Answering the question in the subject line, no. The key is the difference between a standalone proxy and a membrane. With a membrane, the key is that the:
* Countdown class * Countdown.prototype * Countdown.prototype.dec * instances of the Countdown class * the WeakMaps used by the Countdown class to store it private state (_counter, _action) are all on one side of the membrane. As is conventional, let's call that the wet side, and the other side the dry side. Say both a Countdown instance c and the WeakMap _action get passed through the membrane. Let's name the corresponding dry proxies dry_c and dry_action. If, on the dry side, someone does dry_action.get(dry_c) then this would trap on dry_action, passing dry_c back through the membrane, resulting in the dry_action handler performing, on the wet side const r = _action.get(c) The wet result, r, of this invocation would get passed back through the membrane, leading to the original expression returning dry_r. Alternatively, let's say that someone on the dry side does dry_c.dec() This traps on dry_c, which looks up c's inherited "dec" method, passes that back through the membrane, resulting in a dry_dec proxy for that method. When that is invoked with dry_c as its this, it traps, invoking the wet dec method with c as its this. Conclusion: it all works fine. On Sat, Nov 21, 2015 at 3:02 PM, Axel Rauschmayer <rausc...@icloud.com> wrote: > Take, for example, the following class, which uses WeakMaps for its > private data: > > ```js > let _counter = new WeakMap(); > let _action = new WeakMap(); > class Countdown { > constructor(counter, action) { > _counter.set(this, counter); > _action.set(this, action); > } > dec() { > let counter = _counter.get(this); > if (counter < 1) return; > counter--; > _counter.set(this, counter); > if (counter === 0) { > _action.get(this)(); > } > } > } > ``` > > If you wrap an instance of `Countdown` with a revocable Proxy (e.g. when > it is returned by a method inside a membrane) that resets its private > state, because its `this` changes. > > Right? If yes then I’d expect that to cause problems for code that uses > WeakMaps for private data. > > -- > Dr. Axel Rauschmayer > a...@rauschma.de > rauschma.de > > > > _______________________________________________ > es-discuss mailing list > es-discuss@mozilla.org > https://mail.mozilla.org/listinfo/es-discuss > -- Cheers, --MarkM
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