fastify-riotjs-and-lowdb/node_modules/levelup/UPGRADING.md

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.

v4

There have been two major updates to dependencies. First, level-iterator-stream is now based on readable-stream@3. Second, deferred-leveldown is now based on abstract-leveldown@6. Please follow these links for more information; both contain significant enough changes to warrant this levelup major. In addition, all aforementioned dependencies and by extension levelup have dropped support of IE10.

To get a consistent behavior between opening and opened levelup instances (in the former case, your store will be wrapped with deferred-leveldown), we recommend to pair levelup@4 only with a store based on abstract-leveldown >= 6. For example, deferred-leveldown now rejects null and undefined values. If you pair levelup@4 with an older store, db.put('key', null) would only throw an error if db is still opening itself.

v3

1. Dropped support for node 4.
2. Batch operations no longer default to 'put'. If type isn't specified, an error will be thrown, courtesy of abstract-leveldown.

v2

Summary

There has been quite some work done for this new major version:

1. Make levelup more generic by reducing focus on leveldown and LevelDB.
2. Make levelup more generic by removing code related to encodings, which would allow *down implementations to manage encodings themselves.
3. Use standard as linter to avoid bikeshedding.
4. Add a native Promise API for promise using geeks. Many have been asking for this. Also async/await is awesome. Breaking change: previously, if you did not pass a callback to an async function and there was an error, levelup would emit an error event instead. This is no longer true.

Point 1 and 2 also helps out with reducing complexity.

Upgrade Guide

Since levelup no longer tries to load leveldown as a default backend you have to provide a backend instance yourself.

So if you previously did:

$ npm i levelup leveldown --save

And in your code you did something like:

const levelup = require('levelup')
const db = levelup('/path/to/db')

You should now do (for identical functionality):

const levelup = require('levelup')
const encode = require('encoding-down')
const leveldown = require('leveldown')
const db = levelup(encode(leveldown('/path/to/db')))

Note that we have moved out encodings into encoding-down, which in itself is a *down that wraps a *down (meta ftw). It basically just sits in between levelup and the actual backend to operate on encodings for keys and values. Default encoding is 'utf8' like before.

This obviously means everyone has to do a lot of code rewrite which is bad. So we aim to fix this by putting that code into level@2.0.0, which already is used as a convenience package.

Switching from levelup and leveldown combo to only using level you would do:

const level = require('level')
const db = level('/path/to/db')

Also, we aim to simplify using memdown in the same way by updating level-mem.

For more advanced usage with custom versions of abstract-leveldown, the first parameter to levelup() should be an abstract-leveldown instead of passing a factory function via options.db.

So if you previously did:

const db = levelup('/path/to/db', {
  db: function (location) {
    return new CustomLevelDOWN(location)
  }
})

You should now do (for identical functionality):

const encode = require('encoding-down')
const db = levelup(encode(new CustomLevelDOWN('/path/to/db')))