preact/src/diff/index.js at main · preactjs/preact

736 lines (651 loc) · 20.2 KB
import { BaseComponent, getDomSibling } from '../component';
	COMPONENT_DIRTY,
	COMPONENT_FORCE,
	COMPONENT_PENDING_ERROR,
	COMPONENT_PROCESSING_EXCEPTION,
	EMPTY_ARR,
	EMPTY_OBJ,
	FORCE_PROPS_REVALIDATE,
	MATHML_TOKEN_ELEMENTS,
	MATH_NAMESPACE,
	MODE_HYDRATE,
	MODE_SUSPENDED,
	RESET_MODE,
	SVG_NAMESPACE,
	UNDEFINED,
	XHTML_NAMESPACE
} from '../constants';
import { Fragment } from '../create-element';
import options from '../options';
import { assign, isArray, removeNode, slice } from '../util';
import { diffChildren } from './children';
import { setProperty } from './props';
 * @typedef {import('../internal').ComponentType} ComponentType
 * @typedef {import('../internal').ComponentChildren} ComponentChildren
 * @typedef {import('../internal').Component} Component
 * @typedef {import('../internal').PreactElement} PreactElement
 * @typedef {import('../internal').VNode} VNode
 * @template {any} T
 * @typedef {import('../internal').Ref<T>} Ref<T>
 * Diff two virtual nodes and apply proper changes to the DOM
 * @param {PreactElement} parentDom The parent of the DOM element
 * @param {VNode} newVNode The new virtual node
 * @param {VNode} oldVNode The old virtual node
 * @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
 * @param {Document} doc The document object to use for creating elements
export function diff(
	parentDom,
	globalContext,
	namespace,
	excessDomChildren,
	commitQueue,
	isHydrating,
	/** @type {any} */
		newType = newVNode.type;
	// When passing through createElement it assigns the object
	// constructor as undefined. This to prevent JSON-injection.
	if (newVNode.constructor !== UNDEFINED) return NULL;
	// If the previous diff bailed out, resume creating/hydrating.
		oldVNode._flags & MODE_SUSPENDED &&
		// @ts-expect-error This is 1 or 0 (true or false)
		(isHydrating = oldVNode._flags & MODE_HYDRATE) &&
		oldVNode._component._excess
		excessDomChildren = oldVNode._component._excess;
		oldDom = excessDomChildren[0];
		oldVNode._component._excess = NULL;
	if ((tmp = options._diff)) tmp(newVNode);
	outer: if (typeof newType == 'function') {
				oldProps,
				oldState,
				snapshot,
				newProps = newVNode.props;
			const isClassComponent = newType.prototype && newType.prototype.render;
			// Necessary for createContext api. Setting this property will pass
			// the context value as `this.context` just for this component.
			tmp = newType.contextType;
			const provider = tmp && globalContext[tmp._id];
			const componentContext = tmp
				? provider
					? provider.props.value
					: tmp._defaultValue
				: globalContext;
			// Get component and set it to `c`
			if (oldVNode._component) {
				c = newVNode._component = oldVNode._component;
				if (c._bits & COMPONENT_PENDING_ERROR) {
					c._bits |= COMPONENT_PROCESSING_EXCEPTION;
			} else {
				// Instantiate the new component
				if (isClassComponent) {
					// @ts-expect-error Trust me, Component implements the interface we want
					newVNode._component = c = new newType(newProps, componentContext); // eslint-disable-line new-cap
				} else {
					// @ts-expect-error Trust me, Component implements the interface we want
					newVNode._component = c = new BaseComponent(
						newProps,
						componentContext
					c.constructor = newType;
					c.render = doRender;
				if (provider) provider.sub(c);
				if (!c.state) c.state = {};
				c._globalContext = globalContext;
				c._bits |= COMPONENT_DIRTY;
				c._renderCallbacks = [];
				c._stateCallbacks = [];
			// Invoke getDerivedStateFromProps
			if (isClassComponent && c._nextState == NULL) {
				c._nextState = c.state;
			if (isClassComponent && newType.getDerivedStateFromProps != NULL) {
				if (c._nextState == c.state) {
					c._nextState = assign({}, c._nextState);
				assign(
					c._nextState,
					newType.getDerivedStateFromProps(newProps, c._nextState)
			oldProps = c.props;
			oldState = c.state;
			c._vnode = newVNode;
			// Invoke pre-render lifecycle methods
			if (!oldVNode._component) {
					isClassComponent &&
					newType.getDerivedStateFromProps == NULL &&
					c.componentWillMount != NULL
					c.componentWillMount();
				if (isClassComponent && c.componentDidMount != NULL) {
					c._renderCallbacks.push(c.componentDidMount);
			} else {
					isClassComponent &&
					newType.getDerivedStateFromProps == NULL &&
					newProps !== oldProps &&
					c.componentWillReceiveProps != NULL
					c.componentWillReceiveProps(newProps, componentContext);
					newVNode._original == oldVNode._original ||
					(!(c._bits & COMPONENT_FORCE) &&
						c.shouldComponentUpdate != NULL &&
						c.shouldComponentUpdate(
							newProps,
							c._nextState,
							componentContext
						) === false)
					// More info about this here: https://gist.github.com/JoviDeCroock/bec5f2ce93544d2e6070ef8e0036e4e8
					if (newVNode._original != oldVNode._original) {
						// When we are dealing with a bail because of sCU we have to update
						// the props, state and dirty-state.
						// when we are dealing with strict-equality we don't as the child could still
						// be dirtied see #3883
						c.props = newProps;
						c.state = c._nextState;
						c._bits &= ~COMPONENT_DIRTY;
					newVNode._dom = oldVNode._dom;
					newVNode._children = oldVNode._children;
					newVNode._children.some(vnode => {
						if (vnode) vnode._parent = newVNode;
					EMPTY_ARR.push.apply(c._renderCallbacks, c._stateCallbacks);
					c._stateCallbacks = [];
					if (c._renderCallbacks.length) {
						commitQueue.push(c);
					break outer;
				if (c.componentWillUpdate != NULL) {
					c.componentWillUpdate(newProps, c._nextState, componentContext);
				if (isClassComponent && c.componentDidUpdate != NULL) {
					c._renderCallbacks.push(() => {
						c.componentDidUpdate(oldProps, oldState, snapshot);
			c.context = componentContext;
			c.props = newProps;
			c._parentDom = parentDom;
			c._bits &= ~COMPONENT_FORCE;
			let renderHook = options._render,
				count = 0;
			if (isClassComponent) {
				c.state = c._nextState;
				c._bits &= ~COMPONENT_DIRTY;
				if (renderHook) renderHook(newVNode);
				tmp = c.render(c.props, c.state, c.context);
				EMPTY_ARR.push.apply(c._renderCallbacks, c._stateCallbacks);
				c._stateCallbacks = [];
			} else {
					c._bits &= ~COMPONENT_DIRTY;
					if (renderHook) renderHook(newVNode);
					tmp = c.render(c.props, c.state, c.context);
					// Handle setState called in render, see #2553
					c.state = c._nextState;
				} while (c._bits & COMPONENT_DIRTY && ++count < 25);
			// Handle setState called in render, see #2553
			c.state = c._nextState;
			if (c.getChildContext != NULL) {
				globalContext = assign({}, globalContext, c.getChildContext());
				isClassComponent &&
				oldVNode._component &&
				c.getSnapshotBeforeUpdate != NULL
				snapshot = c.getSnapshotBeforeUpdate(oldProps, oldState);
			const renderResult =
				tmp != NULL && tmp.type === Fragment && tmp.key == NULL
					? cloneNode(tmp.props.children)
					: tmp;
			oldDom = diffChildren(
				parentDom,
				isArray(renderResult) ? renderResult : [renderResult],
				newVNode,
				oldVNode,
				globalContext,
				namespace,
				excessDomChildren,
				commitQueue,
				oldDom,
				isHydrating,
				refQueue,
			// We successfully rendered this VNode, unset any stored hydration/bailout state:
			newVNode._flags &= RESET_MODE;
			if (c._renderCallbacks.length) {
				commitQueue.push(c);
			if (c._bits & COMPONENT_PENDING_ERROR) {
				c._bits &= ~(COMPONENT_PROCESSING_EXCEPTION | COMPONENT_PENDING_ERROR);
		} catch (e) {
			newVNode._original = NULL;
			// if hydrating or creating initial tree, bailout preserves DOM:
			if (isHydrating || excessDomChildren != NULL) {
				if (e.then) {
					let commentMarkersToFind = 0,
						done;
					newVNode._flags |= isHydrating
						? MODE_HYDRATE | MODE_SUSPENDED
						: MODE_SUSPENDED;
					newVNode._component._excess = [];
					for (let i = 0; i < excessDomChildren.length; i++) {
						const child = excessDomChildren[i];
						if (child == NULL || done) continue;
						// When we encounter a boundary with $s we are opening
						// a boundary, this implies that we need to bump
						// the amount of markers we need to find before closing
						// the outer boundary.
						// We exclude the open and closing marker from
						// the future excessDomChildren but any nested one
						// needs to be included for future suspensions.
						if (child.nodeType == 8) {
							if (child.data == '$s') {
								if (commentMarkersToFind) {
									newVNode._component._excess.push(child);
								commentMarkersToFind++;
							} else if (child.data == '/$s') {
								commentMarkersToFind--;
								if (commentMarkersToFind) {
									newVNode._component._excess.push(child);
								done = commentMarkersToFind == 0;
								oldDom = excessDomChildren[i];
							excessDomChildren[i] = NULL;
						} else if (commentMarkersToFind) {
							newVNode._component._excess.push(child);
							excessDomChildren[i] = NULL;
					if (!done) {
						while (oldDom && oldDom.nodeType == 8 && oldDom.nextSibling) {
							oldDom = oldDom.nextSibling;
						excessDomChildren[excessDomChildren.indexOf(oldDom)] = NULL;
						newVNode._component._excess = [oldDom];
					newVNode._dom = oldDom;
				} else {
					for (let i = excessDomChildren.length; i--; ) {
						removeNode(excessDomChildren[i]);
					markAsForce(newVNode);
			} else {
				newVNode._dom = oldVNode._dom;
				newVNode._children = oldVNode._children;
				if (!e.then) markAsForce(newVNode);
			options._catchError(e, newVNode, oldVNode);
		oldDom = newVNode._dom = diffElementNodes(
			oldVNode._dom,
			newVNode,
			oldVNode,
			globalContext,
			namespace,
			excessDomChildren,
			commitQueue,
			isHydrating,
			refQueue,
	if ((tmp = options.diffed)) tmp(newVNode);
	return newVNode._flags & MODE_SUSPENDED ? UNDEFINED : oldDom;
function markAsForce(vnode) {
	if (vnode && vnode._component) vnode._component._bits |= COMPONENT_FORCE;
	if (vnode && vnode._children) vnode._children.forEach(markAsForce);
 * @param {Array<Component>} commitQueue List of components
 * which have callbacks to invoke in commitRoot
 * @param {VNode} root
export function commitRoot(commitQueue, root, refQueue) {
	for (let i = 0; i < refQueue.length; i++) {
		applyRef(refQueue[i], refQueue[++i], refQueue[++i]);
	if (options._commit) options._commit(root, commitQueue);
	commitQueue.some(c => {
			// @ts-expect-error Reuse the commitQueue variable here so the type changes
			commitQueue = c._renderCallbacks;
			c._renderCallbacks = [];
			commitQueue.some(cb => {
				// @ts-expect-error See above comment on commitQueue
				cb.call(c);
		} catch (e) {
			options._catchError(e, c._vnode);
function cloneNode(node) {
	if (typeof node != 'object' || node == NULL || node._depth > 0) {
		return node;
	if (isArray(node)) {
		return node.map(cloneNode);
	if (node.constructor !== UNDEFINED) return null;
	return assign({}, node);
 * Diff two virtual nodes representing DOM element
 * @param {PreactElement} dom The DOM element representing the virtual nodes
 * being diffed
 * @param {VNode} newVNode The new virtual node
 * @param {VNode} oldVNode The old virtual node
 * @param {object} globalContext The current context object
 * @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 {boolean} isHydrating Whether or not we are in hydration
 * @param {any[]} refQueue an array of elements needed to invoke refs
 * @param {Document} doc The document object to use for creating elements
 * @returns {PreactElement}
function diffElementNodes(
	globalContext,
	namespace,
	excessDomChildren,
	commitQueue,
	isHydrating,
	let oldProps = oldVNode.props || EMPTY_OBJ;
	const newProps = newVNode.props;
	const nodeType = /** @type {string} */ (newVNode.type);
	/** @type {any} */
	/** @type {{ __html?: string }} */
	let newHtml;
	/** @type {{ __html?: string }} */
	let oldHtml;
	/** @type {ComponentChildren} */
	let newChildren;
	let value;
	let inputValue;
	let checked;
	// Tracks entering and exiting namespaces when descending through the tree.
	if (nodeType == 'svg') namespace = SVG_NAMESPACE;
	else if (nodeType == 'math') namespace = MATH_NAMESPACE;
	else if (!namespace) namespace = XHTML_NAMESPACE;
	if (excessDomChildren != NULL) {
		for (i = 0; i < excessDomChildren.length; i++) {
			value = excessDomChildren[i];
			// if newVNode matches an element in excessDomChildren or the `dom`
			// argument matches an element in excessDomChildren, remove it from
			// excessDomChildren so it isn't later removed in diffChildren
				value &&
				'setAttribute' in value == !!nodeType &&
				(nodeType ? value.localName == nodeType : value.nodeType == 3)
				dom = value;
				excessDomChildren[i] = NULL;
	if (dom == NULL) {
		if (nodeType == NULL) {
			return doc.createTextNode(newProps);
		dom = doc.createElementNS(namespace, nodeType, newProps.is && newProps);
		// we are creating a new node, so we can assume this is a new subtree (in
		// case we are hydrating), this deopts the hydrate
		if (isHydrating) {
			if (options._hydrationMismatch)
				options._hydrationMismatch(newVNode, excessDomChildren);
			isHydrating = false;
		// we created a new parent, so none of the previously attached children can be reused:
		excessDomChildren = NULL;
	if (nodeType == NULL) {
		// During hydration, we still have to split merged text from SSR'd HTML.
		if (oldProps !== newProps && (!isHydrating || dom.data != newProps)) {
			dom.data = newProps;
		// If excessDomChildren was not null, repopulate it with the current element's children:
		excessDomChildren =
			nodeType == 'textarea' && newProps.defaultValue != NULL
				: excessDomChildren && slice.call(dom.childNodes);
		// If we are in a situation where we are not hydrating but are using
		// existing DOM (e.g. replaceNode) we should read the existing DOM
		// attributes to diff them
		if (!isHydrating && excessDomChildren != NULL) {
			oldProps = {};
			for (i = 0; i < dom.attributes.length; i++) {
				value = dom.attributes[i];
				oldProps[value.name] = value.value;
		for (i in oldProps) {
			value = oldProps[i];
			if (i == 'dangerouslySetInnerHTML') {
				oldHtml = value;
			} else if (
				i != 'children' &&
				!(i in newProps) &&
				!(i == 'value' && 'defaultValue' in newProps) &&
				!(i == 'checked' && 'defaultChecked' in newProps)
				setProperty(dom, i, NULL, value, namespace);
		// During hydration, props are not diffed at all (including dangerouslySetInnerHTML)
		// @TODO we should warn in debug mode when props don't match here.
		const shouldRevalidateProps = oldVNode._flags & FORCE_PROPS_REVALIDATE;
		for (i in newProps) {
			value = newProps[i];
			if (i == 'children') {
				newChildren = value;
			} else if (i == 'dangerouslySetInnerHTML') {
				newHtml = value;
			} else if (i == 'value') {
				inputValue = value;
			} else if (i == 'checked') {
				checked = value;
			} else if (
				(!isHydrating || typeof value == 'function') &&
				(oldProps[i] !== value || shouldRevalidateProps)
				setProperty(dom, i, value, oldProps[i], namespace);
		// If the new vnode didn't have dangerouslySetInnerHTML, diff its children
		if (newHtml) {
			// Avoid re-applying the same '__html' if it did not changed between re-render
				!isHydrating &&
				(!oldHtml ||
					(newHtml.__html != oldHtml.__html && newHtml.__html != dom.innerHTML))
				dom.innerHTML = newHtml.__html;
			newVNode._children = [];
			if (oldHtml) dom.innerHTML = '';
				nodeType == 'foreignObject' ||
				(namespace == MATH_NAMESPACE && MATHML_TOKEN_ELEMENTS.test(nodeType))
				namespace = XHTML_NAMESPACE;
			diffChildren(
				// @ts-expect-error
				nodeType == 'template' ? dom.content : dom,
				isArray(newChildren) ? newChildren : [newChildren],
				newVNode,
				oldVNode,
				globalContext,
				namespace,
				excessDomChildren,
				commitQueue,
				excessDomChildren
					? excessDomChildren[0]
					: oldVNode._children && getDomSibling(oldVNode, 0),
				isHydrating,
				refQueue,
			// Remove children that are not part of any vnode.
			if (excessDomChildren != NULL) {
				for (i = excessDomChildren.length; i--; ) {
					removeNode(excessDomChildren[i]);
		// As above, don't diff props during hydration
		if (!isHydrating || nodeType == 'textarea') {
			i = 'value';
			if (nodeType == 'progress' && inputValue == NULL) {
				dom.removeAttribute('value');
			} else if (
				inputValue != UNDEFINED &&
				// #2756 For the <progress>-element the initial value is 0,
				// despite the attribute not being present. When the attribute
				// is missing the progress bar is treated as indeterminate.
				// To fix that we'll always update it when it is 0 for progress elements
				(inputValue !== dom[i] || (nodeType === 'progress' && !inputValue))
				setProperty(dom, i, inputValue, oldProps[i], namespace);
			i = 'checked';
			if (checked != UNDEFINED && checked != dom[i]) {
				setProperty(dom, i, checked, oldProps[i], namespace);
	return dom;
 * Invoke or update a ref, depending on whether it is a function or object ref.
 * @param {Ref<any> & { _unmount?: unknown }} ref
 * @param {any} value
 * @param {VNode} vnode
export function applyRef(ref, value, vnode) {
		if (typeof ref == 'function') {
			if (typeof ref._unmount == 'function') {
				ref._unmount();
			if (typeof ref._unmount != 'function' || value != NULL) {
				// Store the cleanup function on the function
				// instance object itself to avoid shape
				// transitioning vnode
				ref._unmount = ref(value);
		} else ref.current = value;
	} catch (e) {
		options._catchError(e, vnode);
 * Unmount a virtual node from the tree and apply DOM changes
 * @param {VNode} vnode The virtual node to unmount
 * @param {VNode} parentVNode The parent of the VNode that initiated the unmount
 * @param {boolean} [skipRemove] Flag that indicates that a parent node of the
 * current element is already detached from the DOM.
export function unmount(vnode, parentVNode, skipRemove) {
	if (options.unmount) options.unmount(vnode);
	if ((r = vnode.ref) && (!r.current || r.current == vnode._dom)) {
		applyRef(r, NULL, parentVNode);
	if ((r = vnode._component) != NULL) {
		if (r.componentWillUnmount) {
				r.componentWillUnmount();
			} catch (e) {
				options._catchError(e, parentVNode);
		r._parentDom = NULL;
	if ((r = vnode._children)) {
		for (let i = 0; i < r.length; i++) {
			if (r[i]) {
				unmount(
					parentVNode,
					skipRemove || typeof vnode.type != 'function'
	if (!skipRemove) {
		removeNode(vnode._dom);
	if (vnode._dom && vnode._dom._listeners) {
		vnode._dom._listeners = NULL;
	vnode._dom = vnode._component = vnode._parent = NULL;
/** The `.render()` method for a PFC backing instance. */
function doRender(props, state, context) {
	return this.constructor(props, context);
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