WeakerSet

Like WeakSets, but enumerable, and clearable.

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.

Install

npm install weakerset

import { WeakerSet } from 'weakerset';

Methods

WeakerSet.construct(entries)

Create a new WeakerSet object, optionally prepopulated by entries.

Parameters

• entries - An iterable list of objects to add to the set.

Returns

A newly constructed WeakerSet object.

const ws = new WeakerSet([ {a:1}, {b:2}, {c:3} ]);

[Symbol.iterator]()

Traverse the entries.

Parameters

none

Returns

A new Iterator that traverses the WeakerSet.

const ws = new WeakerSet([ {a:1}, {b:2}, {c:3} ]);

for(const entry of ws)
{
    console.log(entry);
}
// { a: 1 }
// { b: 2 }
// { c: 3 }

const ws = new WeakerSet([ {a:1}, {b:2}, {c:3} ]);
const ar = [...ws];

console.log(ar);
// [
//     { a: 1 },
//     { b: 2 },
//     { c: 3 }
// ]

const ws = new WeakerSet([ {a:1}, {b:2}, {c:3} ]);

[...ws].map( entry => console.log( entry ));
// { a: 1 }
// { b: 2 }
// { c: 3 }

WeakerSet.add(obj)

Add an object.

Parameters

• obj - The object to add to the set.

Returns

none

const ws = new WeakerSet;

ws.add({a:1});

WeakerSet.clear()

Clear the WeakerSet.

const ws = new WeakerSet([ {a:1}, {b:2}, {c:3} ]);

ws.clear();

console.log( ws.size ); // 0

WeakerSet.delete(obj)

Delete an object from the set.

Parameters

• obj - The object to delete from the set.

Returns

none

const a = {a:1};
const b = {b:2};
const c = {c:3};

const ws = new WeakerSet([ a, b, c ]);

ws.delete(b);

WeakerSet.entries()

Traverse all entries.

Parameters

none

Returns

A new Iterator that traverses the WeakerSet. Each entry is a pair [key, value] where both key and value are the same object.

const ws = new WeakerSet([ {a:1}, {b:2}, {c:3} ]);

for(const [key, value] of ws.entries())
{
    console.log({key, value});
}
// {key: {a: 1}, value: {a: 1}}
// {key: {b: 1}, value: {b: 1}}
// {key: {c: 1}, value: {c: 1}}

WeakerSet.forEach()

Traverse all entries with a callback.

Parameters

• callback - a function to run on each entry.

Returns

none

const ws = new WeakerSet([ {a:1}, {b:2}, {c:3} ]);

ws.forEach((value, key, set) => {
    console.log({value, key});
});

WeakerSet.has(obj)

Check for the presence of a key.

Parameters

• obj - The object to look up in the set.

Returns

true if the object obj is present, or false if not found.

const a = {a:1};
const b = {b:2};
const c = {c:3};

const ws = new WeakerSet([ a, b, c ]);

console.log( ws.has(b) ); // true
console.log( ws.has(g) ); // false

WeakerSet.keys()

Traverse all values (keys are not explicitly stored, so keys() returns the same thing as values()).

Parameters

none

Returns

A new Iterator that traverses the WeakerSet.

const ws = new WeakerSet([ {a:1}, {b:2}, {c:3} ]);

for(const key of ws.keys())
{
    console.log(key);
}
// {a:1}
// {b:2}
// {c:3}

WeakerSet.values()

Traverse all values.

Parameters

none

Returns

A new Iterator that traverses the WeakerSet.

const ws = new WeakerSet([ {a:1}, {b:2}, {c:3} ]);

for(const value of ws.values())
{
    console.log(value);
}
// {a:1}
// {b:2}
// {c:3}

Example

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 further 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.

import { WeakerSet } from '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 } ]

🍻 Licensed under the Apache License, Version 2.0

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

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