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diff.js
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diff.js
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import { ATTR_KEY } from '../constants';
import { isSameNodeType, isNamedNode } from './index';
import { buildComponentFromVNode } from './component';
import { createNode, setAccessor } from '../dom/index';
import { unmountComponent } from './component';
import options from '../options';
import { applyRef } from '../util';
import { removeNode } from '../dom/index';
/**
* Queue of components that have been mounted and are awaiting componentDidMount
* @type {Array<import('../component').Component>}
*/
export const mounts = [];
/** Diff recursion count, used to track the end of the diff cycle. */
export let diffLevel = 0;
/** Global flag indicating if the diff is currently within an SVG */
let isSvgMode = false;
/** Global flag indicating if the diff is performing hydration */
let hydrating = false;
/** Invoke queued componentDidMount lifecycle methods */
export function flushMounts() {
let c, i;
for (i=0; i<mounts.length; ++i) {
c = mounts[i];
if (options.afterMount) options.afterMount(c);
if (c.componentDidMount) c.componentDidMount();
}
mounts.length = 0;
}
/**
* Apply differences in a given vnode (and it's deep children) to a real DOM Node.
* @param {import('../dom').PreactElement} dom A DOM node to mutate into the shape of a `vnode`
* @param {import('../vnode').VNode} vnode A VNode (with descendants forming a tree) representing
* the desired DOM structure
* @param {object} context The current context
* @param {boolean} mountAll Whether or not to immediately mount all components
* @param {Element} parent ?
* @param {boolean} componentRoot ?
* @returns {import('../dom').PreactElement} The created/mutated element
* @private
*/
export function diff(dom, vnode, context, mountAll, parent, componentRoot) {
// diffLevel having been 0 here indicates initial entry into the diff (not a subdiff)
if (!diffLevel++) {
// when first starting the diff, check if we're diffing an SVG or within an SVG
isSvgMode = parent!=null && parent.ownerSVGElement!==undefined;
// hydration is indicated by the existing element to be diffed not having a prop cache
hydrating = dom!=null && !(ATTR_KEY in dom);
}
let ret = idiff(dom, vnode, context, mountAll, componentRoot);
// append the element if its a new parent
if (parent && ret.parentNode!==parent) parent.appendChild(ret);
// diffLevel being reduced to 0 means we're exiting the diff
if (!--diffLevel) {
hydrating = false;
// invoke queued componentDidMount lifecycle methods
if (!componentRoot) flushMounts();
}
return ret;
}
/**
* Internals of `diff()`, separated to allow bypassing diffLevel / mount flushing.
* @param {import('../dom').PreactElement} dom A DOM node to mutate into the shape of a `vnode`
* @param {import('../vnode').VNode} vnode A VNode (with descendants forming a tree) representing the desired DOM structure
* @param {object} context The current context
* @param {boolean} mountAll Whether or not to immediately mount all components
* @param {boolean} [componentRoot] ?
* @private
*/
function idiff(dom, vnode, context, mountAll, componentRoot) {
let out = dom,
prevSvgMode = isSvgMode;
// empty values (null, undefined, booleans) render as empty Text nodes
if (vnode==null || typeof vnode==='boolean') vnode = '';
// Fast case: Strings & Numbers create/update Text nodes.
if (typeof vnode==='string' || typeof vnode==='number') {
// update if it's already a Text node:
if (dom && dom.splitText!==undefined && dom.parentNode && (!dom._component || componentRoot)) {
/* istanbul ignore if */ /* Browser quirk that can't be covered: https://github.com/developit/preact/commit/fd4f21f5c45dfd75151bd27b4c217d8003aa5eb9 */
if (dom.nodeValue!=vnode) {
dom.nodeValue = vnode;
}
}
else {
// it wasn't a Text node: replace it with one and recycle the old Element
out = document.createTextNode(vnode);
if (dom) {
if (dom.parentNode) dom.parentNode.replaceChild(out, dom);
recollectNodeTree(dom, true);
}
}
out[ATTR_KEY] = true;
return out;
}
// If the VNode represents a Component, perform a component diff:
let vnodeName = vnode.nodeName;
if (typeof vnodeName==='function') {
return buildComponentFromVNode(dom, vnode, context, mountAll);
}
// Tracks entering and exiting SVG namespace when descending through the tree.
isSvgMode = vnodeName==='svg' ? true : vnodeName==='foreignObject' ? false : isSvgMode;
// If there's no existing element or it's the wrong type, create a new one:
vnodeName = String(vnodeName);
if (!dom || !isNamedNode(dom, vnodeName)) {
out = createNode(vnodeName, isSvgMode);
if (dom) {
// move children into the replacement node
while (dom.firstChild) out.appendChild(dom.firstChild);
// if the previous Element was mounted into the DOM, replace it inline
if (dom.parentNode) dom.parentNode.replaceChild(out, dom);
// recycle the old element (skips non-Element node types)
recollectNodeTree(dom, true);
}
}
let fc = out.firstChild,
props = out[ATTR_KEY],
vchildren = vnode.children;
if (props==null) {
props = out[ATTR_KEY] = {};
for (let a=out.attributes, i=a.length; i--; ) props[a[i].name] = a[i].value;
}
// Optimization: fast-path for elements containing a single TextNode:
if (!hydrating && vchildren && vchildren.length===1 && typeof vchildren[0]==='string' && fc!=null && fc.splitText!==undefined && fc.nextSibling==null) {
if (fc.nodeValue!=vchildren[0]) {
fc.nodeValue = vchildren[0];
}
}
// otherwise, if there are existing or new children, diff them:
else if (vchildren && vchildren.length || fc!=null) {
innerDiffNode(out, vchildren, context, mountAll, hydrating || props.dangerouslySetInnerHTML!=null);
}
// Apply attributes/props from VNode to the DOM Element:
diffAttributes(out, vnode.attributes, props);
// restore previous SVG mode: (in case we're exiting an SVG namespace)
isSvgMode = prevSvgMode;
return out;
}
/**
* Apply child and attribute changes between a VNode and a DOM Node to the DOM.
* @param {import('../dom').PreactElement} dom Element whose children should be compared & mutated
* @param {Array<import('../vnode').VNode>} vchildren Array of VNodes to compare to `dom.childNodes`
* @param {object} context Implicitly descendant context object (from most
* recent `getChildContext()`)
* @param {boolean} mountAll Whether or not to immediately mount all components
* @param {boolean} isHydrating if `true`, consumes externally created elements
* similar to hydration
*/
function innerDiffNode(dom, vchildren, context, mountAll, isHydrating) {
let originalChildren = dom.childNodes,
children = [],
keyed = {},
keyedLen = 0,
min = 0,
len = originalChildren.length,
childrenLen = 0,
vlen = vchildren ? vchildren.length : 0,
j, c, f, vchild, child;
// Build up a map of keyed children and an Array of unkeyed children:
if (len!==0) {
for (let i=0; i<len; i++) {
let child = originalChildren[i],
props = child[ATTR_KEY],
key = vlen && props ? child._component ? child._component.__key : props.key : null;
if (key!=null) {
keyedLen++;
keyed[key] = child;
}
else if (props || (child.splitText!==undefined ? (isHydrating ? child.nodeValue.trim() : true) : isHydrating)) {
children[childrenLen++] = child;
}
}
}
if (vlen!==0) {
for (let i=0; i<vlen; i++) {
vchild = vchildren[i];
child = null;
// attempt to find a node based on key matching
let key = vchild.key;
if (key!=null) {
if (keyedLen && keyed[key]!==undefined) {
child = keyed[key];
keyed[key] = undefined;
keyedLen--;
}
}
// attempt to pluck a node of the same type from the existing children
else if (min<childrenLen) {
for (j=min; j<childrenLen; j++) {
if (children[j]!==undefined && isSameNodeType(c = children[j], vchild, isHydrating)) {
child = c;
children[j] = undefined;
if (j===childrenLen-1) childrenLen--;
if (j===min) min++;
break;
}
}
}
// morph the matched/found/created DOM child to match vchild (deep)
child = idiff(child, vchild, context, mountAll);
f = originalChildren[i];
if (child && child!==dom && child!==f) {
if (f==null) {
dom.appendChild(child);
}
else if (child===f.nextSibling) {
removeNode(f);
}
else {
dom.insertBefore(child, f);
}
}
}
}
// remove unused keyed children:
if (keyedLen) {
for (let i in keyed) if (keyed[i]!==undefined) recollectNodeTree(keyed[i], false);
}
// remove orphaned unkeyed children:
while (min<=childrenLen) {
if ((child = children[childrenLen--])!==undefined) recollectNodeTree(child, false);
}
}
/**
* Recursively recycle (or just unmount) a node and its descendants.
* @param {import('../dom').PreactElement} node DOM node to start
* unmount/removal from
* @param {boolean} [unmountOnly=false] If `true`, only triggers unmount
* lifecycle, skips removal
*/
export function recollectNodeTree(node, unmountOnly) {
let component = node._component;
if (component) {
// if node is owned by a Component, unmount that component (ends up recursing back here)
unmountComponent(component);
}
else {
// If the node's VNode had a ref function, invoke it with null here.
// (this is part of the React spec, and smart for unsetting references)
if (node[ATTR_KEY]!=null) applyRef(node[ATTR_KEY].ref, null);
if (unmountOnly===false || node[ATTR_KEY]==null) {
removeNode(node);
}
removeChildren(node);
}
}
/**
* Recollect/unmount all children.
* - we use .lastChild here because it causes less reflow than .firstChild
* - it's also cheaper than accessing the .childNodes Live NodeList
*/
export function removeChildren(node) {
node = node.lastChild;
while (node) {
let next = node.previousSibling;
recollectNodeTree(node, true);
node = next;
}
}
/**
* Apply differences in attributes from a VNode to the given DOM Element.
* @param {import('../dom').PreactElement} dom Element with attributes to diff `attrs` against
* @param {object} attrs The desired end-state key-value attribute pairs
* @param {object} old Current/previous attributes (from previous VNode or
* element's prop cache)
*/
function diffAttributes(dom, attrs, old) {
let name;
// remove attributes no longer present on the vnode by setting them to undefined
for (name in old) {
if (!(attrs && attrs[name]!=null) && old[name]!=null) {
setAccessor(dom, name, old[name], old[name] = undefined, isSvgMode);
}
}
// add new & update changed attributes
for (name in attrs) {
if (name!=='children' && name!=='innerHTML' && (!(name in old) || attrs[name]!==(name==='value' || name==='checked' ? dom[name] : old[name]))) {
setAccessor(dom, name, old[name], old[name] = attrs[name], isSvgMode);
}
}
}