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Fix erroneous diffing w/ growing list #4975

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Merged
JoviDeCroock merged 2 commits into from
Dec 16, 2025
+24 −0
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Fix erroneous diffing w/ growing list #4975

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b109450
Fix cause where oldVNode can carry over
JoviDeCroock Dec 16, 2025
ce55fc5
Add test
JoviDeCroock Dec 16, 2025
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1 change: 1 addition & 0 deletions src/diff/children.js
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Original file line number Diff line number Diff line change
Expand Up @@ -235,6 +235,7 @@ function constructNewChildrenArray(
remainingOldChildren
));

oldVNode = NULL;
if (matchingIndex != -1) {
oldVNode = oldChildren[matchingIndex];
remainingOldChildren--;
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23 changes: 23 additions & 0 deletions test/browser/keys.test.js
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Original file line number Diff line number Diff line change
Expand Up @@ -1128,4 +1128,27 @@ describe('keys', () => {
render(<App y="2" />, scratch);
expect(actions).to.deep.equal(['mounted 1', 'mounted 2', 'mounted 3']);
});

// Issue #4973: Test growing list diff
it('should correctly diff a growing list of keyed children', () => {
let values = [0, 1, 2, 3, 4];

render(<List values={values} />, scratch);
expect(scratch.textContent).to.equal('01234');

values = [2, 3, 4, 5, 6];
clearLog();

render(<List values={values} />, scratch);
expect(scratch.textContent).to.equal('23456');

expect(getLog()).to.deep.equal([
'<li>0.remove()',
'<li>1.remove()',
'<li>.appendChild(#text)',
'<ol>234.appendChild(<li>5)',
'<li>.appendChild(#text)',
'<ol>2345.appendChild(<li>6)'
]);
});
});
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