Dependency leakage between HTML attributes (=Extra dependencies causing unnecessary re-runs)

[nns2009]

Describe the bug

I found that classList (and possibly other HTML attributes) causes unnecessary re-runs. In the following code, createEffect only reruns when v() changes (I manually examined w.vs). Similarly, HTML text re-runs only when v() changes (I only get one render for ${i} for the element, which was updated. Yet, every single change of any element (values()[i]) I get classList for ${i} for every single element in values(). This is totally unexpected, especially considering that classList and HTML renders are right next to each other.

import { createEffect, createMemo, createSignal, Index } from "solid-js";

export default function ClassListRerunExperiment() {
	const names = createMemo(() => ['one', 'two', 'three', 'four', 'five', 'six', 'seven']);
	const [values, setValues] = createSignal([1, 2, 3, 4, 5, 6, 7]);

	function setOneValue(i: number, v: number) {
		const next = [...values()];
		next[i] = v;
		setValues(next);
	}

	return <Index each={names()}>{(t, i) => {
		console.log('Row render:', i);
		const v = createMemo(() => values()[i]);

		createEffect(() => {
			if (i !== 0) return;
			const w = window as any;
			w.vs = w.vs ?? [];
			w.vs.push(v());
		});

		return <div classList={{
			'big': (console.log(`classList for ${i}`), v() >= 5),
		}}>
			{(console.log(`render for ${i}`), v(), 'z')}
			<button onClick={() => setOneValue(i, v() - 1)}>-</button>
			{v()}
			<button onClick={() => setOneValue(i, v() + 1)}>+</button>
			<button disabled={values()[i] <= 2}>Low</button>
			{values().join(',')} {values()[i]}
		</div>
	}}</Index>;
}

I was able to track down the problem to this specific line:

<button disabled={values()[i] <= 2}>Low</button>

With this specific line removed, reactivity works as expected, any '-'/'+' press only results in a single classList for ${i} log. Somehow, using values() in 'disabled' attribute (maybe also any other HTML attribute?) seems to leak values() as a dependency of classList. At the same time, using values() for rendering:

{values().join(',')}

does not cause any leakage.

Your Example Website or App

https://stackblitz.com/edit/solidjs-dependency-leakage-zqkzgank?file=src%2FApp.tsx

Steps to Reproduce the Bug or Issue

Open the link, open DevTools console.
Click any of the '-' or '+' buttons.

Expected behavior

Only one classList for ${i} is logged exactly for the element being updated

Screenshots or Videos

No response

Platform

• OS: Windows, also Stackblitz, most likely cross-platform
• Browser: Edge, Opera, Yandex Browser
• Version: All latest

Additional context

No response

[dennev]

This isn't a bug; signal() can't just fetch a part of a nested internal structure. If you want a responsive element for more complex structures, createStore will help.

In the example createMemo, when binding to readSignal, I suspect that the memo is referring to the address with the final destination value, not the array itself, so it should work as you intended.

[nns2009]

Thanks for the reply.
I was explained in the SolidJS Discord that this attribute behavior is a deliberate trade-off made for optimization.
Still, if that is the case, it goes against the core "fine-grained reactivity" promise, so I think it would be worth to document/explain it.
In general, a page with all the pitfalls/issues/workarounds/patterns/anti-patterns would be super helpful.

[titoBouzout]

Thanks, this is duplicate of #2142

I have asked where to document this and similar behaviours, and are in the process of doing so. Here is a condensed explanation

Solid uses 1 effect to update at the same time, all of the props/atttributes of native elements contained in a component. Everything is cached in local vars and compared with the previous value. The assumption is that props/attrs are deterministic, and only change because some tracked value changed. Therefore, functions that aren't deterministic should be memoized, and non-deterministic objects should be hoisted, to avoid values unexpectedly being changed.

[nns2009]

Nice to hear it will get documented!
I think one mid-large page with all Solid quirks should be possible.
There are hopefully limited number of those, but the information on even basic topics so far is very lacking.
I just spent 6+ hours on "computations created outside a createRoot or render will never be disposed" 😵 (and couldn't solve it)