`WeakMap` holds the *key* weakly, not the value - it holds the value strongly. If you have the key such that you can use it to get at the value, you'll always have the value.
`WeakRef` is a container around a weakly held *value*, which I don't believe is possible to fully polyfill, even with `WeakMap`/`WeakSet` (because they are not enumerable). On Sun, Sep 27, 2015 at 9:09 AM, Herby Vojčík <[email protected]> wrote: > A naive question: don't you get working weakref by using a WeakMap and > getting and setting using the same key? A naive point of view suggests > that. What am I not seeing here? > > Herby > > Isiah Meadows wrote: > >> I'm resurrecting this [1] because I have found a use case where I needed >> a weak reference. Is there any chance this could get into the language? >> >> Here's my particular use case: making a stream with a rotating >> destination that itself acts as a stream (snippet of that code, or what >> I'd like it to be). >> >> ```js >> function rotateStream(interval, format) { >> // Without the weak reference here, there's a memory leak >> const ref = new WeakReference({}) >> setStream(ref.get(), format) >> setInterval(function () { >> if (ref.exists()) setStream(ref.get(), format) >> else clearInterval(this) >> }, interval) >> return ref.get() >> } >> ``` >> >> This basically rotates an active stream, with the weak reference >> pointing to the said stream. The alternative requires explicit marking >> (in this case, with a `close` method): >> >> ```js >> function leakyRotateStream(interval, format) { >> let stream = {close() { >> clearInterval(timer) >> timer = stream = null >> }} >> const timer = setInterval(function () { >> setStream(stream, format) >> }, interval) >> setStream(stream, format) >> return stream >> } >> ``` >> >> In this use case, weak references would simplify the implementation and >> reduce memory costs. And I would rather take advantage of the GC >> machinery than explicit memory management (as explicit as C), as it >> would be easier to collect when that's the only thing referenced. >> >> (The setInterval callback is gc'd with all its references when it's >> cleared from within.) >> >> Thankfully, I'm using Node.js, so `weak` [2] is an option (the only >> option, really). But I would definitely appreciate if it was available >> in JS proper, across engines. V8, SpiderMonkey, and JSC all have weak >> references to JS objects as part of their public API, and I would be >> surprised if the implementation work would be anything significant. >> >> [1]: https://esdiscuss.org/topic/what-is-the-status-of-weak-references >> [2]: https://github.com/TooTallNate/node-weak >> >> -- >> Isiah Meadows >> >> _______________________________________________ >> es-discuss mailing list >> [email protected] >> https://mail.mozilla.org/listinfo/es-discuss >> > _______________________________________________ > es-discuss mailing list > [email protected] > https://mail.mozilla.org/listinfo/es-discuss >
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