters below instead of the presets.
Classes
Lowdb has two classes (for asynchronous and synchronous adapters).
new Low(adapter, defaultData)
import { Low } from 'lowdb' import { JSONFile } from 'lowdb/node' const db = new Low(new JSONFile('file.json'), {}) await db.read() await db.write()
new LowSync(adapterSync, defaultData)
import { LowSync } from 'lowdb' import { JSONFileSync } from 'lowdb/node' const db = new LowSync(new JSONFileSync('file.json'), {}) db.read() db.write()
Methods
db.read()
Calls
adapter.read()
and setsdb.data
.Note:
JSONFile
andJSONFileSync
adapters will setdb.data
tonull
if file doesn't exist.db.data // === null db.read() db.data // !== null
db.write()
Calls
adapter.write(db.data)
.db.data = { posts: [] } db.write() // file.json will be { posts: [] } db.data = {} db.write() // file.json will be {}
db.update(fn)
Calls
fn()
thendb.write()
.db.update((data) => { // make changes to data // ... }) // files.json will be updated
Properties
db.data
Holds your db content. If you're using the adapters coming with lowdb, it can be any type supported by
JSON.stringify
.For example:
db.data = 'string' db.data = [1, 2, 3] db.data = { key: 'value' }
Adapters
Lowdb adapters
JSONFile
JSONFileSync
Adapters for reading and writing JSON files.
import { JSONFile, JSONFileSync } from 'lowdb/node' new Low(new JSONFile(filename), {}) new LowSync(new JSONFileSync(filename), {})
Memory
MemorySync
In-memory adapters. Useful for speeding up unit tests. See
src/examples/
directory.import { Memory, MemorySync } from 'lowdb' new Low(new Memory(), {}) new LowSync(new MemorySync(), {})
LocalStorage
SessionStorage
Synchronous adapter for
window.localStorage
andwindow.sessionStorage
.import { LocalStorage, SessionStorage } from 'lowdb/browser' new LowSync(new LocalStorage(name), {}) new LowSync(new SessionStorage(name), {})
Utility adapters
TextFile
TextFileSync
Adapters for reading and writing text. Useful for creating custom adapters.
DataFile
DataFileSync
Adapters for easily supporting other data formats or adding behaviors (encrypt, compress...).
import { DataFile } from 'lowdb' new DataFile(filename, { parse: YAML.parse, stringify: YAML.stringify }) new DataFile(filename, { parse: (data) => { decypt(JSON.parse(data)) }, stringify: (str) => { encrypt(JSON.stringify(str)) } })
Third-party adapters
If you've published an adapter for lowdb, feel free to create a PR to add it here.
Writing your own adapter
You may want to create an adapter to write
db.data
to YAML, XML, encrypt data, a remote storage, ...An adapter is a simple class that just needs to expose two methods:
class AsyncAdapter { read() { /* ... */ } // should return Promise<data> write(data) { /* ... */ } // should return Promise<void> } class SyncAdapter { read() { /* ... */ } // should return data write(data) { /* ... */ } // should return nothing }
For example, let's say you have some async storage and want to create an adapter for it:
import { api } from './AsyncStorage' class CustomAsyncAdapter { // Optional: your adapter can take arguments constructor(args) { // ... } async read() { const data = await api.read() return data } async write(data) { await api.write(data) } } const adapter = new CustomAsyncAdapter() const db = new Low(adapter)
See
src/adapters/
for more examples.Custom serialization
To create an adapter for another format than JSON, you can use
TextFile
orTextFileSync
.For example:
import { Adapter, Low } from 'lowdb' import { TextFile } from 'lowdb/node' import YAML from 'yaml' class YAMLFile { constructor(filename) { this.adapter = new TextFile(filename) } async read() { const data = await this.adapter.read() if (data === null) { return null } else { return YAML.parse(data) } } write(obj) { return this.adapter.write(YAML.stringify(obj)) } } const adapter = new YAMLFile('file.yaml') const db = new Low(adapter)
Limits
Lowdb doesn't support Node's cluster module.
If you have large JavaScript objects (
~10-100MB
) you may hit some performance issues. This is because whenever you calldb.write
, the wholedb.data
is serialized usingJSON.stringify
and written to storage.Depending on your use case, this can be fine or not. It can be mitigated by doing batch operations and calling
db.write
only when you need it.If you plan to scale, it's highly recommended to use databases like PostgreSQL or MongoDB instead.