Koop Memory Cache

[![npm version][npm-img]][npm-url]
!coverage

This is a LRU cache with ttl (time to live) expiry. It expects cache items to be GeoJSON feature collections. It is based on quick-lru.

Cache eviction occurs in two ways:
1. if the cache grows to a number of items greater than the cache's defined size, the least recently inserted or accessed item is evicted
2. if a item is accessed and it has gone past its ttl period, it is evicted

Usage

$3

``js
const Cache = require('@koopjs/cache-memory');
const cache = new Cache({ size: 1000 });
`

$3

This is the default cache for Koop so you won't need to instantiate it yourself. If you really wanted to, it would look like this:

`js
const Koop = require('koop')
const koop = new Koop()
const cache = require('@koopjs/cache-memory')
koop.register(cache, { size: 1000 })
`
#### Options
size: the maximum number of items to store in the queue before evicting the least recently used item.

Cache API

The cache is a JavaScript object that lives in-memory. It is used to store geojson features.

$3

Insert geojson into the cache.


`js
const geojson = {
type: 'FeatureCollection',
features: [],
metadata: {
name: 'Example GeoJSON',
description: 'This is geojson that will be stored in the cache'
}
}

const options = {
ttl: 1000 // The TTL option is measured in seconds, it will be used to set the maxAge property in the LRU cache
}

cache.insert('key', geojson, options, err => {
// This function will call back with an error if one occurs
})
`

$3

Retrieve a cached feature collection.

`js
const options = {
pick: [] // an array of keys used to return a subset of the feature collections root level properties
omit
}

cache.retrieve('key', options, (err, geojson) => {
/* This function will callback with an error or the data cached with the passed key. It will return undefined if not found or expired.
{
type: 'FeatureCollection',
features: [],
metadata: {}
}
*/
})
`

$3

Remove a feature collection from the cache

`js
cache.delete('key', err => {
// This function will call back with an error if one occurs
})
``

[npm-img]: https://img.shields.io/npm/v/@koopjs/cache-memory.svg?style=flat-square
[npm-url]: https://www.npmjs.com/package/@koopjs/cache-memory