# 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
jsonplaceholder	4,982	85	0.3.3	8 years ago	11 years ago
lowdb	20,967	0	7.0.1	5 months ago	10 years ago
mock-server	56	7	1.3.3	10 years ago	12 years ago
mockaroo	42	4	1.0.1	13 days ago	9 years ago
mocky	26	0	0.1.11	7 years ago	11 years ago

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