async-level

Create an async friendly interface around leveldown.

Lightweight, zero dependency, single file alternative to levelup.

Example (put, get)

const LevelDown = require('leveldown')
const AsyncLevel = require('async-level')

const leveldown = LevelDown('/db/path')
const db = new AsyncLevel(leveldown, {
  encode: JSON.stringify,
  decode: JSON.parse
})

const { err: openErr } = await levelDB.open()
if (openErr) throw

const { err } = await levelDB.put('foo#three', {
  id: 'user id',
  email: '[email protected]'
})

const { err, data: value } = await levelDB.get('foo#one')
// value is decoded, with JSON.parse.

Example (async iterator)

const LevelDown = require('leveldown')
const AsyncLevel = require('async-level')

const leveldown = LevelDown('/db/path')
const db = new AsyncLevel(leveldown, {
  encode: JSON.stringify,
  decode: JSON.parse
})

const { err: openErr } = await levelDB.open()
if (openErr) throw

// This returns an AsyncIterator instead of returning a leveldown
// iterator object.
// You can use for await (const pair of itr) loops over it.
const itr1 = levelDB.iterator({
  gte: 'foo' + '\x00',
  lte: 'foo' + '\xFF',
  keyAsBuffer: false
})

const result = await itr.next()
// result.done
// result.value.err
// The data here is decoded with JSON.parse
// result.value.data

Example (batch)

const LevelDown = require('leveldown')
const AsyncLevel = require('async-level')

const leveldown = LevelDown('/db/path')
const db = new AsyncLevel(leveldown, {
  encode: JSON.stringify,
  decode: JSON.parse
})

const { err: openErr } = await levelDB.open()
if (openErr) throw

const { err } = await levelDB.batch([
  {
    type: 'put',
    key: 'foo#one',
    value: { any: 'json object' }
  },
  {
    type: 'put',
    key: 'foo#two',
    value: { your: 'encode func called' }
  }
])

Example (key encoding)

const LevelDown = require('leveldown')
const AsyncLevel = require('async-level')
const charwise = require('charwise-compact')

const leveldown = LevelDown('/db/path')
const db = new AsyncLevel(leveldown, {
  encode: JSON.stringify,
  keyEncode: charwise.encode,
  decode: JSON.parse
})

await levelDB.open()

const { err } = await levelDB.put(['foo', 'three'], {
  id: 'use id',
  email: '[email protected]'
})

const { err, data: value } = await levelDB.get(['foo', 'one'])
// value is decoded, with JSON.parse.

const itr1 = levelDB.iterator({
  gte: ['foo', charwise.LO],
  lte: ['foo', charwise.HI],
  keyAsBuffer: false
})

Motivation

A simpler API around leveldown with basic features like

• async/await support, including { err, data } = await
• encode, decode & keyEncode
• iterator() method that returns AsyncIterator

This library returns { err, data } from all it's promises like documented in resultify

The alternative library level has quite a bit of code and weight in it, including features we do not need like streams and normal promises that reject/throw.

This alterive library async-level is single file, zero dependencies and clocks in at <500 lines of code.

Documentation

AsyncLevel provides a class to wrap leveldown and adds some quality of life API improvements including promises, encode, decode & keyEncode as well as iterator returning an AsyncIterator.

Currently the AsyncIterator does not support concurrent calls to next()

CAVEAT

Also note that this is a wrapped around leveldown; so it has all the same caveats as leveldown, for example if you call get() before open() finishes your node program just segfaults

const db = new AsyncLevel(leveldown, options)

Calling AsyncLevel with leveldown and options creates a db object.

• leveldown must be an instance of leveldown
• options.encode is an optional encoding function like JSON.stringify
• options.decode is an optional decoding function like JSON.parse
• options.keyEncode is an optional key encoding function like require('charwise').encode
• options.valueEncoding ; for backwards compatibility with level you can set options.valueEncoding: 'json' to enable JSON.parse & JSON.stringify for decode & encode.

await db.ensure()

You cannot interact with leveldown until the database is open.

Calling await db.ensure() will wait until the database is open.

levelup had a feature where it would enqueue all your reads and writes until the database is open.

Instead, with async-level you can add await db.ensure() to the top of any method that wants to do any reads or writes on a potentially un-open database. This will ensure the database is open.

const { err } = await db.open()

Open the database and get an err back if it failed.

const { err } = await db.close()

Close the database and get an err back if it failed.

const { err } = await db.put(key, value)

Write a key/value to the database. Get an err back if it failed.

If you specified encode, decode or keyEncode in the constructor then those will be respected for encoding of key and value.

const { err, data } = await db.get(key)

Retrives a key from the database. Get an err or a data back.

If you specified encode, decode or keyEncode in the constructor then those will be respected for encoding of key and data.

If the key is not found then it will return an err which has a err.notFound === true property on it.

const { err } = await db.del(key)

Deletes a key from the database. Get an err back if it failed.

If you specified keyEncode in the constructor then it will be respected for encoding of key

const { err } = await db.batch(operations)

Writes a batch to the database. Get an err back if it failed.

The operations parameter must be an Array of objects with three properties, type, key and value.

The type field can be 'put' or 'del'

If you specified encode, decode or keyEncode in the constructor then those will be respected for encoding of key and value.

const { err } = await db.clear(options)

Clear a range of key/value pairs in the levelDB database. Options are passed to leveldown.clear() and include: gt, gte, lt, lte, reverse, limit.

const itr = db.iterator(options)

Creates an AsyncIterator for the database. Note that this method does not return a promise and does not need await.

The AsyncIterator returned is compatible with for await loops.

If you specified encode, decode or keyEncode in the constructor then those will be respected for encoding of key and value.

See leveldown.iterator() docs

The options object is passed to leveldown.iterator()

const r = await itr.next()

Gets the next key/value pair from the iterator. This returns an IteratorResult with r.done and r.value.

If r.done is true then the iterator is finished. The r.value contains r.value.err and r.value.data.

If there was an err reading from the iterator then you get r.value.err otherwise r.value.data contains a key and a value.

Aka r.value.data.key and r.value.data.value are returned from the iterator for the key and value.

• r.done; boolean, if true the iterator is finished
• r.value.err; optional Error; if it exists then there was an error
• r.value.data.key; the key for this iterator value
• r.value.data.value; the value for this iterator value.

const { err } = await itr.close()

This closes the iterator. Must be closed if you do not read the iterator to completion.

const r = await itr.batchNext()

Like next() but returns keys and values aka

• r.value.data.keys; an array of keys
• r.value.data.values; an array of values.

If you use batchNext() we recommend using a decent highWaterMark

const itr = db.iterator({
  gt: '...',
  lte: '...',
  highWaterMark: 1024 * 1024
})

batchNext() optimization.

For some applications it's really useful to read a batch of key value pairs out of the Iterator in one go.

The AsyncIterator supports an await batchNext() method that returns an array of keys & an array of values.

The maximum length is 1000 and the maximum size is based on the highWaterMark that you pass to leveldown (default 16kb).

install

% npm install async-level

MIT License.