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handle moving nodes #382

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d8f5ca6
handle moving nodes
mdynnl Nov 11, 2024
9161ac3
lower initialization cost
mdynnl Nov 15, 2024
011df9d
refactor test
mdynnl Nov 15, 2024
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17 changes: 13 additions & 4 deletions packages/dom-expressions/src/client.js
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Original file line number Diff line number Diff line change
Expand Up @@ -460,7 +460,6 @@ function insertExpression(parent, value, current, marker, unwrapArray) {
if (value === current) return current;
const t = typeof value,
multi = marker !== undefined;
parent = (multi && current[0] && current[0].parentNode) || parent;
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@mdynnl mdynnl Nov 11, 2024

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Not sure what might break by this removal but this for sure breaks the parent comparison in cleanChildren

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@titoBouzout titoBouzout Nov 12, 2024

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Ryan made a comment about this code in a related issue here #307 (comment)
I will have to study it again to refresh my mind, I'm not sure I actually ever understood that part

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@mdynnl mdynnl Nov 15, 2024

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I've tried to track this down and, oh well 😅, no wonder even Ryan can't remember this. This check existed since the beginning.

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@ryansolid ryansolid Jan 27, 2025

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Yeah someone made a codesandbox that was sorting nodes around randomly on an interval and it would occasionally break. I added that way back. But I think its need predates the "modern" way we handle fragments I changed to back in Feb 2019.

In any case I'm moving forward with this not there right now in 2.0 stuff.


if (t === "string" || t === "number") {
if (hydrating) return current;
Expand Down Expand Up @@ -570,7 +569,14 @@ function appendNodes(parent, array, marker = null) {
for (let i = 0, len = array.length; i < len; i++) parent.insertBefore(array[i], marker);
}

let moved;

function cleanChildren(parent, current, marker, replacement) {
if (!moved) {
moved = new WeakSet();
queueMicrotask(() => (moved = null));
}
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@mdynnl mdynnl Nov 11, 2024

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WeakSet is already used by hydration so doesn't hurt anything but there might be better approaches than this.

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@titoBouzout titoBouzout Nov 12, 2024

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I suggest considering a strong referenced array to be cleared in the microtask as moved.length = 0. As the cost of instantiating could be removed, and also a set will try to deduplicate the nodes

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@mdynnl mdynnl Nov 15, 2024

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I was thinking if weakset was faster than array to check for element existence. Any form of book-keeping works really. We could also keep it in the nodes but I don't know the performance side of this. Essentially we need to know if a node has changed position in the tree.

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@titoBouzout titoBouzout Nov 15, 2024 •
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Makes sense. Last time I measured this, for a fairly low amount of items there was no significant difference between [].includes and set.has and you do not pay the cost of the Set having to deduplicate/hash items. I think solid reactivity does this (ex: reading a signal just pushes to observers without deduplicating).

At first sight sounds like keeping the info in the node will complicate the logic, either a microtask for each node or some sort of counter. Probably worth considering, as a microtask could introduce desync, not sure if solidjs/signals will use microtasks, but everything becomes a race when used. This is why I do not like reactivity in microtasks

Maybe make of the WeakSet a Set to be hold in the parent scope, and call set.clear() in the microtask. I'm thinking of at least not paying the cost of creating the set/array each time.


if (marker === undefined) return (parent.textContent = "");
const node = replacement || document.createTextNode("");
if (current.length) {
Expand All @@ -579,9 +585,12 @@ function cleanChildren(parent, current, marker, replacement) {
const el = current[i];
if (node !== el) {
const isParent = el.parentNode === parent;
if (!inserted && !i)
isParent ? parent.replaceChild(node, el) : parent.insertBefore(node, marker);
else isParent && el.remove();
if (!inserted && !i) {
node.parentNode && moved.add(node);
isParent && !moved.has(el)
? parent.replaceChild(node, el)
: parent.insertBefore(node, marker);
} else isParent && el.remove();
} else inserted = true;
}
} else parent.insertBefore(node, marker);
Expand Down
53 changes: 52 additions & 1 deletion packages/dom-expressions/test/dom/insert.spec.js
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Original file line number Diff line number Diff line change
Expand Up @@ -2,7 +2,7 @@
* @jest-environment jsdom
*/
import * as r from '../../src/client';
import * as S from "s-js";
import S from "s-js";

describe("r.insert", () => {
// <div><!-- insert --></div>
Expand Down Expand Up @@ -355,6 +355,57 @@ describe("r.insert with Markers", () => {
expect(parent.innerHTML).toBe('hello ');
});

it("can move the same node within the same parent", () => {
const toggle = S.data(true);

const el = document.createElement("div");
el.append(",");

const node = document.createElement("span");
node.append("x");

const dispose = root(() => {
r.insert(el, () => !toggle() && node, el.firstChild);
r.insert(el, () => toggle() && node, null);
});

expect(el.textContent).toBe(",x");
toggle(!toggle());
expect(el.textContent).toBe("x,");

dispose();
});

it("can move the same node within different parents", () => {
const toggle = S.data(true);

const a = document.createElement("div");
a.append("a");

const b = document.createElement("div");
b.append("b");

const node = document.createElement("span");
node.append("x");

const dispose = root(() => {
r.insert(a, () => !toggle() && node, a.firstChild);
r.insert(b, () => toggle() && node, b.firstChild);
});

expect(a.textContent).toBe("a");
expect(b.textContent).toBe("xb");
toggle(!toggle());
expect(a.textContent).toBe("xa");
expect(b.textContent).toBe("b");

dispose();
});

function root(fn) {
return S.root(d => (fn(), d));
}

function insert(val) {
const parent = container.cloneNode(true);
r.insert(parent, val, parent.childNodes[1]);
Expand Down
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