Prevent Reaction From Keeping a Reference to The OldValue

[barroij]

HI Folks

This PR is about reaction and memory retainment preventing object beeing garbage collected

For some reason, the reactionRunner of a reaction creates a closure around an oldValue and so the reference to the oldValue is kept untill a newValue is computed.

I can see no reason for keeping such a reference "alive", oldValue could just be declared in the scope of the reactionRunner as it is the only place where it is used. Doing so, the oldValue can be garbage collected if needed.

No additional Unit test is needed for such a change, and there is no backward compatibility issue as it only touches internal/private stuff within a reaction.

[changeset-bot]

🦋 Changeset detected

Latest commit: a3d5692

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

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mobx	Patch

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[urugator]

Did you investigate the behavior when expression throws?

[barroij]

@urugator
Assuming that disableErrorBoundaries is false or that an onError errorHandler is provided, if expression thows an exception it would be caught within track, but changed remains unchanged anyway, its value is false. So the effectAction is not called.
Except if (firstTime && opts.fireImmediately!) is true but in this case oldValue is undefined as it used to be, so the behavior remains the same.

[urugator]

Ok, thank you. Could you please provide changeset (yarn changeset)? Otherwise LGTM.

[barroij]

I never made a changeset before. I ran yarn changeset and commited the generated .md file, is that all ?

[urugator]

Yep. Github just seems to be sluggish atm, at least on mind end.