js-hashbelt

According to NIST:

> hashbelt (data structure) :: Use a short list or array of hash tables to implement a hash table with aging to expire items. To expire items, add a new table at the head of the list and drop the oldest table, along with its contents. To find an item, search all the tables.

Install

``sh
npm install hashbelt
`

Use

`javascript
import hashbelt from 'hashbelt'

let belt = hashbelt({
max: 4, // keep 4 belt entries (default)
interval: 60000, // rotate every minute (default)
step: Object, // create a new belt entry (default is {})
})


// or pass a step() function
let belt_map = hashbelt( () => new Map() )

// or perhaps you'd like a WeakMap?
let belt_weak = hashbelt( () => new WeakMap() )
`

API of Hashbelt Result

Expired entries will be pop()'d from the end of the belt.
The first index is the most recent "tip" of the hashbelt.

`javascript
belt.rotate() // force a belt rotation
belt.step() // create a belt entry (does not insert it)
clearInterval(belt.tid) // belt.tid is the interval handle; unref'd by default

Array.isArray(belt) // belt is just an array with extra attributes

// use index 0 to access the tip
belt[0]['my_key'] = 1942
belt_map[0].set('my_key', 2042)

// use array methods or iterate the belt to consult all entries
belt.find(each => each['my_key'])
belt_map.find(map => map.has('my_key'))
``

$3

To make this module more generally useful, I've changed to a minimal hashbelt
implementation ported from [msg-fabric-core/code/timeouts.jsy][msgfab]. This
change drops rarely used features such as copy forward caching and JS Map
compatibility. In exchange, the library weighs in at ~300 bytes minified, and
~200 bytes with brotli.

[msgfab]: https://github.com/msg-fabric/msg-fabric-core/blob/master/code/timeouts.jsy