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Comment by nolanl | Hacker News Reader

Author here. Thanks for the thoughtful reply!

I did indeed mix up `useMemo` and `React.memo` – fixed it in the post.

You're right, I am skipping a lot of details (hence "to grossly oversimplify"). I know that React doesn't invalidate the whole tree, but it does in the worst case. Maybe I should add a note about that.

Svelte not being truly reactive makes perfect sense, but in Svelte v5 my understanding is that "runes mode" does exactly that. This is what I mean by "moving in that direction."

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Hard to ride the line between clear, concise explanation and perfect technical correctness; I thought you picked good tradeoffs in your article.

Appreciate the response! You're right on Svelte v5; I just confirmed that Svelte's new runes are indeed reactive:

    let count = $state(0);
    
    function increment() {
      count += 1;
      console.log(count + " + 1 = " + countPlusOne);  // prints "1 + 1 = 2"
     }

    let countPlusOne = $derived(count + 1);

I never used svelte, so it’s probably a weird question, but how is increment() called?

The calling location has been omitted from the snippet. You don't need to do anything special to call it, just `increment()` wherever it's in scope.

`<button on:click={() => increment()}>+</button>`

could you explain why this demonstrates svelte is reactive?

What's the definition of reactive is I think my question and having a clear demo is useful - if I understood it it looks a useful piece code

> I know that React doesn't invalidate the whole tree, but it does in the worst case

You mean *invalidate the whole subtree, right?

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