Skip to content

Port #4888 to v10 #4890

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 2 commits into from
Aug 17, 2025
Merged

Port #4888 to v10 #4890

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
f980b8e
Do not re-insert memoized vnodes that keep their relative order after…
vasylenkoval Aug 14, 2025
784d90c
rename shouldSkipDomUpdate to shouldPlace and hoist INSERT_VNODE flag…
vasylenkoval Aug 16, 2025
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
21 changes: 11 additions & 10 deletions src/diff/children.js
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -124,11 +124,9 @@ export function diffChildren(
firstChildDom = newDom;
}

if (
childVNode._flags & INSERT_VNODE ||
oldVNode._children === childVNode._children
) {
oldDom = insert(childVNode, oldDom, parentDom);
let shouldPlace = !!(childVNode._flags & INSERT_VNODE);
if (shouldPlace || oldVNode._children === childVNode._children) {
oldDom = insert(childVNode, oldDom, parentDom, shouldPlace);
} else if (typeof childVNode.type == 'function' && result !== UNDEFINED) {
oldDom = result;
} else if (newDom) {
Expand Down Expand Up @@ -338,9 +336,10 @@ function constructNewChildrenArray(
* @param {VNode} parentVNode
* @param {PreactElement} oldDom
* @param {PreactElement} parentDom
* @param {boolean} shouldPlace
* @returns {PreactElement}
*/
function insert(parentVNode, oldDom, parentDom) {
function insert(parentVNode, oldDom, parentDom, shouldPlace) {
// Note: VNodes in nested suspended trees may be missing _children.

if (typeof parentVNode.type == 'function') {
Expand All @@ -352,16 +351,18 @@ function insert(parentVNode, oldDom, parentDom) {
// children's _parent pointer to point to the newVNode (parentVNode
// here).
children[i]._parent = parentVNode;
oldDom = insert(children[i], oldDom, parentDom);
oldDom = insert(children[i], oldDom, parentDom, shouldPlace);
}
}

return oldDom;
} else if (parentVNode._dom != oldDom) {
if (oldDom && parentVNode.type && !parentDom.contains(oldDom)) {
Copy link
Contributor Author

@vasylenkoval vasylenkoval Aug 17, 2025 •
edited
Loading

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

The ported code diff also happens to contain one more improvement that replaces the parentDom.contains(...) check with !oldDom.parentNode. Original PR: #4666. Please let me know if you don't want to include it here.

Copy link
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Should be fine I think, test suite passes anyhow. And thanks for tracking down the blame there, saves me from doing it myself

oldDom = getDomSibling(parentVNode);
if (shouldPlace) {
if (oldDom && parentVNode.type && !oldDom.parentNode) {
oldDom = getDomSibling(parentVNode);
}
parentDom.insertBefore(parentVNode._dom, oldDom || NULL);
}
parentDom.insertBefore(parentVNode._dom, oldDom || NULL);
oldDom = parentVNode._dom;
}

Expand Down
59 changes: 58 additions & 1 deletion test/browser/lifecycles/shouldComponentUpdate.test.js
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -2,7 +2,7 @@ import { setupRerender } from 'preact/test-utils';
import { createElement, render, Component, Fragment } from 'preact';
import { vi } from 'vitest';
import { setupScratch, teardown } from '../../_util/helpers';
import { logCall, clearLog } from '../../_util/logCall';
import { logCall, getLog, clearLog } from '../../_util/logCall';

/** @jsx createElement */

Expand Down Expand Up @@ -962,4 +962,61 @@ describe('Lifecycle methods', () => {
`<div>Before</div><div>Component</div><div>After</div>`
);
});

it('should not re-insert memoized items that keep their relative order after swap', () => {
class MemoizedItem extends Component {
shouldComponentUpdate(nextProps) {
return nextProps.value !== this.props.value;
}
render() {
return <div>{this.props.value}</div>;
}
}

const App = ({ items }) => (
<div>
{items.map(value => (
<MemoizedItem key={value} value={value} />
))}
</div>
);

render(<App items={[1, 2, 3, 4, 5, 6, 7]} />, scratch);

function renderItemsAndAssert({ items, expectedLog }) {
clearLog();
render(<App items={items} />, scratch);
expect(scratch.innerHTML).to.equal(
`<div>${items.map(value => `<div>${value}</div>`).join('')}</div>`
);
expect(getLog()).to.deep.equal(expectedLog);
}

// Swap 1 and 7
renderItemsAndAssert({
items: [7, 2, 3, 4, 5, 6, 1],
expectedLog: [
'<div>1234567.insertBefore(<div>7, <div>1)',
'<div>7123456.appendChild(<div>1)'
]
});

// Swap 2 and 6
renderItemsAndAssert({
items: [7, 6, 3, 4, 5, 2, 1],
expectedLog: [
'<div>7234561.insertBefore(<div>6, <div>2)',
'<div>7623451.insertBefore(<div>2, <div>1)'
]
});

// Swap 3 and 5
renderItemsAndAssert({
items: [7, 6, 5, 4, 3, 2, 1],
expectedLog: [
'<div>7634521.insertBefore(<div>5, <div>3)',
'<div>7653421.insertBefore(<div>3, <div>2)'
]
});
});
});
Loading