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https://github.com/Level/memdown

In-memory abstract-leveldown store for Node.js and browsers.
https://github.com/Level/memdown

abstract-leveldown browser javascript level leveldown levelup nodejs

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

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# memdown



**In-memory [`abstract-leveldown`] store for Node.js and browsers.**



> :pushpin: This module will soon be [deprecated](https://github.com/Level/community/issues/113), because it is superseded by [`memory-level`](https://github.com/Level/memory-level).



[![level badge][level-badge]](https://github.com/Level/awesome)

[![npm](https://img.shields.io/npm/v/memdown.svg)](https://www.npmjs.com/package/memdown)

[![Node version](https://img.shields.io/node/v/memdown.svg)](https://www.npmjs.com/package/memdown)

[![Test](https://img.shields.io/github/workflow/status/Level/memdown/Test?label=test)](https://github.com/Level/memdown/actions/workflows/test.yml)

[![Coverage](https://img.shields.io/codecov/c/github/Level/memdown?label=&logo=codecov&logoColor=fff)](https://codecov.io/gh/Level/memdown)

[![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)



## Example



_If you are upgrading: please see [`UPGRADING.md`](./UPGRADING.md)._



```js

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'

  })

})

```



With `async/await`:



```js

await db.put('hey', 'you')

const value = await db.get('hey', { asBuffer: false })

```



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.



## Browser support



[![Sauce Test Status](https://app.saucelabs.com/browser-matrix/level-ci.svg)](https://app.saucelabs.com/u/level-ci)



## Data types



Keys and values can be strings or Buffers. Any other key type will be irreversibly stringified. The only exceptions are `null` and `undefined`. Keys and values of that type are rejected.



```js

const db = levelup(memdown())



db.put('example', 123, (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'

  })

})

```



If you desire non-destructive encoding (e.g. to store and retrieve numbers as-is), 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.



```js

const encode = require('encoding-down')

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



db.put('example', 123, (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) // 'number'

  })

})

```



## Snapshot guarantees



A `memdown` store is backed by [a fully persistent data structure](https://www.npmjs.com/package/functional-red-black-tree) and thus has snapshot guarantees. Meaning that reads operate on a snapshot in time, unaffected by simultaneous writes.



## 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`](https://github.com/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](https://github.com/Level/community/blob/master/CONTRIBUTING.md) for more details.



## 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)



## Donate



Support us with a monthly donation on [Open Collective](https://opencollective.com/level) and help us continue our work.



## License



[MIT](LICENSE)



[`abstract-leveldown`]: https://github.com/Level/abstract-leveldown



[`levelup`]: https://github.com/Level/levelup



[`encoding-down`]: https://github.com/Level/encoding-down



[`leveldown`]: https://github.com/Level/leveldown



[`level-mem`]: https://github.com/Level/mem



[level-badge]: https://leveljs.org/img/badge.svg