![]() You can read the full explanation for these limitations in the proposal. Further, this feature is not meant to be relied upon for normal operation, but rather as a debugging aid and as a backstop against certain types of bugs. This finalizer is called after the object has already been destroyed and you have to predetermine what part of the instance data needs to be passed to the finalizer for it to do its work. If you read the proposal thoroughly, you will see that it's nothing like a full-blown destructor in a language like C++. If the object is garbage collected (because no other code still has a reference to it), then this finalizer scheme allows one to at least put a message to the console that an external resource has just been leaked and code elsewhere should be fixed to prevent this leak. There is a Stage 3 EMCAScript proposal to add a user-defined finalizer function after an object is garbage collected.Ī canonical example of something that would benefit from a feature like this is an object that contains a handle to an open file. I found it useful to see the distinction between the three.Įdit in 2020 - proposal for object finalizer ![]() This discussion covers finalizer, destructor and disposer design patterns. I suppose there's a possible weakListener() that would not prevent garbage collection, but such a thing does not exist either.įYI, here's another relevant question Why is the object destructor paradigm in garbage collected languages pervasively absent?. And, once you've removed the event listeners, there's no need for the destructor for this purpose. They just disappear from the weakMap or weakSet at some point (when they are GCed).įYI, the issue with this type of destructor you ask for (and probably why there isn't much of a call for it) is that because of garbage collection, an item is not eligible for garbage collection when it has an open event handler against a live object so even if there was such a destructor, it would never get called in your circumstance until you actually removed the event listeners. If, at the same time you also make sure there are no other references to that object, then your object will become eligible for garbage collection at that point.ĮS6 does have weakMap and weakSet which are ways of keeping track of a set of objects that are still alive without affecting when they can be garbage collected, but it does not provide any sort of notification when they are garbage collected. You will have to call it manually at the appropriate time. The idea is that you're telling the object to disconnect itself from anything else it is hooked up to (deregister event listeners, clear external object references, etc.). You can call the method something like release() or deregister() or unhook() or anything of that ilk. If you want to tell your object that you are now done with it and it should specifically release any event listeners it has, then you can just create an ordinary method for doing that. But what would be a good convention if ECMAScriptĭoesn't have destructors? Should I create a method called destructorĪnd call it manually when I'm done with the object? Any other idea? It can be very handy to have a function that tests for an object being an instance of a particular class.I just came across this question in a search about destructors and I thought there was an unanswered part of your question in your comments, so I thought I would address that. It’s doesn’t “just work,” but it can make certain things possible (like decorating constructors) that are otherwise even more awkward to implement. ![]() Is that what you want? Who knows!? This isn’t a justification for the pattern, as much as an explanation that it is a useful, but leaky abstraction. Now it works, but of course snafu is an instance of Fubar, not of LoggingFubar. concatenated () //=> 'Situation Normal All Fsked Up' Function Fubar ( foo, bar ) var LoggingFubar = logsArguments ( Fubar ) var snafu = new LoggingFubar ( " Situation Normal ", " All Fsked Up " ) //=> Situation Normal All Fsked Up snafu.
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