weakness

Provides an iterable weak sequence.

When adding elements to the weakness, you must specify a "keeper" object. The keeper will maintain a strong reference to the element. When the keeper is garbage collected, and there are no other strong references to the element, the element will be automatically removed from the weakness.

A contrived example:

interface O {
  x:number
}

let keeper = {}
const w = new Weakness<O>()
w.add(keeper, {x:0})
w.add(keeper, {x:1})
w.add(keeper, {x:2})
console.log([...w]) // [{x:0}, {x:1}, {x:2}]
keeper = undefined
// wait for garbage collection
console.log([...w]) // []

The add method returns a number that you can subsequently use to remove the item from the weakness, via its delete method:

const w = new Weakness<O>()
const keeper = {}
const n = w.add(keeper, {x:0})
console.log([...w]) // [{x:0}]
w.delete(n)
console.log([...w]) // []

That's it. This is useful for signalling libraries, to prevent consumers from having to track and clean up their signal usage.