Level 10: one key-value database API for Node.js and browsers

Why Level 10 sits above two storage backends

Level addresses a portability problem at the package boundary. An application needs a sorted key-value database in Node.js, while code delivered to a browser needs storage backed by a browser database rather than the Node.js implementation. Level avoids asking application code to import and switch between those implementations directly. According to the README, it exports classic-level in Node.js and browser-level in browsers.

The resulting abstraction is primarily an entry point and shared API surface. It is not itself a new storage engine. Based on package.json, its runtime dependencies are abstract-level, browser-level and classic-level. The package declares index.js as its CommonJS main entry and browser.js as its browser entry. A bundler that honors the browser field can therefore resolve the browser-facing implementation while Node.js resolves the package's main implementation.

This arrangement targets developers who want application code to retain the same basic operations across Node.js and browsers. The common operations include opening a database, storing values, retrieving them, writing batches and iterating over entries in key order. Type declarations describe methods common to classic-level and browser-level rather than presenting every backend-specific method as portable.

That boundary matters when selecting dependencies. Level is convenient when cross-runtime consistency matters more than access to every option of a particular backend. It is not a complete abstraction over database servers, network replication, transactions, relational querying or document models. It is a local database package organized around ordered keys and values.

The path from put and get to ordered iteration

A Level database stores each entry under a key and encodes values according to the configured format. The README's JavaScript example creates a database with JSON value encoding, writes the key a with value 1, adds a second entry in a batch, retrieves a and iterates over keys greater than a. This sequence shows the central data path without introducing a separate schema or query language.

Lexicographic ordering comes from the key order of the underlying LevelDB-style storage. Iteration can be constrained by a bound such as gt, which in the example selects entries after the key a. The returned value for that single qualifying entry is 2. Applications can use this ordered access pattern for prefix scans, bounded scans and sequential processing.

The `put` operation handles one key-value entry. The `batch` operation accepts an array of typed operations and can add multiple entries in one call. The documented example contains one operation, which is enough to demonstrate the shape but does not establish transaction semantics beyond what `abstract-level` documents. The README refers readers to `abstract-level` for the API and to each backend's README for additional options and methods.

Keys and values may be binary as well as text. JSON encoding affects values, not the abstraction itself. For a typed JavaScript application, `index.d.ts` supplies declarations common to both implementations. TypeScript users can specify key and value generics at the database and sublevel levels, while an individual operation can override its encoding. This is useful when the normal database encoding does not match the representation required at one call site.

Installing Level 10 and writing the first database

The README gives npm as the installation path. This command adds the package to the current Node.js project and resolves its declared runtime dependencies.

npm install level

For a first use, create a CommonJS script with the documented constructor and operations. The location `example` is the database directory in Node.js. The `valueEncoding` setting makes the numeric and object-like values JSON values rather than UTF-8 strings.

const { Level } = require('level')

const db = new Level('example', { valueEncoding: 'json' })

await db.put('a', 1)
await db.batch([{ type: 'put', key: 'b', value: 2 }])

const value = await db.get('a')

for await (const [key, value] of db.iterator({ gt: 'a' })) {
  console.log(value)
}

This example requires top-level `await`, so the script must be run in a module context that supports it. The README presents the example as JavaScript, while package.json declares `index.js` as the main entry; the repository excerpt does not provide a dedicated first-script command. Readers should consult their project's module settings rather than inventing a runner command.

The expected behavior stated by the example is that `get('a')` produces 1. Iteration over keys greater than `a` yields the entry for `b`, whose logged value is 2. Browser applications need a bundler such as Browserify, webpack or Rollup. The README links starter projects for Browserify and webpack rather than providing a complete browser setup in this repository.

Node.js, browser and TypeScript deployment constraints

The declared runtime floor is Node.js 18 or newer. The README also states support for Electron 30 or newer on Linux, macOS and Windows. It says future Node.js and Electron releases are covered through Node-API, and names ARM platforms such as Raspberry Pi and Android. For browsers, the listed environments are Chromium, Firefox and Safari.

Those statements apply to the Level package and its selected backends, but they do not mean every application can move unchanged between them. The Node.js constructor uses a directory path for LevelDB files. In a browser, the location is the name of an `IDBDatabase` to open. Calling a Node.js path in browser code does not create a portable file-backed database; browser storage follows the browser-level implementation.

Bundling is another concrete constraint. package.json exposes separate main and browser entries, while the README specifically recommends Browserify, webpack, Rollup or a similar bundler. An application build tool must honor package resolution well enough to select `browser.js` for browser output. A server build can resolve `index.js` and reach classic-level through the normal package entry.

For TypeScript, the README requires generic parameters. This example declares a string-keyed database with `any` values and a sublevel using JSON encoding.

const db = new Level<string, any>('./db', { valueEncoding: 'json' })
const abc = db.sublevel('abc')
const xyz = db.sublevel<string, any>('xyz', { valueEncoding: 'json' })

The type declarations intentionally cover the methods common to both backends. Backend-specific methods must be checked in the classic-level or browser-level documentation instead of inferred from the shared package.

Where the universal package stops

The main limitation is exposed by Level's own documentation boundary. Level follows the `abstract-level` API and delegates additional options and methods to classic-level or browser-level. A developer who needs a capability available only in one implementation cannot assume that code using it will remain portable. The package solves module selection and common operations, not the full differences between native LevelDB access and browser IndexedDB storage.

A second limitation concerns persistence semantics and deployment. In Node.js, the `location` is a filesystem directory containing LevelDB files. In browsers, it is an `IDBDatabase` name. The shared constructor shape does not make those storage environments equivalent. Storage quotas, browser lifecycle behavior, available memory and native filesystem permissions are outside what this README specifies.

The package is also the wrong choice when the application needs a hosted database, multi-process coordination, relational tables or a query planner. No such services are listed among its dependencies or described by its API. A direct backend package can also be clearer when an application targets only one runtime and needs its complete documentation without an abstraction layer.

The documented migration path also deserves attention. The README points existing users to `UPGRADING.md` rather than implying that major-version changes preserve behavior without review. Version 10.0.0 was released on 2025-04-20 after version 9.0.0 on 2024-12-01. Users crossing those major releases should read that file and compare the relevant API and runtime requirements before replacing the installed package.

Choosing Level, classic-level or browser-level

classic-level and browser-level are the relevant alternatives because they are the two backends selected by Level. A Node.js-only project can import classic-level directly and consult its complete README for native-specific options. A browser-only project can do the same with browser-level and its browser support documentation. That removes the portability package, but it also removes the single entry point that maps the same application-facing import across both environments.

Level is the better fit when one codebase must open and use a database through a common API in Node.js and a browser bundle. It is the clearer fit when the team wants TypeScript declarations limited to methods shared by both backends, because it makes the portability boundary visible in the type surface. It also reduces the need for conditional imports at the application layer.

Direct backend selection is more appropriate when the runtime is fixed or a required operation exists only in one backend. It gives the developer immediate access to that package's extra methods and platform details, but it makes cross-runtime code the application's responsibility.

Level is licensed under MIT. The repository includes a LICENSE file, and package.json identifies the same license. That permissive license is relevant when integrating the package into proprietary or other permissively licensed software, subject to the license text's conditions. This repository excerpt does not provide legal interpretation, so the LICENSE file is the controlling source for its obligations.

Release cadence and the cost of staying on Level 10

The repository is not archived. Its last push was on 2026-05-02, and the release list includes v10.0.0 from 2025-04-20, v9.0.0 from 2024-12-01 and v8.0.1 from 2024-01-27. These dates establish recent project activity, but they do not specify a support window or a long-term compatibility guarantee.

The practical upgrade cost depends on the dependency chain. Level 10 depends on `abstract-level` `^3.1.0`, `browser-level` `^3.0.0` and `classic-level` `^3.0.0`. An upgrade can therefore affect not only the convenience package but also the common API declarations and the selected storage implementation. The repository's presence of `CHANGELOG.md` and `UPGRADING.md` gives users specific places to check, while the README does not summarize every breaking change or define a migration policy.

Node.js compatibility is part of this cost. package.json requires Node.js 18 or newer, so applications on older runtimes cannot adopt this release as documented. The README's Node-API statement is relevant to platform compatibility, but teams still need to verify their deployment images, Electron versions and bundler resolution. The package includes `UPGRADING.md` in its published files, so that file is available with the installed package and is the first project-specific document to inspect during an upgrade.

Editorial conclusion

Level 10 fits Node.js and browser applications that need local, lexicographically sorted key-value storage behind the abstract-level API. It is a poor fit for code that requires backend-specific controls, since those remain in classic-level or browser-level, and adopters should first verify their bundler, runtime and dependency compatibility. For this repository, the first concrete check is that the application supports Node.js 18 or newer and accepts the package's native or IndexedDB backend.

Frequently asked questions

Official sources

1. Issues
2. Level/level on GitHub
3. License: MIT
4. README
5. Releases