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Experiment: add moveBefore rather than insertBefor when available #4938

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249a599
Experiment: add moveBefore rather than insertBefor when available
JoviDeCroock Oct 24, 2025
3b083af
Add try block
JoviDeCroock Oct 24, 2025
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3 changes: 3 additions & 0 deletions src/constants.js
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Original file line number Diff line number Diff line change
Expand Up @@ -33,3 +33,6 @@ export const EMPTY_OBJ = /** @type {any} */ ({});
export const EMPTY_ARR = [];

export const MATHML_TOKEN_ELEMENTS = /(mi|mn|mo|ms$|mte|msp)/;

export const HAS_MOVE_BEFORE_SUPPORT =
typeof window !== 'undefined' && 'moveBefore' in Element.prototype;
27 changes: 22 additions & 5 deletions src/diff/children.js
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Original file line number Diff line number Diff line change
Expand Up @@ -6,7 +6,8 @@ import {
INSERT_VNODE,
MATCHED,
UNDEFINED,
NULL
NULL,
HAS_MOVE_BEFORE_SUPPORT
} from '../constants';
import { isArray } from '../util';
import { getDomSibling } from '../component';
Expand Down Expand Up @@ -129,8 +130,9 @@ export function diffChildren(
}

let shouldPlace = childVNode._flags & INSERT_VNODE;
const isMounting = oldVNode == NULL || oldVNode._original == NULL;
if (shouldPlace || oldVNode._children === childVNode._children) {
oldDom = insert(childVNode, oldDom, parentDom, shouldPlace);
oldDom = insert(childVNode, oldDom, parentDom, shouldPlace, isMounting);
} else if (typeof childVNode.type == 'function' && result !== UNDEFINED) {
oldDom = result;
} else if (newDom) {
Expand Down Expand Up @@ -339,9 +341,10 @@ function constructNewChildrenArray(
* @param {PreactElement} oldDom
* @param {PreactElement} parentDom
* @param {number} shouldPlace
* @param {boolean} isMounting
* @returns {PreactElement}
*/
function insert(parentVNode, oldDom, parentDom, shouldPlace) {
function insert(parentVNode, oldDom, parentDom, shouldPlace, isMounting) {
// Note: VNodes in nested suspended trees may be missing _children.
if (typeof parentVNode.type == 'function') {
let children = parentVNode._children;
Expand All @@ -352,7 +355,7 @@ function insert(parentVNode, oldDom, parentDom, shouldPlace) {
// children's _parent pointer to point to the newVNode (parentVNode
// here).
children[i]._parent = parentVNode;
oldDom = insert(children[i], oldDom, parentDom, shouldPlace);
oldDom = insert(children[i], oldDom, parentDom, shouldPlace, false);
}
}

Expand All @@ -362,7 +365,21 @@ function insert(parentVNode, oldDom, parentDom, shouldPlace) {
if (oldDom && parentVNode.type && !oldDom.parentNode) {
oldDom = getDomSibling(parentVNode);
}
parentDom.insertBefore(parentVNode._dom, oldDom || NULL);

const target = oldDom || NULL;
if (HAS_MOVE_BEFORE_SUPPORT && !isMounting) {
try {
// Technically this can throw in multiple scenario's one of which
// is a component that is mounting - we could consider removing
// the condition because we have a catch in place.
// @ts-expect-error This isn't added to TypeScript lib.d.ts yet
parentDom.moveBefore(parentVNode._dom, target);
} catch (error) {
parentDom.insertBefore(parentVNode._dom, target);
}
} else {
parentDom.insertBefore(parentVNode._dom, target);
}
}
oldDom = parentVNode._dom;
}
Expand Down
8 changes: 8 additions & 0 deletions test/_util/logCall.js
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Original file line number Diff line number Diff line change
Expand Up @@ -39,6 +39,14 @@ export function logCall(obj, method) {
}
break;
}
case 'moveBefore': {
if (args[1] === null && args.length === 2) {
operation = `${serialize(this)}.appendChild(${serialize(args[0])})`;
} else {
operation = `${serialize(this)}.insertBefore(${c})`;
}
break;
}
default: {
operation = `${serialize(this)}.${String(method)}(${c})`;
break;
Expand Down
116 changes: 64 additions & 52 deletions test/browser/focus.test.jsx
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,9 @@

/* eslint-disable react/jsx-boolean-value */

const supportsMove = 'moveBefore' in Element.prototype;
console.log('SUPPORTS MOVE BEFORE:', supportsMove);

describe('focus', () => {
/** @type {HTMLDivElement} */
let scratch;
Expand Down Expand Up @@ -149,34 +152,39 @@
beforeEach(() => {
scratch = setupScratch();
rerender = setupRerender();
});

Check failure on line 155 in test/browser/focus.test.jsx

View workflow job for this annotation

GitHub Actions / Build & Test / Build & Test

test/browser/focus.test.jsx > focus > should maintain focus when swapping elements 

AssertionError: expected +0 to equal 2

- Expected
+ Received

- 2
+ 0

 ❯ validateFocus test/browser/focus.test.jsx:155:2
 ❯ test/browser/focus.test.jsx:186:2

afterEach(() => {
teardown(scratch);
});

it.skip('should maintain focus when swapping elements', () => {
render(
<List>
<Input />
<ListItem>fooo</ListItem>
</List>,
scratch
);
(supportsMove ? it : it.skip)(
'should maintain focus when swapping elements',
() => {
render(
<List>
<Input />
<ListItem>fooo</ListItem>
</List>,
scratch
);

const input = focusInput();
expect(scratch.innerHTML).to.equal(getListHtml([], ['fooo']));
const input = focusInput();
expect(scratch.innerHTML).to.equal(getListHtml([], ['fooo']));

render(
<List>
<ListItem>fooo</ListItem>
<Input />
</List>,
scratch
);
validateFocus(input);
expect(scratch.innerHTML).to.equal(getListHtml(['fooo'], []));
});
render(
<List>
<ListItem>fooo</ListItem>
<Input />
</List>,
scratch
);

expect(scratch.innerHTML).to.equal(getListHtml(['fooo'], []));
// TODO: looks like currently the selection isn't retained when moving
validateFocus(input);
}
);

it('should maintain focus when moving the input around', () => {
function App({ showFirst, showLast }) {
Expand Down Expand Up @@ -470,23 +478,25 @@
return (
<div>
<h1>Heading</h1>
{!this.state.active
? <Fragment>
foobar
<Fragment>
Hello World
<h2>yo</h2>
</Fragment>
<input type="text" ref={i => (input = i)} />
{!this.state.active ? (
<Fragment>
foobar
<Fragment>
Hello World
<h2>yo</h2>
</Fragment>
<input type="text" ref={i => (input = i)} />
</Fragment>
) : (
<Fragment>
<Fragment>
Hello World
<h2>yo</h2>
</Fragment>
: <Fragment>
<Fragment>
Hello World
<h2>yo</h2>
</Fragment>
foobar
<input type="text" ref={i => (input = i)} />
</Fragment>}
foobar
<input type="text" ref={i => (input = i)} />
</Fragment>
)}
</div>
);
}
Expand Down Expand Up @@ -524,23 +534,25 @@
return (
<div>
<h1>Heading</h1>
{!this.state.active
? <Fragment>
foobar
<Fragment>
Hello World
<h2>yo</h2>
</Fragment>
<input type="text" ref={i => (input = i)} value="foobar" />
{!this.state.active ? (
<Fragment>
foobar
<Fragment>
Hello World
<h2>yo</h2>
</Fragment>
<input type="text" ref={i => (input = i)} value="foobar" />
</Fragment>
) : (
<Fragment>
<Fragment>
Hello World
<h2>yo</h2>
</Fragment>
: <Fragment>
<Fragment>
Hello World
<h2>yo</h2>
</Fragment>
foobar
<input type="text" ref={i => (input = i)} value="foobar" />
</Fragment>}
foobar
<input type="text" ref={i => (input = i)} value="foobar" />
</Fragment>
)}
</div>
);
}
Expand Down
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