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

npm install hashbelt

Use

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.

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'))

2022 update (breaking changes)

To make this module more generally useful, I've changed to a minimal hashbelt implementation ported from msg-fabric-core/code/timeouts.jsy. 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.