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Hoist _children into a local in constructNewChildrenArray #5198

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Merged
JoviDeCroock merged 2 commits into from
Aug 7, 2026
+11 −8
Merged

Hoist _children into a local in constructNewChildrenArray #5198

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Hoist _children into a local in constructNewChildrenArray
JoviDeCroock Aug 7, 2026
c0c3646
Merge branch 'main' into JoviDeCroock/issue-2618-algo-learnings
JoviDeCroock Aug 7, 2026
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19 changes: 11 additions & 8 deletions src/diff/children.js
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Original file line number Diff line number Diff line change
Expand Up @@ -182,7 +182,10 @@ function constructNewChildrenArray(
* real reorder happened and we need to compute the minimal set of moves. */
let moved = false;

newParentVNode._children = new Array(newChildrenLength);
// Hoisted: every normalization branch below writes through this array, so
// reading `_children` off the vnode each time is a wasted property load.
/** @type {VNode[]} */
let newChildren = (newParentVNode._children = new Array(newChildrenLength));
for (i = 0; i < newChildrenLength; i++) {
// @ts-expect-error We are reusing the childVNode variable to hold both the
// pre and post normalized childVNode
Expand All @@ -193,7 +196,7 @@ function constructNewChildrenArray(
typeof childVNode == 'boolean' ||
typeof childVNode == 'function'
) {
newParentVNode._children[i] = NULL;
newChildren[i] = NULL;
continue;
}
// If this newVNode is being reused (e.g. <div>{reuse}{reuse}</div>) in the same diff,
Expand All @@ -206,15 +209,15 @@ function constructNewChildrenArray(
typeof childVNode != 'object' ||
childVNode.constructor == String
) {
childVNode = newParentVNode._children[i] = createVNode(
childVNode = newChildren[i] = createVNode(
NULL,
childVNode,
NULL,
NULL,
NULL
);
} else if (isArray(childVNode)) {
childVNode = newParentVNode._children[i] = createVNode(
childVNode = newChildren[i] = createVNode(
Fragment,
{ children: childVNode },
NULL,
Expand All @@ -226,15 +229,15 @@ function constructNewChildrenArray(
// scenario:
// const reuse = <div />
// <div>{reuse}<span />{reuse}</div>
childVNode = newParentVNode._children[i] = createVNode(
childVNode = newChildren[i] = createVNode(
childVNode.type,
childVNode.props,
childVNode.key,
childVNode.ref || NULL,
childVNode._original
);
} else {
newParentVNode._children[i] = childVNode;
newChildren[i] = childVNode;
}

const skewedIndex = i + skew;
Expand Down Expand Up @@ -329,7 +332,7 @@ function constructNewChildrenArray(
/** @type {number[]} length of the longest increasing subsequence ending at child i */
let lisLengths = [];
for (i = 0; i < newChildrenLength; i++) {
childVNode = newParentVNode._children[i];
childVNode = newChildren[i];
if (childVNode && childVNode._flags & MATCHED) {
// Binary search for the insertion point, keeping the pass at
// O(n log n) even for pathological reorders.
Expand Down Expand Up @@ -357,7 +360,7 @@ function constructNewChildrenArray(
if (lisLengths[i] == skew) {
skew--;
} else {
newParentVNode._children[i]._flags |= INSERT_VNODE;
newChildren[i]._flags |= INSERT_VNODE;
}
}
}
Expand Down
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