memdown

March 29, 2019 · View on GitHub

In-memory abstract-leveldown store for Node.js and browsers.

Example

If you are upgrading: please see the upgrade guide.

const levelup = require('levelup')
const memdown = require('memdown')

const db = levelup(memdown())

db.put('hey', 'you', (err) => {
  if (err) throw err

  db.get('hey', { asBuffer: false }, (err, value) => {
    if (err) throw err
    console.log(value) // 'you'
  })
})

Your data is discarded when the process ends or you release a reference to the store. Note as well, though the internals of memdown operate synchronously - levelup does not.

Unlike leveldown, memdown does not stringify keys or values. This means that in addition to Buffers, you can store any JS type without the need for encoding-down. For keys for example, you could use Buffers or strings, which sort lexicographically, or numbers, even Dates, which sort naturally. The only exceptions are null and undefined. Keys and values of that type are rejected.

const db = levelup(memdown())

db.put(12, true, (err) => {
  if (err) throw err

  db.createReadStream({
    keyAsBuffer: false,
    valueAsBuffer: false
  }).on('data', (entry) => {
    console.log(typeof entry.key) // 'number'
    console.log(typeof entry.value) // 'boolean'
  })
})

If you desire normalization for keys and values (e.g. to stringify numbers), wrap memdown with encoding-down. Alternatively install level-mem which conveniently bundles levelup, memdown and encoding-down. Such an approach is also recommended if you want to achieve universal (isomorphic) behavior. For example, you could have leveldown in a backend and memdown in the frontend.

const encode = require('encoding-down')
const db = levelup(encode(memdown()))

db.put(12, true, (err) => {
  if (err) throw err

  db.createReadStream({
    keyAsBuffer: false,
    valueAsBuffer: false
  }).on('data', (entry) => {
    console.log(typeof entry.key) // 'string'
    console.log(typeof entry.value) // 'string'
  })
})

Snapshot guarantees

A memdown store is backed by a fully persistent data structure and thus has snapshot guarantees. Meaning that reads operate on a snapshot in time, unaffected by simultaneous writes. Do note memdown cannot uphold this guarantee for (copies of) object references. If you store object values, be mindful of mutating referenced objects:

const db = levelup(memdown())
const obj = { thing: 'original' }

db.put('key', obj, (err) => {
  obj.thing = 'modified'

  db.get('key', { asBuffer: false }, (err, value) => {
    console.log(value === obj) // true
    console.log(value.thing) // 'modified'
  })
})

Conversely, when memdown is wrapped with encoding-down it stores representations rather than references.

const encode = require('encoding-down')

const db = levelup(encode(memdown(), { valueEncoding: 'json' }))
const obj = { thing: 'original' }

db.put('key', obj, (err) => {
  obj.thing = 'modified'

  db.get('key', { asBuffer: false }, (err, value) => {
    console.log(value === obj) // false
    console.log(value.thing) // 'original'
  })
})

Test

In addition to the regular npm test, you can test memdown in a browser of choice with:

npm run test-browser-local

To check code coverage:

npm run coverage

Contributing

Level/memdown 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 for more details.

memdown

Example

Browser support

Data types

Snapshot guarantees

Test

Contributing

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