Are ES Modules garbage collected? If so, do they re-execute on next import?

Andrea Giammarchi andrea.giammarchi at gmail.com
Wed Jul 1 06:57:26 UTC 2020


even if dereferenced, a dynamic import could re-reference it any time, and
I would expect it to still be the same module, it'd be a surprise otherwise
(cached things, same namespace checks, etc).

On Wed, Jul 1, 2020 at 7:33 AM Isiah Meadows <contact at isiahmeadows.com>
wrote:

> Just to expand on that, if the module record itself is dereferenced
> (like if it's evicted from the cache somehow), then yes, it should be
> collected as appropriate. However, I'm not aware of any major
> implementation that offers that functionality.
>
> -----
>
> Isiah Meadows
> contact at isiahmeadows.com
> www.isiahmeadows.com
>
> On Tue, Jun 30, 2020 at 6:22 PM Gus Caplan <me at gus.host> wrote:
> >
> > Modules in the spec are cached by specifier by modules that import them.
> Modules in major implementations are additionally cached for the entire
> realm by absolute URLs. I would say that for actual code (functions and
> classes and whatnot) leaks aren't really a problem. Even if you import a
> ton of levels, that's not that much memory. The main concern I've seen
> raised is JSON modules, where once you import them the JSON object, which
> can be quite large, will never be collected. Of course, there is a simple
> solution to that (fetch) so it isn't a world ending problem.
> >
> > On Tue, Jun 30, 2020 at 7:41 PM #!/JoePea <joe at trusktr.io> wrote:
> >>
> >> I am curious: can modules be garbage collected if the exports are not
> >> references by anything anymore? And if so, will the module be
> >> re-evaluated the next time it is imported?
> >>
> >> I haven't tried an experiment to answer this yet. I'll be back to post
> >> findings if someone doesn't post an official answer first.
> >>
> >> I'm thinking about code longevity. For example, if we make
> >> long-running web-based applications with many routes and features (for
> >> sake of example imagine a desktop environment, or a MMORPG game, with
> >> apps or components that are loaded within the same context). Over
> >> time, if imports are not collected, then it means we have a memory
> >> leak.
> >>
> >> Imagine, for example, an infinite-universe MMORPG where you can land
> >> on different planets where the code for features of a planet are
> >> provided by third parties as ES Modules. I know, this might not be a
> >> safe idea to import any code into an app, but just imagine it for sake
> >> of example (imagine we have a continuous integration system to test
> >> and verify code security, or something, before that code is allowed to
> >> be consumed in the app). Imagine you play this app for many many days,
> >> and visit many places, and you leave the app running the whole time
> >> (because farming for resources is disabled if the app is not running,
> >> or something).
> >>
> >> I would imagine that we want unused modules (when we leave a planet,
> >> for example) to be (destroyed) garbage collected so that we don't
> >> waste memory.
> >>
> >> #!/JoePea
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