lfu-cache for Node.js

This module implements an O(1) Least Frequently Used cache, as described in the paper "An O(1) algorithm for implementing the LFU cache eviction scheme" by K. Shah, A. Mitra and D. Matani.

It also features a "decay" parameter (default null, no decay) that penalizes objects that have not been accessed after Date.now() - decay, by halving their frequency every 'decay' milliseconds.

Important: decay happens at most every decay milliseconds, and it's a costly operation, so this parameter should not be too small (a minute is good).

The cache emits an "eviction" event with parameters (key, value), when a least frequently used element has been evicted to make room for the cache.

Usage

var lfu = require('lfu-cache')(
	2,   // max size of the cache
	60000    // decay of the entries in milliseconds
);

lfu.on('eviction', function(key, obj) {
	console.log("test was evicted", key, obj);
});
lfu.set('test', {my: "val"});
lfu.set('test2', {my: "val2"});
lfu.get('test2');
lfu.set('test3', {my: "val2"});