The idea is that TwoWayWeakMap would work like WeakMap, except that you would be able to get key objects by their value. For example, here is how the usage would look like: class TwoWayWeakMap { // What goes here? } class SomeClass {} const map = new TwoWayWeakMap<SomeClass, number>() function…

console.log keeps the object alive. Strangely enough, even if you only print it once, then clear the console. Adjust these two lines so that console.log doesn't get hold of the object: console.log(`o still exists? (${tick++})`, !!obj); ... console.log(!!map.keyFrom(42));

I think there's also a bug/typo in this part: for (const ref of this.#refs) { const o = ref.deref(); if (!o) { this.#refs.delete(ref); return undefined; // <<< I don't think returning here is correct, the ref could have been for a different key/value pair } if (this.…

[image] aclaymore: return undefined Hey, thanks! I had since then already changed that return undefined to continue. That's what I meant. The example in the original post works now. I wonder if it would be a bad practice to use this though. Like, for example, if some piece of code keeps acc…

You probably just want to combine a WeakMap for object key to value and a WeakValueMap for value to object key which needs a finalization registry to clear things. You should never need to iterate over a set, or defer unless you actually mean to access that value. I'll try to write your TwoWayWeakMa…

Alright it ended up being a little trickier than I thought, but here is a TwoWayWeakMap that should be rock solid: TwoWayWeakMap for https://es.discourse.group/t/how-to-implement-twowayweakmap-using-weakref/890 · GitHub I switched your keyFrom to a keysFor since there can be multiple values with th…

BTW, your gist will still leak because you still keep a strong reference from the key to the value, just indirectly . Here's a corrected (and cleaner) version, with a bunch of comments explaining why each bit is the way it is. (Note: I've omitted the extras suggested here for better algorithmic clari…

I believe we're solving 2 different problems. I understood the request as being able to find all the keys of a WeakMap that have a given value, but besides that for the map to still be a regular WeakMap where keys are held weakly, but the value strongly associated to the key. You are implementing a…

[image] claudiameadows: Given how tricky this is to write correctly Agreed it's extremely tricky to write those right, and I'm surprised no-one has published various weak collections on npm yet.

I'm used to the following taxonomy: Strong key, strong value = Map Strong key, weak value = what I normally think when hearing weak value map Weak key, strong value = JS's WeakMap Weak key, weak value = my WeakKeyValueMap (what I perceived the proposal to be) Hope this resolves the communicatio…

I stumbled across weak-value - npm when looking for language precedent, and that aligns with my taxonomy as well.

How to implement TwoWayWeakMap? Using WeakRef?

I have questions

trusktr December 31, 2021, 12:29am 15

The problem all of the implementations have motivated me to open this issue:

Topic		Replies	Views
LossyRef, better than WeakRef 💡 Ideas	17	1168	February 22, 2022
Native WeakValueMap 💡 Ideas	12	503	June 17, 2024
Allow weak maps to contain primitives 💡 Ideas	17	555	October 24, 2021
Add enumeration methods (and clear) to WeakMap and WeakSet 💡 Ideas	3	409	December 2, 2020
Weak/Map and Weak/Set `put(key, value): value` anyone? 💡 Ideas proposal	2	143	July 28, 2026

How to implement TwoWayWeakMap? Using WeakRef?

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