This thread from 2011 might help understand why they should not be enumerable (it links to another thread as well inside). https://mail.mozilla.org/pipermail/es-discuss/2011-April/013604.html
On Wed, Jul 13, 2016 at 8:08 AM, Isiah Meadows <[email protected]> wrote: > Could you explain a real world use case for this? I recall some that it > would've simplified some, but the best implementation often didn't even > require iteration, but just changing the data layout altogether. > > On Wed, Jul 13, 2016, 08:13 Michael Kriegel < > [email protected]> wrote: > >> Hi everyone, >> >> not sure, whether this is the right place for discussing a feature >> request - and how to find out, whether this was already >> proposed/discussed before and with which result... My google search did >> not bring up anything about it. >> >> On my opinion it should be made possible to iterate over all elements in >> a WeakSet & WeakMap. I already found many cases, in which I'd like to >> have used the neat feature of "garbage collect the object, if it is not >> referred to by others anymore", but with the necessity to know, which >> objects are in the set (not only, if a given object is). An example: >> >> Registering callbacks to objects: >> >> class Foo { >> onBla(Handler) { >> this.BlaSuperWeakMap.push(Handler); >> } >> >> someOtherMethod() { >> for (let X in this.BlaSuperWeakMap) { >> X(); >> } >> } >> >> constructor() { >> this.BlaSuperWeakMap = new SuperWeakMap(); >> } >> } >> >> const MyFoo = new Foo(); >> { >> let MyHandler1 = function(){ >> console.log('MyHandler1 called'); >> }; >> MyFoo.onBla(MyHandler1); >> console.log('Invokation1:'); >> MyFoo.someOtherMethod(); >> } >> let MyHandler2 = function(){ >> console.log('MyHandler2 called'); >> }; >> MyFoo.onBla(MyHandler2); >> MyFoo.onBla(function(){ >> console.log('MyHandler3 called'); >> }); >> console.log('Invokation2:'); >> MyFoo.someOtherMethod(); >> MyHandler2 = undefined; >> console.log('Invokation3:'); >> MyFoo.someOtherMethod(); >> >> Expected result: >> Invokation1: >> MyHandler1 called >> Invokation2: >> MyHandler2 called >> Invokation3: >> >> Basically the example is: Invoke the callback of all objects which still >> "exist" (in the meaning of having "non-weak" references towards them). >> >> I know this may have some caveats. It would be necessary to check the >> reference count of the object in the SuperWeakSet, because the object >> may have no "non-weak" references left but still was not yet garbage >> collected. I do not know, whether current ECMAScript-Implementations and >> their garbage collecting solutions could handle this easily - basically >> it is the same decision, which the garbage collector would make: If an >> object can be disposed, because it has no non-Weak references pointing >> to it, the object is by definition not in the WeakSet anymore. And >> implementations could in that case even give a hint to the garbage >> collector, which may improve performance of applications, which use the >> SuperWeakSet alot. >> >> Greetings, Michael >> >> >> >> >> >> >> >> >> >> _______________________________________________ >> 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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