useMemo not explained in Tutorial

[MightyPork]

The Context part of the tutorial uses the useMemo() hook, but there's no explanation what this does and how it's used.

Later you are asked to use it yourself when solving the exercise. I still didn't understand what it does, even after reading the solution.

[JoviDeCroock]

That's valuable feedback thank you! useMemo returns a stable reference for a given value, so it can be used to run expensive computations, .... and only re-calculate when the dependencies contained within the second argument (the array) change.

[Antarian]

I understand useMemo is used for expensive computations, but somehow failing to understand why in tutorial user or increment are defined as expensive computations?
Is it just random example to show useMemo hook?

[rschristian]

As Jovi mentions, memoization isn't exclusively for expensive computations, it can also used to create stable references. Without memoizing in that example, each render of <App /> would create a new auth object thereby triggering the context in all consumers even if the inner values (user and setUser) haven't changed.

It might not be the best example (contributions welcome & appreciated!) but it does serve a purpose, it's not "random".

[Antarian]

Thank you for explanation. It makes more sense to me now.
I have also checked React site for useMemo. There are more possible use cases. It's more that I am starting with Preact without a knowledge of React.

[rschristian]

Fully agree, we could do with fleshing out our hooks docs in general, it's all super light on details, examples, etc.

Will go on my to-do!