weak-merge

A module for merging WeakSets and WeakMaps.

Install

$ npm i weak-merge

Usage

import { mergeWeakMaps, mergeWeakSets } from 'weak-merge'

const [a, b, c, d] = [{}, {}, {}, {}]

const weakSet1 = new WeakSet([a, b])
const weakSet2 = new WeakSet([c])

const mergedWeakSet = mergeWeakSets(weakSet1, weakSet2)

console.log([a, b, c].map(key => mergedWeakSet.has(key)))
//=> [ true, true, true ]

mergedWeakSet.delete(a)
console.log(mergedWeakSet.has(a))
//=> false

console.log(weakSet1.has(a))
//=> true

mergedWeakSet.add(d)
console.log(mergedWeakSet.has(d))
//=> true

console.log(weakSet1.has(d))
//=> false

const weakMap1 = new WeakMap([
  [a, 1],
  [b, 2],
])
const weakMap2 = new WeakMap([[c, 3]])

const mergedWeakMap = mergeWeakMaps(weakMap1, weakMap2)

console.log([a, b, c].map(key => mergedWeakMap.get(key)))
//=> [ 1, 2, 3 ]

mergedWeakMap.delete(a)
console.log(mergedWeakMap.has(a))
//=> false

console.log(weakMap1.has(a))
//=> true

mergedWeakMap.set(a, 5)
console.log(mergedWeakMap.get(a))
//=> 5

console.log(weakMap1.get(a))
//=> 1

See the TypeScript types for more documentation.

Why?

Merging WeakSet or WeakMap instances is not trivial because they are not enumerable.

Performance

WeakSet instances returned from mergeWeakSets and WeakMap instances returned from mergeWeakMaps are not as performant as native WeakSet and WeakMap instances (due to the lack of a native way to merge or copy WeakSet and WeakMap instances):

WeakSet Time Complexity

Operation	Native WeakSet	Merge of n native WeakSet instances
add	O(1)	O(1)
delete	O(1)	O(1)
has	O(1)	O(n)

WeakMap Time Complexity

Operation	Native WeakMap	Merge of n native WeakMap instances
delete	O(1)	O(1)
get	O(1)	O(n)
has	O(1)	O(n)
set	O(1)	O(1)

Contributing

Stars are always welcome!

For bugs and feature requests, please create an issue.

For pull requests, please read the contributing guidelines.

License

Apache License 2.0

This is not an official Google product.