Weaker.js

WeakerMaps are enumerable Maps with with weak values rather than keys.

WeakerSet are like WeakSets, but enumerable, and clearable.

Install

Both

npm install weaker

const WeakerMap = require('weaker/WeakerMap');
const WeakerSet = require('weaker/WeakerSet');

One or the other

npm install weakermap
npm install weakerset

const WeakerMap = require('weakermap');
const WeakerSet = require('weakerset');

About

Docs

WeakerMap

WeakerSet

WeakerMap

This class implements a pattern similar to the 'WeakMap', however its values are weakly referenced, rather than the keys. This allows for enumeration, clearing and arbitrarily valued keys, with the limitation that the values must be objects. Note that elements may not be garbage collected immediately upon leaving a given scope, however this should not have an impact on memory, since the memory will not be freed until the garbage collector runs, with or without the WeakerMap. See MDN's notes on WeakRefs for more info.

WeakerSet

This class implements a pattern similar to the WeakSet, but allows for enumeration and clearing. Ironically, the implementation depends on a WeakerMap and a WeakMap in tandem, managing a group of WeakRefs. Note that elements may not be garbage collected immediately upon leaving a given scope, however this should not have an impact on memory, since the memory will not be freed until the garbage collector runs, with or without the WeakerSet. See MDN's notes on WeakRefs for more info.

Examples

WeakerMap

A WeakerMap will only hold onto its values as long as they aren't garbage collected. Once that happens they will be removed without any furter intervention from the programmer.

NOTE: The following example makes use of global.gc() to force garbage collection to run regardless of existing heuristics. This requires node to be run with the --expose-gc flag. This is not necessary except to demonstrate the behavior in a short script, where the garbage collector would not normally run until the program exits.

const WeakerMap = require('weaker/WeakerMap');

const wm = new WeakerMap;
const retain  = [];

{
	let a = {a:1}, b = {b:2}, c = {c:3};

	[ ['a', a], ['b', b], ['c', c] ].forEach(e => wm.set(...e));

	retain.push(b,c);
};

const printRemaining = () => {
	retain;       // keep refs in-scope
	global.gc();  // force the garbage collector
	console.log(wm.values());
};

printRemaining();
// The garbage collector hasn't run yet,
// So we still have all three refs
// [ { a: 1 }, { b: 2 }, { c: 3 } ]

setTimeout(printRemaining, 500);
// Once we swap to a new 'job', it can run
// and we only have two objects now:
// [ { b: 2 }, { c: 3 } ]

WeakerSet

A WeakerSet will only hold onto its values as long as they aren't garbage collected. Once that happens they will be removed without any furter intervention from the programmer.

NOTE: The following example makes use of global.gc() to force garbage collection to run regardless of existing heuristics. This requires node to be run with the --expose-gc flag. This is not necessary except to demonstrate the behavior in a short script, where the garbage collector would not normally run until the program exits.

const WeakerSet = require('weaker/WeakerSet');

const ws = new WeakerSet;
const retain  = [];

{
	let a = {a:1}, b = {b:2}, c = {c:3};

	[ a, b, c ].forEach(e => ws.add(e));

	retain.push(b,c);
};

const printRemaining = () => {
	retain;       // keep refs in-scope
	global.gc();  // force the garbage collector
	console.log(ws.values());
};

printRemaining();
// The garbage collector hasn't run yet,
// So we still have all three refs
// [ { a: 1 }, { b: 2 }, { c: 3 } ]

setTimeout(printRemaining, 500);
// Once we swap to a new 'job', it can run
// and we only have two objects now:
// [ { b: 2 }, { c: 3 } ]

Testing

npm test