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children.js
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children.js
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import { diff, unmount, applyRef } from './index';
import { createVNode, Fragment } from '../create-element';
import { EMPTY_OBJ, EMPTY_ARR, INSERT_VNODE, MATCHED } from '../constants';
import { isArray } from '../util';
import { getDomSibling } from '../component';
/**
* Diff the children of a virtual node
* @param {PreactElement} parentDom The DOM element whose children are being
* diffed
* @param {ComponentChildren[]} renderResult
* @param {VNode} newParentVNode The new virtual node whose children should be
* diff'ed against oldParentVNode
* @param {VNode} oldParentVNode The old virtual node whose children should be
* diff'ed against newParentVNode
* @param {object} globalContext The current context object - modified by
* getChildContext
* @param {string} namespace Current namespace of the DOM node (HTML, SVG, or MathML)
* @param {Array<PreactElement>} excessDomChildren
* @param {Array<Component>} commitQueue List of components which have callbacks
* to invoke in commitRoot
* @param {PreactElement} oldDom The current attached DOM element any new dom
* elements should be placed around. Likely `null` on first render (except when
* hydrating). Can be a sibling DOM element when diffing Fragments that have
* siblings. In most cases, it starts out as `oldChildren[0]._dom`.
* @param {boolean} isHydrating Whether or not we are in hydration
* @param {any[]} refQueue an array of elements needed to invoke refs
*/
export function diffChildren(
parentDom,
renderResult,
newParentVNode,
oldParentVNode,
globalContext,
namespace,
excessDomChildren,
commitQueue,
oldDom,
isHydrating,
refQueue
) {
let i,
/** @type {VNode} */
oldVNode,
/** @type {VNode} */
childVNode,
/** @type {PreactElement} */
newDom,
/** @type {PreactElement} */
firstChildDom;
// This is a compression of oldParentVNode!=null && oldParentVNode != EMPTY_OBJ && oldParentVNode._children || EMPTY_ARR
// as EMPTY_OBJ._children should be `undefined`.
/** @type {VNode[]} */
let oldChildren = (oldParentVNode && oldParentVNode._children) || EMPTY_ARR;
let newChildrenLength = renderResult.length;
newParentVNode._nextDom = oldDom;
constructNewChildrenArray(newParentVNode, renderResult, oldChildren);
oldDom = newParentVNode._nextDom;
for (i = 0; i < newChildrenLength; i++) {
childVNode = newParentVNode._children[i];
if (childVNode == null) continue;
// At this point, constructNewChildrenArray has assigned _index to be the
// matchingIndex for this VNode's oldVNode (or -1 if there is no oldVNode).
if (childVNode._index === -1) {
oldVNode = EMPTY_OBJ;
} else {
oldVNode = oldChildren[childVNode._index] || EMPTY_OBJ;
}
// Update childVNode._index to its final index
childVNode._index = i;
// Morph the old element into the new one, but don't append it to the dom yet
diff(
parentDom,
childVNode,
oldVNode,
globalContext,
namespace,
excessDomChildren,
commitQueue,
oldDom,
isHydrating,
refQueue
);
// Adjust DOM nodes
newDom = childVNode._dom;
if (childVNode.ref && oldVNode.ref != childVNode.ref) {
if (oldVNode.ref) {
applyRef(oldVNode.ref, null, childVNode);
}
refQueue.push(
childVNode.ref,
childVNode._component || newDom,
childVNode
);
}
if (firstChildDom == null && newDom != null) {
firstChildDom = newDom;
}
if (
childVNode._flags & INSERT_VNODE ||
oldVNode._children === childVNode._children
) {
oldDom = insert(childVNode, oldDom, parentDom);
} else if (
typeof childVNode.type == 'function' &&
childVNode._nextDom !== undefined
) {
// Since Fragments or components that return Fragment like VNodes can
// contain multiple DOM nodes as the same level, continue the diff from
// the sibling of last DOM child of this child VNode
oldDom = childVNode._nextDom;
} else if (newDom) {
oldDom = newDom.nextSibling;
}
// Eagerly cleanup _nextDom. We don't need to persist the value because it
// is only used by `diffChildren` to determine where to resume the diff
// after diffing Components and Fragments. Once we store it the nextDOM
// local var, we can clean up the property. Also prevents us hanging on to
// DOM nodes that may have been unmounted.
childVNode._nextDom = undefined;
// Unset diffing flags
childVNode._flags &= ~(INSERT_VNODE | MATCHED);
}
// TODO: With new child diffing algo, consider alt ways to diff Fragments.
// Such as dropping oldDom and moving fragments in place
//
// Because the newParentVNode is Fragment-like, we need to set it's
// _nextDom property to the nextSibling of its last child DOM node.
//
// `oldDom` contains the correct value here because if the last child
// is a Fragment-like, then oldDom has already been set to that child's _nextDom.
// If the last child is a DOM VNode, then oldDom will be set to that DOM
// node's nextSibling.
newParentVNode._nextDom = oldDom;
newParentVNode._dom = firstChildDom;
}
/**
* @param {VNode} newParentVNode
* @param {ComponentChildren[]} renderResult
* @param {VNode[]} oldChildren
*/
function constructNewChildrenArray(newParentVNode, renderResult, oldChildren) {
/** @type {number} */
let i;
/** @type {VNode} */
let childVNode;
/** @type {VNode} */
let oldVNode;
const newChildrenLength = renderResult.length;
let oldChildrenLength = oldChildren.length,
remainingOldChildren = oldChildrenLength;
let skew = 0;
newParentVNode._children = [];
for (i = 0; i < newChildrenLength; i++) {
// @ts-expect-error We are reusing the childVNode variable to hold both the
// pre and post normalized childVNode
childVNode = renderResult[i];
if (
childVNode == null ||
typeof childVNode == 'boolean' ||
typeof childVNode == 'function'
) {
childVNode = newParentVNode._children[i] = null;
continue;
}
// If this newVNode is being reused (e.g. <div>{reuse}{reuse}</div>) in the same diff,
// or we are rendering a component (e.g. setState) copy the oldVNodes so it can have
// it's own DOM & etc. pointers
else if (
typeof childVNode == 'string' ||
typeof childVNode == 'number' ||
// eslint-disable-next-line valid-typeof
typeof childVNode == 'bigint' ||
childVNode.constructor == String
) {
childVNode = newParentVNode._children[i] = createVNode(
null,
childVNode,
null,
null,
null
);
} else if (isArray(childVNode)) {
childVNode = newParentVNode._children[i] = createVNode(
Fragment,
{ children: childVNode },
null,
null,
null
);
} else if (childVNode.constructor === undefined && childVNode._depth > 0) {
// VNode is already in use, clone it. This can happen in the following
// scenario:
// const reuse = <div />
// <div>{reuse}<span />{reuse}</div>
childVNode = newParentVNode._children[i] = createVNode(
childVNode.type,
childVNode.props,
childVNode.key,
childVNode.ref ? childVNode.ref : null,
childVNode._original
);
} else {
childVNode = newParentVNode._children[i] = childVNode;
}
const skewedIndex = i + skew;
childVNode._parent = newParentVNode;
childVNode._depth = newParentVNode._depth + 1;
// Temporarily store the matchingIndex on the _index property so we can pull
// out the oldVNode in diffChildren. We'll override this to the VNode's
// final index after using this property to get the oldVNode
const matchingIndex = (childVNode._index = findMatchingIndex(
childVNode,
oldChildren,
skewedIndex,
remainingOldChildren
));
oldVNode = null;
if (matchingIndex !== -1) {
oldVNode = oldChildren[matchingIndex];
remainingOldChildren--;
if (oldVNode) {
oldVNode._flags |= MATCHED;
}
}
// Here, we define isMounting for the purposes of the skew diffing
// algorithm. Nodes that are unsuspending are considered mounting and we detect
// this by checking if oldVNode._original === null
const isMounting = oldVNode == null || oldVNode._original === null;
if (isMounting) {
if (matchingIndex == -1) {
skew--;
}
// If we are mounting a DOM VNode, mark it for insertion
if (typeof childVNode.type != 'function') {
childVNode._flags |= INSERT_VNODE;
}
} else if (matchingIndex !== skewedIndex) {
// When we move elements around i.e. [0, 1, 2] --> [1, 0, 2]
// --> we diff 1, we find it at position 1 while our skewed index is 0 and our skew is 0
// we set the skew to 1 as we found an offset.
// --> we diff 0, we find it at position 0 while our skewed index is at 2 and our skew is 1
// this makes us increase the skew again.
// --> we diff 2, we find it at position 2 while our skewed index is at 4 and our skew is 2
//
// this becomes an optimization question where currently we see a 1 element offset as an insertion
// or deletion i.e. we optimize for [0, 1, 2] --> [9, 0, 1, 2]
// while a more than 1 offset we see as a swap.
// We could probably build heuristics for having an optimized course of action here as well, but
// might go at the cost of some bytes.
//
// If we wanted to optimize for i.e. only swaps we'd just do the last two code-branches and have
// only the first item be a re-scouting and all the others fall in their skewed counter-part.
// We could also further optimize for swaps
if (matchingIndex == skewedIndex - 1) {
skew--;
} else if (matchingIndex == skewedIndex + 1) {
skew++;
} else {
if (matchingIndex > skewedIndex) {
skew--;
} else {
skew++;
}
// Move this VNode's DOM if the original index (matchingIndex) doesn't
// match the new skew index (i + new skew)
// In the former two branches we know that it matches after skewing
childVNode._flags |= INSERT_VNODE;
}
}
}
// Remove remaining oldChildren if there are any. Loop forwards so that as we
// unmount DOM from the beginning of the oldChildren, we can adjust oldDom to
// point to the next child, which needs to be the first DOM node that won't be
// unmounted.
if (remainingOldChildren) {
for (i = 0; i < oldChildrenLength; i++) {
oldVNode = oldChildren[i];
if (oldVNode != null && (oldVNode._flags & MATCHED) === 0) {
if (oldVNode._dom == newParentVNode._nextDom) {
newParentVNode._nextDom = getDomSibling(oldVNode);
}
unmount(oldVNode, oldVNode);
}
}
}
}
/**
* @param {VNode} parentVNode
* @param {PreactElement} oldDom
* @param {PreactElement} parentDom
* @returns {PreactElement}
*/
function insert(parentVNode, oldDom, parentDom) {
// Note: VNodes in nested suspended trees may be missing _children.
if (typeof parentVNode.type == 'function') {
let children = parentVNode._children;
for (let i = 0; children && i < children.length; i++) {
if (children[i]) {
// If we enter this code path on sCU bailout, where we copy
// oldVNode._children to newVNode._children, we need to update the old
// children's _parent pointer to point to the newVNode (parentVNode
// here).
children[i]._parent = parentVNode;
oldDom = insert(children[i], oldDom, parentDom);
}
}
return oldDom;
} else if (parentVNode._dom != oldDom) {
if (oldDom && parentVNode.type && !parentDom.contains(oldDom)) {
oldDom = getDomSibling(parentVNode);
}
parentDom.insertBefore(parentVNode._dom, oldDom || null);
oldDom = parentVNode._dom;
}
do {
oldDom = oldDom && oldDom.nextSibling;
} while (oldDom != null && oldDom.nodeType === 8);
return oldDom;
}
/**
* Flatten and loop through the children of a virtual node
* @param {ComponentChildren} children The unflattened children of a virtual
* node
* @returns {VNode[]}
*/
export function toChildArray(children, out) {
out = out || [];
if (children == null || typeof children == 'boolean') {
} else if (isArray(children)) {
children.some(child => {
toChildArray(child, out);
});
} else {
out.push(children);
}
return out;
}
/**
* @param {VNode} childVNode
* @param {VNode[]} oldChildren
* @param {number} skewedIndex
* @param {number} remainingOldChildren
* @returns {number}
*/
function findMatchingIndex(
childVNode,
oldChildren,
skewedIndex,
remainingOldChildren
) {
const key = childVNode.key;
const type = childVNode.type;
let x = skewedIndex - 1;
let y = skewedIndex + 1;
let oldVNode = oldChildren[skewedIndex];
// We only need to perform a search if there are more children
// (remainingOldChildren) to search. However, if the oldVNode we just looked
// at skewedIndex was not already used in this diff, then there must be at
// least 1 other (so greater than 1) remainingOldChildren to attempt to match
// against. So the following condition checks that ensuring
// remainingOldChildren > 1 if the oldVNode is not already used/matched. Else
// if the oldVNode was null or matched, then there could needs to be at least
// 1 (aka `remainingOldChildren > 0`) children to find and compare against.
let shouldSearch =
remainingOldChildren >
(oldVNode != null && (oldVNode._flags & MATCHED) === 0 ? 1 : 0);
if (
oldVNode === null ||
(oldVNode &&
key == oldVNode.key &&
type === oldVNode.type &&
(oldVNode._flags & MATCHED) === 0)
) {
return skewedIndex;
} else if (shouldSearch) {
while (x >= 0 || y < oldChildren.length) {
if (x >= 0) {
oldVNode = oldChildren[x];
if (
oldVNode &&
(oldVNode._flags & MATCHED) === 0 &&
key == oldVNode.key &&
type === oldVNode.type
) {
return x;
}
x--;
}
if (y < oldChildren.length) {
oldVNode = oldChildren[y];
if (
oldVNode &&
(oldVNode._flags & MATCHED) === 0 &&
key == oldVNode.key &&
type === oldVNode.type
) {
return y;
}
y++;
}
}
}
return -1;
}