# lowdb [![](http://img.shields.io/npm/dm/lowdb.svg?style=flat)](https://www.npmjs.org/package/lowdb) [![Node.js CI](https://github.com/typicode/lowdb/actions/workflows/node.js.yml/badge.svg)](https://github.com/typicode/lowdb/actions/workflows/node.js.yml) > Simple to use type-safe local JSON database 🦉 Read or create `db.json` ```js const db = await JSONFilePreset('db.json', { posts: [] }) ``` Update data using `Array.prototype.*` and automatically write to `db.json` ```js const post = { id: 1, title: 'lowdb is awesome', views: 100 } await db.update(({ posts }) => posts.push(post)) ``` ```js // db.json { "posts": [ { "id": 1, "title": "lowdb is awesome", "views": 100 } ] } ``` In the same spirit, query using native `Array.prototype.*` ```js const { posts } = db.data const first = posts.at(0) const results = posts.filter((post) => post.title.includes('lowdb')) const post1 = posts.find((post) => post.id === 1) const sortedPosts = posts.toSorted((a, b) => a.views - b.views) ``` It's that simple. ## Sponsors

[Become a sponsor and have your company logo here](https://github.com/sponsors/typicode) 👉 [GitHub Sponsors](https://github.com/sponsors/typicode) ## Features - **Lightweight** - **Minimalist** - **TypeScript** - **Plain JavaScript** - Safe atomic writes - Hackable: - Change storage, file format (JSON, YAML, ...) or add encryption via [adapters](#adapters) - Extend it with lodash, ramda, ... for super powers! - Automatically switches to fast in-memory mode during tests ## Install ```sh npm install lowdb ``` ## Usage _Lowdb is a pure ESM package. If you're having trouble using it in your project, please [read this](https://gist.github.com/sindresorhus/a39789f98801d908bbc7ff3ecc99d99c)._ ```js 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() ``` ```js // db.json { "posts": [ "hello world" ] } ``` ### TypeScript You can use TypeScript to check your data types. ```ts type Data = { messages: string[] } const defaultData: Data = { messages: [] } const db = await JSONPreset('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. ```ts 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 extends Low { chain: lodash.ExpChain = lodash.chain(this).get('data') } const defaultData: Data = { posts: [], } const adapter = new JSONFile('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/`](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/`](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)` ```js 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)` ```js 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 sets `db.data`. **Note:** `JSONFile` and `JSONFileSync` adapters will set `db.data` to `null` if file doesn't exist. ```js db.data // === null db.read() db.data // !== null ``` #### `db.write()` Calls `adapter.write(db.data)`. ```js db.data = { posts: [] } db.write() // file.json will be { posts: [] } db.data = {} db.write() // file.json will be {} ``` #### `db.update(fn)` Calls `fn()` then `db.write()`. ```js 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`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify). For example: ```js db.data = 'string' db.data = [1, 2, 3] db.data = { key: 'value' } ``` ## Adapters ### Lowdb adapters #### `JSONFile` `JSONFileSync` Adapters for reading and writing JSON files. ```js 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/`](src/examples) directory. ```js import { Memory, MemorySync } from 'lowdb' new Low(new Memory(), {}) new LowSync(new MemorySync(), {}) ``` #### `LocalStorage` `SessionStorage` Synchronous adapter for `window.localStorage` and `window.sessionStorage`. ```js 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...). ```js 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: ```js class AsyncAdapter { read() { /* ... */ } // should return Promise write(data) { /* ... */ } // should return Promise } 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: ```js 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/`](src/adapters) for more examples. #### Custom serialization To create an adapter for another format than JSON, you can use `TextFile` or `TextFileSync`. For example: ```js 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 call `db.write`, the whole `db.data` is serialized using `JSON.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.

	Stars	Issues	Version	Updated	Created
forerunner	6	3	0.3.17	10 years ago	11 years ago
lokijs	6,731	31	1.5.12	3 years ago	11 years ago
lowdb	21,354	4	7.0.1	9 months ago	10 years ago
pouchdb	16,740	141	9.0.0	3 months ago	12 years ago
realm	5,740	612	12.13.1	a month ago	12 years ago
taffydb	2,213	111	2.7.3	8 years ago	13 years ago

forerunner vs lokijs vs lowdb vs pouchdb vs realm vs taffydb

Downloads in past1 Month3 Months6 Months1 Year2 Years5 YearsAll time

Stats

Sick of boring JavaScript newsletters?

Downloads in past