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+# Changelog
+
+## [1.0.1] - 2022-03-06
+
+### Fixed
+
+- Fix TypeScript type declarations ([`d5db420`](https://github.com/Level/browser-level/commit/d5db420)) (Vincent Weevers)
+
+## [1.0.0] - 2022-03-05
+
+_:seedling: Initial release. If you are upgrading from `level-js`, please see [UPGRADING.md](UPGRADING.md)._
+
+[1.0.1]: https://github.com/Level/browser-level/releases/tag/v1.0.1
+
+[1.0.0]: https://github.com/Level/browser-level/releases/tag/v1.0.0
@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2012 Max Ogden and the contributors to browser-level.
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
@@ -0,0 +1,149 @@
+# browser-level
+
+**An [`abstract-level`][abstract-level] database for browsers, backed by [IndexedDB][indexeddb].** The successor to [`level-js`](https://github.com/Level/level-js). If you are upgrading, please see [UPGRADING.md](UPGRADING.md).
+
+> :pushpin: Which module should I use? What is `abstract-level`? Head over to the [FAQ](https://github.com/Level/community#faq).
+
+[![level badge][level-badge]][awesome]
+[![npm](https://img.shields.io/npm/v/browser-level.svg)](https://www.npmjs.com/package/browser-level)
+[![Test](https://img.shields.io/github/workflow/status/Level/browser-level/Test?label=test)](https://github.com/Level/browser-level/actions/workflows/test.yml)
+[![Coverage](https://img.shields.io/codecov/c/github/Level/browser-level?label=\&logo=codecov\&logoColor=fff)](https://codecov.io/gh/Level/browser-level)
+[![Standard](https://img.shields.io/badge/standard-informational?logo=javascript\&logoColor=fff)](https://standardjs.com)
+[![Common Changelog](https://common-changelog.org/badge.svg)](https://common-changelog.org)
+[![Donate](https://img.shields.io/badge/donate-orange?logo=open-collective\&logoColor=fff)](https://opencollective.com/level)
+
+## Table of Contents
+
+<details><summary>Click to expand</summary>
+
+- [Usage](#usage)
+- [API](#api)
+  - [`db = new BrowserLevel(location[, options])`](#db--new-browserlevellocation-options)
+  - [`BrowserLevel.destroy(location[, prefix][, callback])`](#browserleveldestroylocation-prefix-callback)
+- [Install](#install)
+- [Contributing](#contributing)
+- [Donate](#donate)
+- [License](#license)
+
+</details>
+
+## Usage
+
+```js
+const { BrowserLevel } = require('browser-level')
+
+// Create a database called 'example'
+const db = new BrowserLevel('example', { valueEncoding: 'json' })
+
+// Add an entry with key 'a' and value 1
+await db.put('a', 1)
+
+// Add multiple entries
+await db.batch([{ type: 'put', key: 'b', value: 2 }])
+
+// Get value of key 'a': 1
+const value = await db.get('a')
+
+// Iterate entries with keys that are greater than 'a'
+for await (const [key, value] of db.iterator({ gt: 'a' })) {
+  console.log(value) // 2
+}
+```
+
+<!-- ## Browser Support -->
+
+<!-- [![Sauce Test Status](https://app.saucelabs.com/browser-matrix/level-js.svg)](https://app.saucelabs.com/u/level-js) -->
+
+## API
+
+The API of `browser-level` follows that of [`abstract-level`](https://github.com/Level/abstract-level) with just two additional constructor options (see below) and one additional method (see below). As such, the majority of the API is documented in `abstract-level`. The `createIfMissing` and `errorIfExists` options of `abstract-level` are not supported here.
+
+Like other implementations of `abstract-level`, `browser-level` has first-class support of binary keys and values, using either [Uint8Array](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array) or [Buffer](https://nodejs.org/api/buffer.html). In order to sort string and binary keys the same way as other databases, `browser-level` internally converts data to a Uint8Array before passing them to IndexedDB. If you have no need to work with `Buffer` keys or values, you can choose to omit the [`buffer`](https://github.com/feross/buffer) shim from a JavaScript bundle (through configuration of Webpack, Browserify or other bundlers).
+
+Due to limitations of IndexedDB, `browser-level` does not offer snapshot guarantees. Such a guarantee would mean that an iterator does not see the data of simultaneous writes - it would be reading from a snapshot in time. In contrast, a `browser-level` iterator reads a few entries ahead and then opens a new IndexedDB transaction on the next read. A "few" means all entries for `iterator.all()`, `size` amount of entries for `iterator.nextv(size)` and a hardcoded 100 entries for `iterator.next()`. Individual calls to those methods have snapshot guarantees but repeated calls do not.
+
+The result is that an iterator will include the data of simultaneous writes, if `db.put()`, `db.del()` or `db.batch()` are called in between creating the iterator and consuming the iterator, or in between calls to `iterator.next()` or `iterator.nextv()`. For example:
+
+```js
+const iterator = db.iterator()
+await db.put('abc', '123')
+
+for await (const [key, value] of iterator) {
+  // This might be 'abc'
+  console.log(key)
+}
+```
+
+If snapshot guarantees are a must for your application then use `iterator.all()` and call it immediately after creating the iterator:
+
+```js
+const entries = await db.iterator({ limit: 50 }).all()
+
+// Synchronously iterate the result
+for (const [key, value] of entries) {
+  console.log(key)
+}
+```
+
+### `db = new BrowserLevel(location[, options])`
+
+Create a new database or open an existing one. The required `location` argument is the string name of the [`IDBDatabase`](https://developer.mozilla.org/en-US/docs/Web/API/IDBDatabase) to be opened, as well as the name of the object store within that database. The name of the `IDBDatabase` will be prefixed with `options.prefix`.
+
+Besides `abstract-level` options, the optional `options` argument may contain:
+
+- `prefix` (string, default: `'level-js-'`): Prefix for the `IDBDatabase` name. Can be set to an empty string. The default is compatible with `level-js`.
+- `version` (string or number, default: `1`): The version to open the `IDBDatabase` with.
+
+See [`IDBFactory#open()`](https://developer.mozilla.org/en-US/docs/Web/API/IDBFactory/open) for more details about database name and version.
+
+### `BrowserLevel.destroy(location[, prefix][, callback])`
+
+Delete the IndexedDB database at the given `location`. If `prefix` is not given, it defaults to the same value as the `BrowserLevel` constructor does. The `callback` function will be called when the destroy operation is complete, with a possible error argument. If no callback is provided, a promise is returned. This method is an additional method that is not part of the [`abstract-level`](https://github.com/Level/abstract-level) interface.
+
+Before calling `destroy()`, close a database if it's using the same `location` and `prefix`:
+
+```js
+const db = new BrowserLevel('example')
+await db.close()
+await BrowserLevel.destroy('example')
+```
+
+## Install
+
+With [npm](https://npmjs.org) do:
+
+```bash
+npm install browser-level
+```
+
+This module is best used with [`browserify`](http://browserify.org) or similar bundlers.
+
+<!-- ## Big Thanks
+
+Cross-browser Testing Platform and Open Source ♥ Provided by [Sauce Labs](https://saucelabs.com).
+
+[![Sauce Labs logo](./sauce-labs.svg)](https://saucelabs.com) -->
+
+## Contributing
+
+[`Level/browser-level`](https://github.com/Level/browser-level) is an **OPEN Open Source Project**. This means that:
+
+> Individuals making significant and valuable contributions are given commit-access to the project to contribute as they see fit. This project is more like an open wiki than a standard guarded open source project.
+
+See the [Contribution Guide](https://github.com/Level/community/blob/master/CONTRIBUTING.md) for more details.
+
+## Donate
+
+Support us with a monthly donation on [Open Collective](https://opencollective.com/level) and help us continue our work.
+
+## License
+
+[MIT](LICENSE)
+
+[level-badge]: https://leveljs.org/img/badge.svg
+
+[indexeddb]: https://developer.mozilla.org/en-US/docs/Web/API/IndexedDB_API
+
+[awesome]: https://github.com/Level/awesome
+
+[abstract-level]: https://github.com/Level/abstract-level
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+# Upgrade Guide
+
+This document describes breaking changes and how to upgrade. For a complete list of changes including minor and patch releases, please refer to the [changelog](CHANGELOG.md).
+
+## 1.0.0
+
+**Introducing `browser-level`: a fork of [`level-js`](https://github.com/Level/level-js) that removes the need for [`levelup`](https://github.com/Level/levelup) and more. It implements the [`abstract-level`](https://github.com/Level/abstract-level) interface instead of [`abstract-leveldown`](https://github.com/Level/abstract-leveldown) and thus has the same API as `level` and `levelup` including encodings, promises and events. In addition, you can now choose to use Uint8Array instead of Buffer. Sublevels are builtin.**
+
+We've put together several upgrade guides for different modules. See the [FAQ](https://github.com/Level/community#faq) to find the best upgrade guide for you. This one describes how to replace `level-js` with `browser-level`. There will be a separate guide for `level`.
+
+### What is not covered here
+
+If you are using any of the following, please also read the upgrade guide of [`abstract-level@1`](https://github.com/Level/abstract-level/blob/main/UPGRADING.md#100) which goes into more detail about these:
+
+- Specific error messages (replaced with error codes)
+- The `db.iterator().end()` method (renamed to `close()`, with `end()` as an alias)
+- Zero-length keys and range options (now valid)
+- The `db.supports.bufferKeys` property.
+
+### Changes to initialization
+
+We started using classes, which means using `new` is now required. If you previously did:
+
+```js
+const levelJs = require('level-js')
+const db = levelJs('example')
+```
+
+You must now do:
+
+```js
+const { BrowserLevel } = require('browser-level')
+const db = new BrowserLevel('example')
+```
+
+Arguments and options are the same except that `browser-level` has additional options to control encodings. For backwards compatibility, the `prefix` option has the same default value. Namely `'level-js-'`.
+
+### There is only encodings
+
+The `asBuffer`, `valueAsBuffer` and `keyAsBuffer` options have been replaced with encoding options. The default encoding is `'utf8'` which means operations return strings rather than Buffers by default. If you previously did:
+
+```js
+db.get('example', { asBuffer: false }, callback)
+db.get('example', callback)
+```
+
+You must now do:
+
+```js
+db.get('example', callback)
+db.get('example', { valueEncoding: 'buffer' }, callback)
+```
+
+Or using promises (new):
+
+```js
+const str = await db.get('example')
+const buf = await db.get('example', { valueEncoding: 'buffer' })
+```
+
+Or using Uint8Array (new):
+
+```js
+const arr = await db.get('example', { valueEncoding: 'view' })
+```
+
+### Uint8Array support
+
+A `browser-level` database uses Uint8Array internally, instead of Buffer like `level-js` did. This doesn't change the ability to read existing databases: `browser-level` can read and write databases that were created with `level-js` and vice versa. Externally both Uint8Array and Buffer can be used (see README for details) to maintain backwards- and ecosystem compatibility. You can choose to use Uint8Array exclusively and omit the `buffer` shim from a JavaScript bundle (through configuration of Webpack, Browserify or other bundlers).
+
+### Unwrapping the onion
+
+If you were wrapping `level-js` with `levelup`, `encoding-down` and / or `subleveldown`, remove those modules. If you previously did:
+
+```js
+const levelJs = require('level-js')
+const levelup = require('levelup')
+const enc = require('encoding-down')
+const subleveldown = require('subleveldown')
+
+const db = levelup(enc(levelJs('example')))
+const sublevel = subleveldown(db, 'foo')
+```
+
+You must now do:
+
+```js
+const { BrowserLevel } = require('browser-level')
+const db = new BrowserLevel('example')
+const sublevel = db.sublevel('foo')
+```
+
+### Prefers backpressure over snapshot guarantees
+
+Previously (in `level-js`) an iterator would keep reading in the background, so as to keep the underlying IndexedDB transaction alive and thus not see the data of simultaneous writes. I.e. it was reading from a snapshot in time. This had two major downsides. It was not possible to lazily iterate a large database, as all of the data would be read into memory. Secondly, IndexedDB doesn't actually use a snapshot (the Chrome implementation used to, others never did) but rather a blocking transaction. Meaning you couldn't write to a database while an iterator was active; the write would wait for the iterator to end.
+
+To solve those issues, an iterator now reads a few entries ahead and then opens a new transaction on the next read. A "few" means all entries for `iterator.all()`, `size` amount of entries for `iterator.nextv(size)` and a hardcoded 100 entries for `iterator.next()`. Individual calls to those methods still have snapshot guarantees, but repeated calls do not.
+
+The resulting breaking change is that an iterator will include the data of simultaneous writes, if `db.put()`, `db.del()` or `db.batch()` are called in between creating the iterator and consuming the iterator, or in between calls to `iterator.next()` or `iterator.nextv()`. For example:
+
+```js
+const iterator = db.iterator()
+await db.put('abc', '123')
+
+for await (const [key, value] of iterator) {
+  // This might be 'abc'
+  console.log(key)
+}
+```
+
+To reflect the new behavior, `db.supports.snapshots` is now false. If snapshot guarantees are a must for your application then use `iterator.all()` (which is a new method compared to `level-js`) and call it immediately after creating the iterator:
+
+```js
+const entries = await db.iterator({ limit: 50 }).all()
+
+// Synchronously iterate the result
+for (const [key, value] of entries) {
+  console.log(key)
+}
+```
+
+Unrelated, iterating should now be faster because `browser-level` iterators use the `getAll()` and `getAllKeys()` methods of IndexedDB, instead of a cursor like `level-js` did. This means multiple entries are transferred from IndexedDB to JS in a single turn of the JS event loop, rather than one turn per entry. Reverse iterators do still use a cursor and are therefor slower.
+
+Lastly, the new logic enabled us to implement and fully support `iterator.seek()`.
+
+### Changes to lesser-used properties and methods
+
+- The `db.prefix` property of `level-js`, conflicting with the `db.prefix` property of sublevels, has been renamed to `db.namePrefix`. The relevant constructor option (`prefix`) remains the same.
+- The `db.location`, `db.version` and `db.db` properties are now read-only getters
+- The internal `db.store()` and `db.await()` methods are no longer accessible
+- The `db.upgrade()` utility for upgrading from v4.x to v5.x has been removed.
+
+---
+
+_For earlier releases, before `browser-level` was forked from `level-js` (v6.1.0), please see [the upgrade guide of `level-js`](https://github.com/Level/level-js/blob/HEAD/UPGRADING.md)._
@@ -0,0 +1,111 @@
+import {
+  AbstractLevel,
+  AbstractDatabaseOptions,
+  NodeCallback,
+  AbstractOpenOptions,
+  AbstractGetOptions,
+  AbstractGetManyOptions,
+  AbstractPutOptions,
+  AbstractDelOptions,
+  AbstractBatchOptions,
+  AbstractChainedBatch,
+  AbstractIterator,
+  AbstractKeyIterator,
+  AbstractValueIterator,
+  AbstractIteratorOptions,
+  AbstractKeyIteratorOptions,
+  AbstractValueIteratorOptions,
+  AbstractBatchOperation
+} from 'abstract-level'
+
+/**
+ * An {@link AbstractLevel} database for browsers, backed by [IndexedDB][1].
+ *
+ * @template KDefault The default type of keys if not overridden on operations.
+ * @template VDefault The default type of values if not overridden on operations.
+ *
+ * [1]: https://developer.mozilla.org/en-US/docs/Web/API/IndexedDB_API
+ */
+export class BrowserLevel<KDefault = string, VDefault = string>
+  extends AbstractLevel<Uint8Array, KDefault, VDefault> {
+  /**
+   * Database constructor.
+   *
+   * @param location The name of the [`IDBDatabase`](https://developer.mozilla.org/en-US/docs/Web/API/IDBDatabase)
+   * to be opened, as well as the name of the object store within that database. The name
+   * of the `IDBDatabase` will be prefixed with {@link DatabaseOptions.prefix}.
+   * @param options Options, of which some will be forwarded to {@link open}.
+   */
+  constructor (location: string, options?: DatabaseOptions<KDefault, VDefault> | undefined)
+
+  /**
+   * Location that was passed to the constructor.
+   */
+  get location (): string
+
+  /**
+   * Database name prefix that was passed to the constructor (as `prefix`).
+   */
+  get namePrefix (): string
+
+  /**
+   * Version that was passed to the constructor.
+   */
+  get version (): number
+
+  /**
+   * Delete the IndexedDB database at the given {@link location}.
+   */
+  static destroy (location: string): Promise<void>
+  static destroy (location: string, prefix: string): Promise<void>
+  static destroy (location: string, callback: NodeCallback<void>): void
+  static destroy (location: string, prefix: string, callback: NodeCallback<void>): void
+}
+
+/**
+ * Options for the {@link BrowserLevel} constructor.
+ */
+export interface DatabaseOptions<K, V> extends AbstractDatabaseOptions<K, V> {
+  /**
+   * Prefix for the `IDBDatabase` name. Can be set to an empty string.
+   *
+   * @defaultValue `'level-js-'`
+   */
+  prefix?: string
+
+  /**
+   * The version to open the `IDBDatabase` with.
+   *
+   * @defaultValue `1`
+   */
+  version?: number | string
+
+  /**
+   * An {@link AbstractLevel} option that has no effect on {@link BrowserLevel}.
+   */
+  createIfMissing?: boolean
+
+  /**
+   * An {@link AbstractLevel} option that has no effect on {@link BrowserLevel}.
+   */
+  errorIfExists?: boolean
+}
+
+// Export types so that consumers don't have to guess whether they're extended
+export type OpenOptions = AbstractOpenOptions
+export type GetOptions<K, V> = AbstractGetOptions<K, V>
+export type GetManyOptions<K, V> = AbstractGetManyOptions<K, V>
+export type PutOptions<K, V> = AbstractPutOptions<K, V>
+export type DelOptions<K> = AbstractDelOptions<K>
+
+export type BatchOptions<K, V> = AbstractBatchOptions<K, V>
+export type BatchOperation<TDatabase, K, V> = AbstractBatchOperation<TDatabase, K, V>
+export type ChainedBatch<TDatabase, K, V> = AbstractChainedBatch<TDatabase, K, V>
+
+export type Iterator<TDatabase, K, V> = AbstractIterator<TDatabase, K, V>
+export type KeyIterator<TDatabase, K> = AbstractKeyIterator<TDatabase, K>
+export type ValueIterator<TDatabase, K, V> = AbstractValueIterator<TDatabase, K, V>
+
+export type IteratorOptions<K, V> = AbstractIteratorOptions<K, V>
+export type KeyIteratorOptions<K> = AbstractKeyIteratorOptions<K>
+export type ValueIteratorOptions<K, V> = AbstractValueIteratorOptions<K, V>
@@ -0,0 +1,291 @@
+/* global indexedDB */
+
+'use strict'
+
+const { AbstractLevel } = require('abstract-level')
+const ModuleError = require('module-error')
+const parallel = require('run-parallel-limit')
+const { fromCallback } = require('catering')
+const { Iterator } = require('./iterator')
+const deserialize = require('./util/deserialize')
+const clear = require('./util/clear')
+const createKeyRange = require('./util/key-range')
+
+// Keep as-is for compatibility with existing level-js databases
+const DEFAULT_PREFIX = 'level-js-'
+
+const kIDB = Symbol('idb')
+const kNamePrefix = Symbol('namePrefix')
+const kLocation = Symbol('location')
+const kVersion = Symbol('version')
+const kStore = Symbol('store')
+const kOnComplete = Symbol('onComplete')
+const kPromise = Symbol('promise')
+
+class BrowserLevel extends AbstractLevel {
+  constructor (location, options, _) {
+    // To help migrating to abstract-level
+    if (typeof options === 'function' || typeof _ === 'function') {
+      throw new ModuleError('The levelup-style callback argument has been removed', {
+        code: 'LEVEL_LEGACY'
+      })
+    }
+
+    const { prefix, version, ...forward } = options || {}
+
+    super({
+      encodings: { view: true },
+      snapshots: false,
+      createIfMissing: false,
+      errorIfExists: false,
+      seek: true
+    }, forward)
+
+    if (typeof location !== 'string') {
+      throw new Error('constructor requires a location string argument')
+    }
+
+    // TODO (next major): remove default prefix
+    this[kLocation] = location
+    this[kNamePrefix] = prefix == null ? DEFAULT_PREFIX : prefix
+    this[kVersion] = parseInt(version || 1, 10)
+    this[kIDB] = null
+  }
+
+  get location () {
+    return this[kLocation]
+  }
+
+  get namePrefix () {
+    return this[kNamePrefix]
+  }
+
+  get version () {
+    return this[kVersion]
+  }
+
+  // Exposed for backwards compat and unit tests
+  get db () {
+    return this[kIDB]
+  }
+
+  get type () {
+    return 'browser-level'
+  }
+
+  _open (options, callback) {
+    const req = indexedDB.open(this[kNamePrefix] + this[kLocation], this[kVersion])
+
+    req.onerror = function () {
+      callback(req.error || new Error('unknown error'))
+    }
+
+    req.onsuccess = () => {
+      this[kIDB] = req.result
+      callback()
+    }
+
+    req.onupgradeneeded = (ev) => {
+      const db = ev.target.result
+
+      if (!db.objectStoreNames.contains(this[kLocation])) {
+        db.createObjectStore(this[kLocation])
+      }
+    }
+  }
+
+  [kStore] (mode) {
+    const transaction = this[kIDB].transaction([this[kLocation]], mode)
+    return transaction.objectStore(this[kLocation])
+  }
+
+  [kOnComplete] (request, callback) {
+    const transaction = request.transaction
+
+    // Take advantage of the fact that a non-canceled request error aborts
+    // the transaction. I.e. no need to listen for "request.onerror".
+    transaction.onabort = function () {
+      callback(transaction.error || new Error('aborted by user'))
+    }
+
+    transaction.oncomplete = function () {
+      callback(null, request.result)
+    }
+  }
+
+  _get (key, options, callback) {
+    const store = this[kStore]('readonly')
+    let req
+
+    try {
+      req = store.get(key)
+    } catch (err) {
+      return this.nextTick(callback, err)
+    }
+
+    this[kOnComplete](req, function (err, value) {
+      if (err) return callback(err)
+
+      if (value === undefined) {
+        return callback(new ModuleError('Entry not found', {
+          code: 'LEVEL_NOT_FOUND'
+        }))
+      }
+
+      callback(null, deserialize(value))
+    })
+  }
+
+  _getMany (keys, options, callback) {
+    const store = this[kStore]('readonly')
+    const tasks = keys.map((key) => (next) => {
+      let request
+
+      try {
+        request = store.get(key)
+      } catch (err) {
+        return next(err)
+      }
+
+      request.onsuccess = () => {
+        const value = request.result
+        next(null, value === undefined ? value : deserialize(value))
+      }
+
+      request.onerror = (ev) => {
+        ev.stopPropagation()
+        next(request.error)
+      }
+    })
+
+    parallel(tasks, 16, callback)
+  }
+
+  _del (key, options, callback) {
+    const store = this[kStore]('readwrite')
+    let req
+
+    try {
+      req = store.delete(key)
+    } catch (err) {
+      return this.nextTick(callback, err)
+    }
+
+    this[kOnComplete](req, callback)
+  }
+
+  _put (key, value, options, callback) {
+    const store = this[kStore]('readwrite')
+    let req
+
+    try {
+      // Will throw a DataError or DataCloneError if the environment
+      // does not support serializing the key or value respectively.
+      req = store.put(value, key)
+    } catch (err) {
+      return this.nextTick(callback, err)
+    }
+
+    this[kOnComplete](req, callback)
+  }
+
+  // TODO: implement key and value iterators
+  _iterator (options) {
+    return new Iterator(this, this[kLocation], options)
+  }
+
+  _batch (operations, options, callback) {
+    const store = this[kStore]('readwrite')
+    const transaction = store.transaction
+    let index = 0
+    let error
+
+    transaction.onabort = function () {
+      callback(error || transaction.error || new Error('aborted by user'))
+    }
+
+    transaction.oncomplete = function () {
+      callback()
+    }
+
+    // Wait for a request to complete before making the next, saving CPU.
+    function loop () {
+      const op = operations[index++]
+      const key = op.key
+
+      let req
+
+      try {
+        req = op.type === 'del' ? store.delete(key) : store.put(op.value, key)
+      } catch (err) {
+        error = err
+        transaction.abort()
+        return
+      }
+
+      if (index < operations.length) {
+        req.onsuccess = loop
+      } else if (typeof transaction.commit === 'function') {
+        // Commit now instead of waiting for auto-commit
+        transaction.commit()
+      }
+    }
+
+    loop()
+  }
+
+  _clear (options, callback) {
+    let keyRange
+    let req
+
+    try {
+      keyRange = createKeyRange(options)
+    } catch (e) {
+      // The lower key is greater than the upper key.
+      // IndexedDB throws an error, but we'll just do nothing.
+      return this.nextTick(callback)
+    }
+
+    if (options.limit >= 0) {
+      // IDBObjectStore#delete(range) doesn't have such an option.
+      // Fall back to cursor-based implementation.
+      return clear(this, this[kLocation], keyRange, options, callback)
+    }
+
+    try {
+      const store = this[kStore]('readwrite')
+      req = keyRange ? store.delete(keyRange) : store.clear()
+    } catch (err) {
+      return this.nextTick(callback, err)
+    }
+
+    this[kOnComplete](req, callback)
+  }
+
+  _close (callback) {
+    this[kIDB].close()
+    this.nextTick(callback)
+  }
+}
+
+BrowserLevel.destroy = function (location, prefix, callback) {
+  if (typeof prefix === 'function') {
+    callback = prefix
+    prefix = DEFAULT_PREFIX
+  }
+
+  callback = fromCallback(callback, kPromise)
+  const request = indexedDB.deleteDatabase(prefix + location)
+
+  request.onsuccess = function () {
+    callback()
+  }
+
+  request.onerror = function (err) {
+    callback(err)
+  }
+
+  return callback[kPromise]
+}
+
+exports.BrowserLevel = BrowserLevel
@@ -0,0 +1,238 @@
+'use strict'
+
+const { AbstractIterator } = require('abstract-level')
+const createKeyRange = require('./util/key-range')
+const deserialize = require('./util/deserialize')
+
+const kCache = Symbol('cache')
+const kFinished = Symbol('finished')
+const kOptions = Symbol('options')
+const kCurrentOptions = Symbol('currentOptions')
+const kPosition = Symbol('position')
+const kLocation = Symbol('location')
+const kFirst = Symbol('first')
+const emptyOptions = {}
+
+class Iterator extends AbstractIterator {
+  constructor (db, location, options) {
+    super(db, options)
+
+    this[kCache] = []
+    this[kFinished] = this.limit === 0
+    this[kOptions] = options
+    this[kCurrentOptions] = { ...options }
+    this[kPosition] = undefined
+    this[kLocation] = location
+    this[kFirst] = true
+  }
+
+  // Note: if called by _all() then size can be Infinity. This is an internal
+  // detail; by design AbstractIterator.nextv() does not support Infinity.
+  _nextv (size, options, callback) {
+    this[kFirst] = false
+
+    if (this[kFinished]) {
+      return this.nextTick(callback, null, [])
+    } else if (this[kCache].length > 0) {
+      // TODO: mixing next and nextv is not covered by test suite
+      size = Math.min(size, this[kCache].length)
+      return this.nextTick(callback, null, this[kCache].splice(0, size))
+    }
+
+    // Adjust range by what we already visited
+    if (this[kPosition] !== undefined) {
+      if (this[kOptions].reverse) {
+        this[kCurrentOptions].lt = this[kPosition]
+        this[kCurrentOptions].lte = undefined
+      } else {
+        this[kCurrentOptions].gt = this[kPosition]
+        this[kCurrentOptions].gte = undefined
+      }
+    }
+
+    let keyRange
+
+    try {
+      keyRange = createKeyRange(this[kCurrentOptions])
+    } catch (_) {
+      // The lower key is greater than the upper key.
+      // IndexedDB throws an error, but we'll just return 0 results.
+      this[kFinished] = true
+      return this.nextTick(callback, null, [])
+    }
+
+    const transaction = this.db.db.transaction([this[kLocation]], 'readonly')
+    const store = transaction.objectStore(this[kLocation])
+    const entries = []
+
+    if (!this[kOptions].reverse) {
+      let keys
+      let values
+
+      const complete = () => {
+        // Wait for both requests to complete
+        if (keys === undefined || values === undefined) return
+
+        const length = Math.max(keys.length, values.length)
+
+        if (length === 0 || size === Infinity) {
+          this[kFinished] = true
+        } else {
+          this[kPosition] = keys[length - 1]
+        }
+
+        // Resize
+        entries.length = length
+
+        // Merge keys and values
+        for (let i = 0; i < length; i++) {
+          const key = keys[i]
+          const value = values[i]
+
+          entries[i] = [
+            this[kOptions].keys && key !== undefined ? deserialize(key) : undefined,
+            this[kOptions].values && value !== undefined ? deserialize(value) : undefined
+          ]
+        }
+
+        maybeCommit(transaction)
+      }
+
+      // If keys were not requested and size is Infinity, we don't have to keep
+      // track of position and can thus skip getting keys.
+      if (this[kOptions].keys || size < Infinity) {
+        store.getAllKeys(keyRange, size < Infinity ? size : undefined).onsuccess = (ev) => {
+          keys = ev.target.result
+          complete()
+        }
+      } else {
+        keys = []
+        this.nextTick(complete)
+      }
+
+      if (this[kOptions].values) {
+        store.getAll(keyRange, size < Infinity ? size : undefined).onsuccess = (ev) => {
+          values = ev.target.result
+          complete()
+        }
+      } else {
+        values = []
+        this.nextTick(complete)
+      }
+    } else {
+      // Can't use getAll() in reverse, so use a slower cursor that yields one item at a time
+      // TODO: test if all target browsers support openKeyCursor
+      const method = !this[kOptions].values && store.openKeyCursor ? 'openKeyCursor' : 'openCursor'
+
+      store[method](keyRange, 'prev').onsuccess = (ev) => {
+        const cursor = ev.target.result
+
+        if (cursor) {
+          const { key, value } = cursor
+          this[kPosition] = key
+
+          entries.push([
+            this[kOptions].keys && key !== undefined ? deserialize(key) : undefined,
+            this[kOptions].values && value !== undefined ? deserialize(value) : undefined
+          ])
+
+          if (entries.length < size) {
+            cursor.continue()
+          } else {
+            maybeCommit(transaction)
+          }
+        } else {
+          this[kFinished] = true
+        }
+      }
+    }
+
+    // If an error occurs (on the request), the transaction will abort.
+    transaction.onabort = () => {
+      callback(transaction.error || new Error('aborted by user'))
+      callback = null
+    }
+
+    transaction.oncomplete = () => {
+      callback(null, entries)
+      callback = null
+    }
+  }
+
+  _next (callback) {
+    if (this[kCache].length > 0) {
+      const [key, value] = this[kCache].shift()
+      this.nextTick(callback, null, key, value)
+    } else if (this[kFinished]) {
+      this.nextTick(callback)
+    } else {
+      let size = Math.min(100, this.limit - this.count)
+
+      if (this[kFirst]) {
+        // It's common to only want one entry initially or after a seek()
+        this[kFirst] = false
+        size = 1
+      }
+
+      this._nextv(size, emptyOptions, (err, entries) => {
+        if (err) return callback(err)
+        this[kCache] = entries
+        this._next(callback)
+      })
+    }
+  }
+
+  _all (options, callback) {
+    this[kFirst] = false
+
+    // TODO: mixing next and all is not covered by test suite
+    const cache = this[kCache].splice(0, this[kCache].length)
+    const size = this.limit - this.count - cache.length
+
+    if (size <= 0) {
+      return this.nextTick(callback, null, cache)
+    }
+
+    this._nextv(size, emptyOptions, (err, entries) => {
+      if (err) return callback(err)
+      if (cache.length > 0) entries = cache.concat(entries)
+      callback(null, entries)
+    })
+  }
+
+  _seek (target, options) {
+    this[kFirst] = true
+    this[kCache] = []
+    this[kFinished] = false
+    this[kPosition] = undefined
+
+    // TODO: not covered by test suite
+    this[kCurrentOptions] = { ...this[kOptions] }
+
+    let keyRange
+
+    try {
+      keyRange = createKeyRange(this[kOptions])
+    } catch (_) {
+      this[kFinished] = true
+      return
+    }
+
+    if (keyRange !== null && !keyRange.includes(target)) {
+      this[kFinished] = true
+    } else if (this[kOptions].reverse) {
+      this[kCurrentOptions].lte = target
+    } else {
+      this[kCurrentOptions].gte = target
+    }
+  }
+}
+
+exports.Iterator = Iterator
+
+function maybeCommit (transaction) {
+  // Commit (meaning close) now instead of waiting for auto-commit
+  if (typeof transaction.commit === 'function') {
+    transaction.commit()
+  }
+}
@@ -0,0 +1,56 @@
+{
+  "name": "browser-level",
+  "version": "1.0.1",
+  "description": "An abstract-level database for browsers, backed by IndexedDB",
+  "author": "max ogden",
+  "license": "MIT",
+  "main": "index.js",
+  "types": "./index.d.ts",
+  "scripts": {
+    "test": "standard && ts-standard *.ts && hallmark && airtap -p local --coverage test/index.js && nyc report",
+    "test-browsers": "standard && airtap --coverage test/index.js",
+    "coverage": "nyc report -r lcovonly",
+    "dependency-check": "dependency-check --no-dev .",
+    "prepublishOnly": "npm run dependency-check"
+  },
+  "files": [
+    "index.js",
+    "index.d.ts",
+    "iterator.js",
+    "util",
+    "CHANGELOG.md",
+    "UPGRADING.md",
+    "sauce-labs.svg"
+  ],
+  "dependencies": {
+    "abstract-level": "^1.0.2",
+    "catering": "^2.1.1",
+    "module-error": "^1.0.2",
+    "run-parallel-limit": "^1.1.0"
+  },
+  "devDependencies": {
+    "@voxpelli/tsconfig": "^3.1.0",
+    "airtap": "^4.0.4",
+    "airtap-playwright": "^1.0.1",
+    "airtap-sauce": "^1.1.0",
+    "dependency-check": "^4.1.0",
+    "hallmark": "^4.1.0",
+    "nyc": "^15.0.0",
+    "standard": "^16.0.4",
+    "tape": "^5.5.2",
+    "ts-standard": "^11.0.0",
+    "typescript": "^4.5.5",
+    "uuid": "^3.3.2"
+  },
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/Level/browser-level.git"
+  },
+  "homepage": "https://github.com/Level/browser-level",
+  "keywords": [
+    "level",
+    "leveldb",
+    "indexeddb",
+    "abstract-level"
+  ]
+}
@@ -0,0 +1,81 @@
+<svg
+   xmlns="http://www.w3.org/2000/svg"
+   width="460"
+   height="64"
+   version="1.1"
+   viewBox="0 0 144.37044 20.09272">
+  <defs>
+    <style>
+      .cls-1{isolation:isolate;}
+      .cls-2{opacity:0.15;mix-blend-mode:multiply;}
+      .cls-3{fill:#fff;}
+      .cls-4{fill:#e1251b;}
+      .cls-5{fill:#474c55;}
+    </style>
+  </defs>
+  <title>Sauce Labs</title>
+  <g
+     transform="translate(-0.87516672,-1.0999856)"
+     style="isolation:isolate"
+     id="g3807"
+     class="cls-1">
+    <g
+       id="white">
+      <path
+         style="fill:#e1251b"
+         id="path3774"
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+         class="cls-4" />
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+         class="cls-4" />
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+         class="cls-4" />
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+  </g>
+</svg>
@@ -0,0 +1,35 @@
+'use strict'
+
+module.exports = function clear (db, location, keyRange, options, callback) {
+  if (options.limit === 0) return db.nextTick(callback)
+
+  const transaction = db.db.transaction([location], 'readwrite')
+  const store = transaction.objectStore(location)
+  let count = 0
+
+  transaction.oncomplete = function () {
+    callback()
+  }
+
+  transaction.onabort = function () {
+    callback(transaction.error || new Error('aborted by user'))
+  }
+
+  // A key cursor is faster (skips reading values) but not supported by IE
+  // TODO: we no longer support IE. Test others
+  const method = store.openKeyCursor ? 'openKeyCursor' : 'openCursor'
+  const direction = options.reverse ? 'prev' : 'next'
+
+  store[method](keyRange, direction).onsuccess = function (ev) {
+    const cursor = ev.target.result
+
+    if (cursor) {
+      // Wait for a request to complete before continuing, saving CPU.
+      store.delete(cursor.key).onsuccess = function () {
+        if (options.limit <= 0 || ++count < options.limit) {
+          cursor.continue()
+        }
+      }
+    }
+  }
+}
@@ -0,0 +1,14 @@
+'use strict'
+
+const textEncoder = new TextEncoder()
+
+module.exports = function (data) {
+  if (data instanceof Uint8Array) {
+    return data
+  } else if (data instanceof ArrayBuffer) {
+    return new Uint8Array(data)
+  } else {
+    // Non-binary data stored with an old version (level-js < 5.0.0)
+    return textEncoder.encode(data)
+  }
+}
@@ -0,0 +1,20 @@
+/* global IDBKeyRange */
+
+'use strict'
+
+module.exports = function createKeyRange (options) {
+  const lower = options.gte !== undefined ? options.gte : options.gt !== undefined ? options.gt : undefined
+  const upper = options.lte !== undefined ? options.lte : options.lt !== undefined ? options.lt : undefined
+  const lowerExclusive = options.gte === undefined
+  const upperExclusive = options.lte === undefined
+
+  if (lower !== undefined && upper !== undefined) {
+    return IDBKeyRange.bound(lower, upper, lowerExclusive, upperExclusive)
+  } else if (lower !== undefined) {
+    return IDBKeyRange.lowerBound(lower, lowerExclusive)
+  } else if (upper !== undefined) {
+    return IDBKeyRange.upperBound(upper, upperExclusive)
+  } else {
+    return null
+  }
+}