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Merged
JoviDeCroock merged 5 commits into from
Feb 21, 2025
Merged

Keyed nullish placeholders cause re-mounts #4700

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e548739
Should handle swapping insertion
JoviDeCroock Feb 20, 2025
ab1d420
Optimize further
JoviDeCroock Feb 20, 2025
9f448ae
Handle more edge cases
JoviDeCroock Feb 20, 2025
01b42a9
Correctness
JoviDeCroock Feb 20, 2025
725f2d2
Add explanatory comment
JoviDeCroock Feb 21, 2025
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22 changes: 20 additions & 2 deletions src/diff/children.js
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Original file line number Diff line number Diff line change
Expand Up @@ -253,7 +253,25 @@ function constructNewChildrenArray(

if (isMounting) {
if (matchingIndex == -1) {
skew--;
// When the array of children is growing we need to decrease the skew
// as we are adding a new element to the array.
// Example:
// [1, 2, 3] --> [0, 1, 2, 3]
// oldChildren newChildren
//
// The new element is at index 0, so our skew is 0,
// we need to decrease the skew as we are adding a new element.
// The decrease will cause us to compare the element at position 1
// with value 1 with the element at position 0 with value 0.
//
// A linear concept is applied when the array is shrinking,
// if the length is unchanged we can assume that no skew
// changes are needed.
if (newChildrenLength > oldChildrenLength) {
skew--;
} else if (newChildrenLength < oldChildrenLength) {
skew++;
}
}

// If we are mounting a DOM VNode, mark it for insertion
Expand Down Expand Up @@ -407,7 +425,7 @@ function findMatchingIndex(
(oldVNode != NULL && (oldVNode._flags & MATCHED) == 0 ? 1 : 0);

if (
oldVNode === NULL ||
(oldVNode === NULL && childVNode.key == null) ||
(oldVNode &&
key == oldVNode.key &&
type === oldVNode.type &&
Expand Down
181 changes: 181 additions & 0 deletions test/browser/keys.test.js
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Original file line number Diff line number Diff line change
Expand Up @@ -943,4 +943,185 @@ describe('keys', () => {

expect(scratch.innerHTML).to.eq(`<div>${expected(sorted)}</div>`);
});

it('should handle keyed replacements', () => {
const actions = [];
class Comp extends Component {
componentDidMount() {
actions.push('mounted ' + this.props.i);
}
render() {
return <div>Hello</div>;
}
}

const App = props => {
return (
<div>
<Comp key={props.y} i={1} />
{false}
<Comp i={2} />
<Comp i={3} />
</div>
);
};

render(<App y="1" />, scratch);
expect(actions).to.deep.equal(['mounted 1', 'mounted 2', 'mounted 3']);

render(<App y="2" />, scratch);
expect(actions).to.deep.equal([
'mounted 1',
'mounted 2',
'mounted 3',
'mounted 1'
]);
});

it('should handle hole prepend', () => {
const actions = [];
class Comp extends Component {
componentDidMount() {
actions.push('mounted ' + this.props.i);
}
render() {
return <div>Hello</div>;
}
}

const App = props => {
return props.y === '2' ? (
<div>
<Comp key={1} i={1} />
<Comp key={2} i={2} />
<Comp key={3} i={3} />
</div>
) : (
<div>
{null}
<Comp key={1} i={1} />
<Comp key={2} i={2} />
<Comp key={3} i={3} />
</div>
);
};

render(<App y="1" />, scratch);
expect(actions).to.deep.equal(['mounted 1', 'mounted 2', 'mounted 3']);

render(<App y="2" />, scratch);
expect(actions).to.deep.equal(['mounted 1', 'mounted 2', 'mounted 3']);
});

it('should handle hole replace', () => {
const actions = [];
class Comp extends Component {
componentDidMount() {
actions.push('mounted ' + this.props.i);
}
render() {
return <div>Hello</div>;
}
}

const App = props => {
return props.y === '1' ? (
<div>
<Comp key={1} i={1} />
<Comp key={2} i={2} />
<Comp key={3} i={3} />
</div>
) : (
<div>
<Comp key={1} i={1} />
{null}
<Comp key={3} i={3} />
</div>
);
};

render(<App y="1" />, scratch);
expect(actions).to.deep.equal(['mounted 1', 'mounted 2', 'mounted 3']);

render(<App y="2" />, scratch);
expect(actions).to.deep.equal(['mounted 1', 'mounted 2', 'mounted 3']);

render(<App y="1" />, scratch);
expect(actions).to.deep.equal([
'mounted 1',
'mounted 2',
'mounted 3',
'mounted 2'
]);
});

it('should handle hole insert', () => {
const actions = [];
class Comp extends Component {
componentDidMount() {
actions.push('mounted ' + this.props.i);
}
render() {
return <div>Hello</div>;
}
}

const App = props => {
return props.y === '2' ? (
<div>
<Comp key={1} i={1} />
<Comp key={2} i={2} />
<Comp key={3} i={3} />
</div>
) : (
<div>
<Comp key={1} i={1} />
<Comp key={2} i={2} />
{null}
<Comp key={3} i={3} />
</div>
);
};

render(<App y="1" />, scratch);
expect(actions).to.deep.equal(['mounted 1', 'mounted 2', 'mounted 3']);

render(<App y="2" />, scratch);
expect(actions).to.deep.equal(['mounted 1', 'mounted 2', 'mounted 3']);
});

it('should handle hole apppend', () => {
const actions = [];
class Comp extends Component {
componentDidMount() {
actions.push('mounted ' + this.props.i);
}
render() {
return <div>Hello</div>;
}
}

const App = props => {
return props.y === '2' ? (
<div>
<Comp key={1} i={1} />
<Comp key={2} i={2} />
<Comp key={3} i={3} />
</div>
) : (
<div>
<Comp key={1} i={1} />
<Comp key={2} i={2} />
<Comp key={3} i={3} />
{null}
</div>
);
};

render(<App y="1" />, scratch);
expect(actions).to.deep.equal(['mounted 1', 'mounted 2', 'mounted 3']);

render(<App y="2" />, scratch);
expect(actions).to.deep.equal(['mounted 1', 'mounted 2', 'mounted 3']);
});
});
29 changes: 29 additions & 0 deletions test/browser/render.test.js
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Original file line number Diff line number Diff line change
Expand Up @@ -1967,4 +1967,33 @@ describe('render()', () => {
'<head><title>Test</title></head><body><p>Test</p></body>\n'
);
});

it('should not remount components when replacing a component with a falsy value in-between', () => {
const actions = [];
class Comp extends Component {
componentDidMount() {
actions.push('mounted ' + this.props.i);
}
render() {
return <div>Hello</div>;
}
}

const App = props => {
return (
<div>
{props.y === '1' ? <Comp i={1} /> : <div />}
{false}
<Comp i={2} />
<Comp i={3} />
</div>
);
};

render(<App y="1" />, scratch);
expect(actions).to.deep.equal(['mounted 1', 'mounted 2', 'mounted 3']);

render(<App y="2" />, scratch);
expect(actions).to.deep.equal(['mounted 1', 'mounted 2', 'mounted 3']);
});
});
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