Strict Mode: Document behavior of setState callbacks

[fefrei]

As per the documentation, Strict Mode has three effects:

• Your components will re-render an extra time to find bugs caused by impure rendering.
• Your components will re-run Effects an extra time to find bugs caused by missing Effect cleanup.
• Your components will be checked for usage of deprecated APIs.

As per his issue comment, “setState updaters will run twice in strict mode in development”. I think this behavior should be documented on the Strict Mode page.

[rickhanlonii]

Yes, this is documented on that same page here and in the docs for setState here.

[fefrei]

I see, looks like I overread them, thanks. There might still be room for improvement, though: The list I quoted above is titled “Strict Mode enables the following development-only behaviors”, making it sound (to me) like it's an exhaustive lists of what strict mode does. This is what confused me – I saw some weird behavior due to a bug in my code, wondered whether this might be triggered do to the setState updater being run twice, saw the (exhaustive‽) list above, and discarded that theory. Maybe this list can be completed, or re-worded as just an example of the types of changes strict mode enables?