A safe cache for mutable objects


Do you want to cache an object and then mutate it without affecting the cached representation? Yes? Then this is the cache for you.

Should this happen?

NODE> cache.put('x', {a: 'a', b: 'b', c: 'c'})
{ a: 'a', b: 'b', c: 'c' }
NODE> cache.get('x')
{ a: 'a', b: 'b', c: 'c' }
NODE> var theValueNow = cache.get('x')
NODE> delete theValueNow.a
NODE> delete theValueNow.b
NODE> delete theValueNow.c
NODE> = true
NODE> cache.get('x')
{ lol: true }

I don't think so. This cache won't do that.

npm install mutacache --save

The simplest case, storing a primitive:

var cache = require('mutacache')();
cache.put('key', 'value');
if (cache.has('key')) {
  cache.get('key'); // returns 'value' 

Storing an object:

var cache = require('mutacache')();
cache.put('key', {a:'a', b:'b', c:'c'});
if (cache.has('key')) {
  var x = cache.get('key');  //returns {a:'a', b:'b', c:'c'} 
  x.= 'lol';
  cache.get('key');  // still returns {a:'a', b:'b', c:'c'} 

The mutacache function takes an object of options,

  • cacheFunctions A boolean, defines whether functions should be cached. Default false.

Caching functions is useful, but it's use invokes an alternate copying mechanism that has performance penalties.

This is probably applicable for more than Function types.

var nonFnCacher = require('mutacache')();
var fnCacher = require('mutacache')({cacheFunctions:true});
function abc() {
  // something important here 
nonFnCacher.put('key', {a:'a', fn:abc});
if (nonFnCacher.has('key')) {
  var x = nonFnCacher.get('key');  //returns {a:'a'} 
fnCacher.put('key', {a:'a', fn:abc});
if (fnCacher.has('key')) {
  var x = fnCacher.get('key');  //returns {a:'a', fn:abc} 

This cache copies values on insertion and retrieval, and Javascript data structures aren't really built for that. Don't use this if you're looking for raw speed.

And, some TODOs:

  • Add cache busting
  • TTLs

Copyright © 2014 Dan Midwood

Distributed under the Apache License, Version 2.0