react15-源码演化-组件更新setState（三）
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2022-07-02 23:46:49
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组件更新
- 组件更新判断逻辑如下图:
1. 合并state
1.1. src/index.js
import React from './react';
import ReactDOM from './react-dom';
class Counter extends React.Component {
constructor(props) {
super(props);
this.state = { number: 0 };
setTimeout(() => {
this.setState({ number: this.state.number + 1 });
console.log(this.state);
}, 1000);
}
render() {
return <div id={'counter' + this.state.number}>+</div>
}
}
ReactDOM.render(
<Counter />,
document.getElementById('root')
);
1.2. src/react/component.js
//更新队列
export const updateQueue = {
updaters: [],//要执行的updater对象
isPending: false,//是否处于批量更新模式
};
class Updater {
constructor(componentInstance) {
this.componentInstance = componentInstance;//Updater和类组件1对1关系
this.pendingStates = [];//更新如果批量的，先把状态暂存到数组，最后更新时统一合并
this.nextProps = null;//新的属性对象
}
addState(partialState){
this.pendingStates.push(partialState);//把新状态放入数组
this.emitUpdate();
}
emitUpdate(nextProps){
this.nextProps = nextProps;
//如果有新属性对象 或者 队列处于‘休息’状态，直接更新
if (nextProps || !updateQueue.isPending) {
this.updateComponent();
} else {//否则交给队列处理
updateQueue.add(this);
}
}
updateComponent(){
let { componentInstance, pendingStates, nextProps } = this;
if (nextProps || pendingStates.length > 0) {//长度大于0，有要合并的状态
shouldUpdate(componentInstance, nextProps, this.getState());
}
}
//合并及返回新的状态
getState(){
let { componentInstance, pendingStates } = this;
let { state } = componentInstance;//老组件当前状态
if (pendingStates.length > 0) {
//迭代pendingStates，将所有状态合并到state
for (let i = 0; i < pendingStates.length; i++) {
let nextState = pendingStates[i];
if (typeof nextState === 'function') {
state = { ...state, ...nextState.call(componentInstance, state) };
} else {
state = { ...state, ...nextState };
}
}
}
pendingStates.length = 0;//合并后清空数组
return state;
}
}
//判断是否要更新
function shouldUpdate(componentInstance, nextProps, nextState) {
componentInstance.props = nextProps;//将新props赋给组件
componentInstance.state = nextState;//将新state赋给组件
if (
componentInstance.shouldComponentUpdate &&
!componentInstance.shouldComponentUpdate(nextProps, nextState)
) {
//如果shouldComponentUpdate返回false，则不更新
return false;
}
componentInstance.forceUpdate();//让组件强制更新
}
class Component {
constructor(props) {
this.props = props;
this.$updater = new Updater(this); //this 就是类组件的实例
this.state = {}; // 当前状态
this.nextProps = null; // 下一个属性对象
}
//批量更新 partial，状态可能会被合并
setState(partialState) {
this.$updater.addState(partialState);
}
forceUpdate(){//进行组件更新
}
}
//类组件的本质也是函数(请参考new Class原理)，通过`isReactComponent`判断是类组件还是函数组件
Component.prototype.isReactComponent = {};
export {
Component
}
2. 简单替换DOM
2.1. src/react/component.js
import { compareTwoElements } from './vdom';
//更新队列
export const updateQueue = {
updaters: [],//要执行的updater对象
isPending: false,//是否处于批量更新模式
};
class Updater {
constructor(componentInstance) {
this.componentInstance = componentInstance;//Updater和类组件1对1关系
this.pendingStates = [];//更新如果批量的，先把状态暂存到数组，最后更新时统一合并
this.nextProps = null;//新的属性对象
}
addState(partialState){
this.pendingStates.push(partialState);//把新状态放入数组
this.emitUpdate();
}
emitUpdate(nextProps){
this.nextProps = nextProps;
//如果有新属性对象 或者 队列处于‘休息’状态，直接更新
if (nextProps || !updateQueue.isPending) {
this.updateComponent();
} else {//否则交给队列处理
updateQueue.add(this);
}
}
updateComponent(){
let { componentInstance, pendingStates, nextProps } = this;
if (nextProps || pendingStates.length > 0) {//长度大于0，有要合并的状态
shouldUpdate(componentInstance, nextProps, this.getState());
}
}
//合并及返回新的状态
getState(){
let { componentInstance, pendingStates } = this;
let { state } = componentInstance;//老组件当前状态
if (pendingStates.length > 0) {
//迭代pendingStates，将所有状态合并到state
for (let i = 0; i < pendingStates.length; i++) {
let nextState = pendingStates[i];
if (typeof nextState === 'function') {
state = { ...state, ...nextState.call(componentInstance, state) };
} else {
state = { ...state, ...nextState };
}
}
}
pendingStates.length = 0;//合并后清空数组
return state;
}
}
//判断是否要更新
function shouldUpdate(componentInstance, nextProps, nextState) {
componentInstance.props = nextProps;//将新props赋给组件
componentInstance.state = nextState;//将新state赋给组件
if (
componentInstance.shouldComponentUpdate &&
!componentInstance.shouldComponentUpdate(nextProps, nextState)
) {
//如果shouldComponentUpdate返回false，则不更新
return false;
}
componentInstance.forceUpdate();//让组件强制更新
}
class Component {
constructor(props) {
this.props = props;
this.$updater = new Updater(this); //this 就是类组件的实例
this.state = {}; // 当前状态
this.nextProps = null; // 下一个属性对象
}
//批量更新 partial，状态可能会被合并
setState(partialState) {
this.$updater.addState(partialState);
}
forceUpdate(){//进行组件更新
let { props, state, renderElement: oldRenderElement } = this;
if (this.componentWillUpdate) {
this.componentWillUpdate();
}
let newRenderElement = this.render();
let currentElement = compareTwoElements(oldRenderElement, newRenderElement);
this.renderElement = currentElement;
if (this.componentDidUpdate) {
this.componentDidUpdate();
}
}
}
//类组件的本质也是函数(请参考new Class原理)，通过`isReactComponent`判断是类组件还是函数组件
Component.prototype.isReactComponent = {};
export {
Component
}
2.2. src/react/vdom.js
import { TEXT, ELEMENT, CLASS_COMPONENT, FUNCTION_COMPONENT } from './constants';
import { setProps, onlyOne, flatten } from './utils';
export function compareTwoElements(oldRenderElement, newRenderElement) {
oldRenderElement = onlyOne(oldRenderElement);
newRenderElement = onlyOne(newRenderElement);
let currentDOM = oldRenderElement.dom;//取出老的DOM节点（此处，element.dom = dom;已经做过预埋设计）
let currentElement = oldRenderElement;
if (newRenderElement == null) {
currentDOM.parentNode.removeChild(currentDOM);//新的虚拟DOM为null，删掉老节点
currentDOM = null;
} else if (oldRenderElement.type != newRenderElement.type) { // span div function class
let newDOM = createDOM(newRenderElement);//类型不同，新节点替换老节点
currentDOM.parentNode.replaceChild(newDOM, currentDOM);
currentElement = newRenderElement;
} else {//新老节点都存在，类型一样。进行 dom-diff 深度比较，比较他们的属性和子节点，并尽可能复用老节点
//TODO 这里简单模拟实现
let newDOM = createDOM(newRenderElement);
currentDOM.parentNode.replaceChild(newDOM, currentDOM);
currentElement = newRenderElement;
}
return currentElement;
}
export function createDOM(element) {
if (typeof element !== 'object') {
throw Error(`Uncaught DOMException: Failed to execute 'createElement' on 'Document': The tag name provided ('${element}') is not a valid name.`)
}
/**
* !!! element 如果是字符串或者数字，已经在迭代`children`时封装成对象
* 因此`createDOM`方法可以整体进行改造
*/
let dom;
element = onlyOne(element); // 如果是数组，只取第一个
let { $$typeof } = element;
if (!$$typeof) { // 字符串或者数字
dom = document.createTextNode(element);
} else if ($$typeof == TEXT) {
dom = document.createTextNode(element.content);
} else if ($$typeof == ELEMENT) { // 原生DOM节点
dom = createNativeDOM(element);
} else if ($$typeof == FUNCTION_COMPONENT) { // 函数组件
dom = createFunctionComponentDOM(element);
} else if ($$typeof == CLASS_COMPONENT) { // 类组件
dom = createClassComponentDOM(element);
}
/**
* `element`是ReactElement创建出来的虚拟DOM，让虚拟的DOM的`dom`属性指向真实DOM
* 这里是一个预埋设计，或者叫铺垫，通过虚拟DOM能够获取真实DOM
*/
element.dom = dom;
return dom;
}
// 创建函数组件真实的DOM对象
function createFunctionComponentDOM(element) {
//element: $$typeof, type, key, ref, props
let { type, props } = element;
/**
* function FunctionComponent(props) {
* return React.createElement('div', { id: 'counter' }, 'hello');
* }
*/
let renderElement = type(props);// type === FunctionComponent
//element 是 React.createElement(FunctionComponent, config, children); 的返回值
//element 是 FunctionComponent 的父级，当然这里不是DOM的父级，只是理解为父级
element.renderElement = renderElement; // 这里也是一个预埋设计
let dom = createDOM(renderElement);
return dom;
// 第25行`element.dom = dom;`，可以推导出: element.renderElement.dom=真实DOM
}
// 创建类组件真实的DOM对象
function createClassComponentDOM(element) {
let { type, props } = element;
/**
* class ClassCounter extends React.Component {
* constructor(props) {
* super(props);
* }
* render() {
* return React.createElement('div', { id: 'counter' }, 'hello');
* }
* }
*/
let componentInstance = new type(props);
element.componentInstance = componentInstance; // 这里也是一个预埋设计
let renderElement = componentInstance.render();
componentInstance.renderElement = renderElement; // 这里也是一个预埋设计
let dom = createDOM(renderElement);
return dom;
// 第25行`element.dom = dom;`，可以推导出: element.componentInstance.renderElement.dom=真实DOM
}
/**
let element = React.createElement('button',
{ id: 'sayHello', onClick },
'say', React.createElement('span', { onClick: spanClick, style: { color: 'red' } }, 'Hello')
);
*/
function createNativeDOM(element) {
let { type, props } = element; // div button span
let dom = document.createElement(type); //真实DOM对象
//1，创建虚拟dom的子节点
createNativeDOMChildren(dom, element.props.children);
//2，给DOM元素添加属性
setProps(dom, props);
return dom;
}
function createNativeDOMChildren(parentNode, ...children) {
let childrenNodeArr = children && flatten(children);
if (childrenNodeArr) {
for (let i = 0; i < childrenNodeArr.length; i++) {
let child = childrenNodeArr[i];
/**
* !!! 由于需要通过 element 获取 dom 元素，此处将 字符串或者数字 封装成对象
*/
if (typeof child !== 'object') { // 字符串或数字
child = childrenNodeArr[i] = { $$typeof: TEXT, type: TEXT, content: child };
}
//child会传递给element，预埋设计，跟第25行`element.dom = dom;`逻辑一样，给element添加索引
child._mountIndex = i;
let childDOM = createDOM(child);
parentNode.appendChild(childDOM);
}
}
}
export function ReactElement($$typeof, type, key, ref, props) {
let element = {
$$typeof, type, key, ref, props
};
return element;
}
3. state与事件
3.1. src/index.js
import React from './react';
import ReactDOM from './react-dom';
class Counter extends React.Component {
constructor(props) {
super(props);
this.state = { number: 0 };
}
handleClick = () => {
this.setState({ number: this.state.number + 1 });
console.log(this.state.number);//0
this.setState({ number: this.state.number + 1 });
console.log(this.state.number);//0
setTimeout(() => {
this.setState({ number: this.state.number + 1 });
console.log(this.state.number);//2
this.setState({ number: this.state.number + 1 });
console.log(this.state.number);//3
}, 10);
}
render() {
return <div id={'counter' + this.state.number} onClick={this.handleClick}>+</div>
}
}
ReactDOM.render(
<Counter />,
document.getElementById('root')
);
3.2. src/react/component.js
import { compareTwoElements } from './vdom';
//更新队列
export const updateQueue = {
updaters: [],//要执行的updater对象
isPending: false,//是否处于批量更新模式
add(updater) {
this.updaters.push(updater);
},
//需要调用batchUpdate才更新
batchUpdate(){
let { updaters } = this;
this.isPending = true;//开始更新
let updater;
while (updater = updaters.pop()) {
updater.updateComponent();//更新所有 dirty 组件
}
this.isPending = false;//更新完毕
}
};
class Updater {
constructor(componentInstance) {
this.componentInstance = componentInstance;//Updater和类组件1对1关系
this.pendingStates = [];//更新如果批量的，先把状态暂存到数组，最后更新时统一合并
this.nextProps = null;//新的属性对象
}
addState(partialState){
this.pendingStates.push(partialState);//把新状态放入数组
this.emitUpdate();
}
emitUpdate(nextProps){
this.nextProps = nextProps;
//如果有新属性对象 或者 队列处于‘休息’状态，直接更新
if (nextProps || !updateQueue.isPending) {
this.updateComponent();
} else {//否则交给队列处理
updateQueue.add(this);
}
}
updateComponent(){
let { componentInstance, pendingStates, nextProps } = this;
if (nextProps || pendingStates.length > 0) {//长度大于0，有要合并的状态
shouldUpdate(componentInstance, nextProps, this.getState());
}
}
//合并及返回新的状态
getState(){
let { componentInstance, pendingStates } = this;
let { state } = componentInstance;//老组件当前状态
if (pendingStates.length > 0) {
//迭代pendingStates，将所有状态合并到state
for (let i = 0; i < pendingStates.length; i++) {
let nextState = pendingStates[i];
if (typeof nextState === 'function') {
state = { ...state, ...nextState.call(componentInstance, state) };
} else {
state = { ...state, ...nextState };
}
}
}
pendingStates.length = 0;//合并后清空数组
return state;
}
}
//判断是否要更新
function shouldUpdate(componentInstance, nextProps, nextState) {
componentInstance.props = nextProps;//将新props赋给组件
componentInstance.state = nextState;//将新state赋给组件
if (
componentInstance.shouldComponentUpdate &&
!componentInstance.shouldComponentUpdate(nextProps, nextState)
) {
//如果shouldComponentUpdate返回false，则不更新
return false;
}
componentInstance.forceUpdate();//让组件强制更新
}
class Component {
constructor(props) {
this.props = props;
this.$updater = new Updater(this); //this 就是类组件的实例
this.state = {}; // 当前状态
this.nextProps = null; // 下一个属性对象
}
//批量更新 partial，状态可能会被合并
setState(partialState) {
this.$updater.addState(partialState);
}
forceUpdate(){//进行组件更新
console.log('force')
let { props, state, renderElement: oldRenderElement } = this;
if (this.componentWillUpdate) {
this.componentWillUpdate();
}
let newRenderElement = this.render();
let currentElement = compareTwoElements(oldRenderElement, newRenderElement);
this.renderElement = currentElement;
if (this.componentDidUpdate) {
this.componentDidUpdate();
}
}
}
//类组件的本质也是函数(请参考new Class原理)，通过`isReactComponent`判断是类组件还是函数组件
Component.prototype.isReactComponent = {};
export {
Component
}
3.3. src/react/event.js
import { updateQueue } from './component';
/**
* React通过，类似于`事件委托`机制，将事件绑定到document上；
* 并把事件回调函数，以`eventStore`的形式，挂载到对应的真实DOM上
* @param {*} dom 要绑定事件的DOM节点
* @param {*} eventType 事件类型 onClick
* @param {*} listener 事件处理函数
*/
export function addEvent(dom, eventType, listener) {
eventType = eventType.toLowerCase(); // onClick 作为key，转换成 onclick
//在要绑定的DOM节点上挂载一个对象，准备存放监听函数
let eventStore = dom.eventStore || (dom.eventStore = {});
//eventStore.onClick = () => {console.log('this is onClick')}
eventStore[eventType] = listener;
/**
* 这里可以做兼容处理，比如兼容IE、Chrome、Firefox等等
*/
// true是捕获阶段，处理事件； false是冒泡阶段，处理事件
document.addEventListener(eventType.slice(2), dispatchEvent, false);
}
let syntheticEvent;//合成对象，可以复用，减少垃圾回收，提高性能
function dispatchEvent(event) {
let { type, target } = event;//type->click target->button
let eventType = 'on' + type; //onclick
syntheticEvent = getSyntheticEvent(event);
//事件监听函数执行之前，进入批量更新模式
updateQueue.isPending = true;
// 模拟冒泡过程
while(target) {
let {eventStore} = target;
let listener = eventStore && eventStore[eventType];//onClick
if (listener) {
listener.call(target, syntheticEvent);
}
target = target.parentNode;
}
//所有监听函数执行完毕，清掉所有属性
for (const key in syntheticEvent) {
if (syntheticEvent.hasOwnProperty(key)) {
delete syntheticEvent[key];
}
}
//事件处理函数执行完成，关掉批量更新模式
updateQueue.isPending = false;
//执行批量更新，把缓存的updater全部执行
updateQueue.batchUpdate();
}
//如果执行了persist，就让syntheticEvent指向新对象
function persist() {
syntheticEvent = {};
syntheticEvent.__proto__.persist = persist;
}
function getSyntheticEvent(nativeEvent){
if (!syntheticEvent) {
syntheticEvent = {};
syntheticEvent.__proto__.persist = persist;
}
syntheticEvent.nativeEvent = nativeEvent;
syntheticEvent.currentTarget = nativeEvent.target;
//把原生事件对象上的方法和属性都拷贝到合成对象上
for (let key in nativeEvent) {
if (typeof nativeEvent[key] === 'function') {
syntheticEvent[key] = nativeEvent[key].bind(nativeEvent); //绑定this
} else {
syntheticEvent[key] = nativeEvent[key];
}
}
return syntheticEvent;
}
3.4. 测试结果
0
0
force
force
2
force
3
3.5. setState函数形式
import React from './react';
import ReactDOM from './react-dom';
class Counter extends React.Component {
constructor(props) {
super(props);
this.state = { number: 0 };
}
handleClick = () => {
this.setState((state) => ({ number: state.number + 1 }));
console.log(this.state.number);//0
this.setState((state) => ({ number: state.number + 1 }));
console.log(this.state.number);//0
setTimeout(() => {
this.setState((state) => ({ number: state.number + 1 }));
console.log(this.state.number);//3
this.setState((state) => ({ number: state.number + 1 }));
console.log(this.state.number);//4
}, 10);
}
render() {
return <div id={'counter' + this.state.number} onClick={this.handleClick}>+</div>
}
}
ReactDOM.render(
<Counter />,
document.getElementById('root')
);
3.5. 测试结果
0
0
force
force
3
force
4
4. 替换相同类型
4.1. src/index.js
import React from './react';
import ReactDOM from './react-dom';
class Counter extends React.Component {
constructor(props) {
super(props);
this.state = { number: 0 };
}
handleClick = () => {
this.setState((state) => ({ number: state.number + 1 }));
}
render() {
return (
<div id={'counter' + this.state.number}>
<p>{this.state.number}</p>
<button onClick={this.handleClick}>+</button>
</div>
)
}
}
ReactDOM.render(
<Counter />,
document.getElementById('root')
);
4.2. src/react/vdom.js
import { TEXT, ELEMENT, CLASS_COMPONENT, FUNCTION_COMPONENT } from './constants';
import { setProps, onlyOne, flatten, patchProps } from './utils';
export function compareTwoElements(oldRenderElement, newRenderElement) {
oldRenderElement = onlyOne(oldRenderElement);
newRenderElement = onlyOne(newRenderElement);
let currentDOM = oldRenderElement.dom;//取出老的DOM节点（此处，element.dom = dom;已经做过预埋设计）
let currentElement = oldRenderElement;
if (newRenderElement == null) {
currentDOM.parentNode.removeChild(currentDOM);//新的虚拟DOM为null，删掉老节点
currentDOM = null;
} else if (oldRenderElement.type != newRenderElement.type) { // span div function class
let newDOM = createDOM(newRenderElement);//类型不同，新节点替换老节点
currentDOM.parentNode.replaceChild(newDOM, currentDOM);
currentElement = newRenderElement;
} else {
//新老节点都存在，类型一样。进行 dom-diff 深度比较，比较他们的属性和子节点，并尽可能复用老节点
updateElement(oldRenderElement, newRenderElement);
}
return currentElement;
}
// *** 如果是`函数组件`或`类组件`,`oldElement`就是`oldRenderElement`
// renderElement 是函数组件执行后 或 类组件调用render后返回的虚拟DOM，虚拟DOM是由React.createElement创建的
function updateElement(oldElement, newElement) {
let currentDOM = newElement.dom = oldElement.dom;
if (oldElement.$$typeof === TEXT && newElement.$$typeof === TEXT) {
if (oldElement.content !== newElement.content) {
currentDOM.textContent = newElement.content;
}
} else if (oldElement.$$typeof === ELEMENT) {// div span p
updateDOMProperties(currentDOM, oldElement.props, newElement.props);
}
}
function updateDOMProperties(dom, oldProps, newProps) {
patchProps(dom, oldProps, newProps);
}
export function createDOM(element) {
if (typeof element !== 'object') {
throw Error(`Uncaught DOMException: Failed to execute 'createElement' on 'Document': The tag name provided ('${element}') is not a valid name.`)
}
/**
* !!! element 如果是字符串或者数字，已经在迭代`children`时封装成对象
* 因此`createDOM`方法可以整体进行改造
*/
let dom;
element = onlyOne(element); // 如果是数组，只取第一个
let { $$typeof } = element;
if (!$$typeof) { // 字符串或者数字
dom = document.createTextNode(element);
} else if ($$typeof == TEXT) {
dom = document.createTextNode(element.content);
} else if ($$typeof == ELEMENT) { // 原生DOM节点
dom = createNativeDOM(element);
} else if ($$typeof == FUNCTION_COMPONENT) { // 函数组件
dom = createFunctionComponentDOM(element);
} else if ($$typeof == CLASS_COMPONENT) { // 类组件
dom = createClassComponentDOM(element);
}
/**
* `element`是ReactElement创建出来的虚拟DOM，让虚拟的DOM的`dom`属性指向真实DOM
* 这里是一个预埋设计，或者叫铺垫，通过虚拟DOM能够获取真实DOM
*/
element.dom = dom;
return dom;
}
// 创建函数组件真实的DOM对象
function createFunctionComponentDOM(element) {
//element: $$typeof, type, key, ref, props
let { type, props } = element;
/**
* function FunctionComponent(props) {
* return React.createElement('div', { id: 'counter' }, 'hello');
* }
*/
let renderElement = type(props);// type === FunctionComponent
//element 是 React.createElement(FunctionComponent, config, children); 的返回值
//element 是 FunctionComponent 的父级，当然这里不是DOM的父级，只是理解为父级
element.renderElement = renderElement; // 这里也是一个预埋设计
let dom = createDOM(renderElement);
return dom;
// 第25行`element.dom = dom;`，可以推导出: element.renderElement.dom=真实DOM
}
// 创建类组件真实的DOM对象
function createClassComponentDOM(element) {
let { type, props } = element;
/**
* class ClassCounter extends React.Component {
* constructor(props) {
* super(props);
* }
* render() {
* return React.createElement('div', { id: 'counter' }, 'hello');
* }
* }
*/
let componentInstance = new type(props);
element.componentInstance = componentInstance; // 这里也是一个预埋设计
let renderElement = componentInstance.render();
componentInstance.renderElement = renderElement; // 这里也是一个预埋设计
let dom = createDOM(renderElement);
return dom;
// 第25行`element.dom = dom;`，可以推导出: element.componentInstance.renderElement.dom=真实DOM
}
/**
let element = React.createElement('button',
{ id: 'sayHello', onClick },
'say', React.createElement('span', { onClick: spanClick, style: { color: 'red' } }, 'Hello')
);
*/
function createNativeDOM(element) {
let { type, props } = element; // div button span
let dom = document.createElement(type); //真实DOM对象
//1，创建虚拟dom的子节点
createNativeDOMChildren(dom, element.props.children);
//2，给DOM元素添加属性
setProps(dom, props);
return dom;
}
function createNativeDOMChildren(parentNode, ...children) {
let childrenNodeArr = children && flatten(children);
if (childrenNodeArr) {
for (let i = 0; i < childrenNodeArr.length; i++) {
let child = childrenNodeArr[i];
/**
* !!! 由于需要通过 element 获取 dom 元素，此处将 字符串或者数字 封装成对象
*/
if (typeof child !== 'object') { // 字符串或数字
child = childrenNodeArr[i] = { $$typeof: TEXT, type: TEXT, content: child };
}
//child会传递给element，预埋设计，跟第25行`element.dom = dom;`逻辑一样，给element添加索引
child._mountIndex = i;
let childDOM = createDOM(child);
parentNode.appendChild(childDOM);
}
}
}
export function ReactElement($$typeof, type, key, ref, props) {
let element = {
$$typeof, type, key, ref, props
};
return element;
}
在
updateElement方法中:
如果是函数组件或类组件,oldElement就是oldRenderElement,renderElement是函数组件执行后 或 类组件调用render后返回的虚拟DOM,
虚拟DOM是由React.createElement创建的.
4.3. src/react/utils.js
import { addEvent } from './event';
export function setProps(dom, props) {
for (let key in props) {
if (key != 'children') {
let value = props[key];
setProp(dom, key, value);
}
}
}
//老有新没有=>删除 老有新有=>更新 老没有新有=>添加
export function patchProps(dom, oldProps, newProps) {
//1,删除老有新没有
for (const key in oldProps) {
if (key !== 'children') {//children单独处理
if (!newProps.hasOwnProperty(key)) {
dom.removeAttribute(key);//新的不存在,删除
}
}
}
//2,新增及更新,新有
for (let key in newProps) {
if (key !== 'children') {//children单独处理
setProp(dom, key, newProps[key]);
}
}
}
function setProp(dom, key, value) {
if (/^on/.test(key)) {
addEvent(dom, key, value);
} else if (key === 'style') {
for (const styleName in value) {
dom.style[styleName] = value[styleName];
}
} else {
dom.setAttribute(key, value);
}
}
export function onlyOne(obj) {
return Array.isArray(obj) ? obj[0] : obj;
}
// 打平任意多维数组，避免深度克隆
export function flatten(arr) {
return arr.reduce((prev, curr, index) => {
if (Array.isArray(curr)) {
prev = prev.concat(flatten(curr));
} else {
prev = prev.concat(curr);
}
return prev;
}, []);
}
4.4. src/react/event.js
import { updateQueue } from './component';
/**
* React通过，类似于`事件委托`机制，将事件绑定到document上；
* 并把事件回调函数，以`eventStore`的形式，挂载到对应的真实DOM上
* @param {*} dom 要绑定事件的DOM节点
* @param {*} eventType 事件类型 onClick
* @param {*} listener 事件处理函数
*/
export function addEvent(dom, eventType, listener) {
eventType = eventType.toLowerCase(); // onClick 作为key，转换成 onclick
//在要绑定的DOM节点上挂载一个对象，准备存放监听函数
let eventStore = dom.eventStore || (dom.eventStore = {});
//eventStore.onClick = () => {console.log('this is onClick')}
eventStore[eventType] = listener;
/**
* 这里可以做兼容处理，比如兼容IE、Chrome、Firefox等等
*/
// true是捕获阶段，处理事件； false是冒泡阶段，处理事件
document.addEventListener(eventType.slice(2), dispatchEvent, false);
}
let syntheticEvent;//合成对象，可以复用，减少垃圾回收，提高性能
function dispatchEvent(event) {
let { type, target } = event;//type->click target->button
let eventType = 'on' + type; //onclick
syntheticEvent = getSyntheticEvent(event);
//事件监听函数执行之前，进入批量更新模式
updateQueue.isPending = true;
// 模拟冒泡过程
while (target) {
let { eventStore } = target;
let listener = eventStore && eventStore[eventType];//onClick
if (listener) {
listener.call(target, syntheticEvent);
}
target = target.parentNode;
}
//所有监听函数执行完毕，清掉所有属性
for (const key in syntheticEvent) {
if (syntheticEvent.hasOwnProperty(key)) {
delete syntheticEvent[key];
}
}
//事件处理函数执行完成，关掉批量更新模式
updateQueue.isPending = false;
//执行批量更新，把缓存的updater全部执行
updateQueue.batchUpdate();
}
//如果执行了persist，就让syntheticEvent指向新对象
function persist() {
syntheticEvent = {};
/**
* 下一行写法错误:
* 根据原型链: obj.__proto__ 指向 Object.prototype;
* 如果 obj.__proto__.abc = abc 等价于 Object.prototype.abc = abc;
* 这是具有破坏性的,这样执行后每个 Object() 实力对象，都将具有 __proto__ 都具有了 abc 属性;
* for (key in obj) {
* console.log(key); // abc
* }
* 该for循环说明了,for in,可以找到在__proto__上自定义的属性。（用浏览器观察__proto__时,会发现自定义属性颜色更鲜艳）
*/
// syntheticEvent.__proto__.persist = persist;
Object.setPrototypeOf(syntheticEvent, { persist }); //等价于 syntheticEvent.__proto__ = { persist };
}
function getSyntheticEvent(nativeEvent) {
if (!syntheticEvent) {
persist();
}
syntheticEvent.nativeEvent = nativeEvent;
syntheticEvent.currentTarget = nativeEvent.target;
//把原生事件对象上的方法和属性都拷贝到合成对象上
for (let key in nativeEvent) {
if (typeof nativeEvent[key] === 'function') {
syntheticEvent[key] = nativeEvent[key].bind(nativeEvent); //绑定this
} else {
syntheticEvent[key] = nativeEvent[key];
}
}
return syntheticEvent;
}
原型链的错误写法分析:
错误写法:syntheticEvent.__proto__.persist = persist;
原理说明:
var obj = {}; obj.__proto__ === Object.prototype;//true
obj.__proto__.abc = function abc(){};=>Object.prototype.abc === abc;
- 这样是具有破坏性的，这样执行后，每个
Object的实例对象的__proto__都具有了abc属性
for (key in obj) {console.log(key);//abc}
- 该for循环说明了,
for in,可以找到在__proto__上自定义的属性- 用浏览器观察
__proto__时,会发现自定义属性颜色更鲜艳
5. 类组件与函数组件
5.1. src/index.js
import React from './react';
import ReactDOM from './react-dom';
//有两个虚拟DOM <FunctionCounter/> <div id={'counter'}/>
function FunctionCounter(props) {
return (
<div id={'counter' + props.number} >
<p>{props.number}</p>
<button onClick={props.handleClick}>+</button>
</div>
)
}
class ClassCounter extends React.Component {
render() {
return (
<div id={'counter' + this.props.number} >
<p>{this.props.number}</p>
<button onClick={this.props.handleClick}>+</button>
</div>
)
}
}
class Counter extends React.Component {
constructor(props) {
super(props);
this.state = { number: 0 };
}
handleClick = () => {
this.setState((state) => ({ number: state.number + 1 }));
}
render() {
return (
/*
<div id={'counter' + this.state.number} >
<p > {this.state.number}</p>
<button onClick={this.handleClick}>+</button>
</div>
*/
<FunctionCounter number={this.state.number} handleClick={this.handleClick} />
//<ClassCounter number={this.state.number} handleClick={this.handleClick} />
//React.createElement(ClassCounter, { number: this.state.number, handleClick: this.handleClick })
)
}
}
//{type:FunctionCounter,props:{number:0}}
ReactDOM.render(
<Counter />,
document.getElementById('root')
);
5.2. src/react/vdom.js
import { TEXT, ELEMENT, CLASS_COMPONENT, FUNCTION_COMPONENT } from './constants';
import { setProps, onlyOne, flatten, patchProps } from './utils';
export function compareTwoElements(oldRenderElement, newRenderElement) {
oldRenderElement = onlyOne(oldRenderElement);
newRenderElement = onlyOne(newRenderElement);
let currentDOM = oldRenderElement.dom;//取出老的DOM节点（此处，element.dom = dom;已经做过预埋设计）
let currentElement = oldRenderElement;
if (newRenderElement == null) {
currentDOM.parentNode.removeChild(currentDOM);//新的虚拟DOM为null，删掉老节点
currentDOM = null;
} else if (oldRenderElement.type != newRenderElement.type) { // span div function class
let newDOM = createDOM(newRenderElement);//类型不同，新节点替换老节点
currentDOM.parentNode.replaceChild(newDOM, currentDOM);
currentElement = newRenderElement;
} else {
//新老节点都存在，类型一样。进行 dom-diff 深度比较，比较他们的属性和子节点，并尽可能复用老节点
updateElement(oldRenderElement, newRenderElement);
}
return currentElement;
}
// *** 如果是`函数组件`或`类组件`,`oldElement`就是`oldRenderElement`
// renderElement 是函数组件执行后 或 类组件调用render后返回的虚拟DOM，虚拟DOM是由React.createElement创建的
function updateElement(oldElement, newElement) {
let currentDOM = newElement.dom = oldElement.dom;
if (oldElement.$$typeof === TEXT && newElement.$$typeof === TEXT) {
if (oldElement.content !== newElement.content) {
currentDOM.textContent = newElement.content;
}
} else if (oldElement.$$typeof === ELEMENT) {// div span p
updateDOMProperties(currentDOM, oldElement.props, newElement.props);
} else if (oldElement.$$typeof === FUNCTION_COMPONENT) {// 函数组件
updateFunctionComponent(oldElement, newElement);
} else if (oldElement.$$typeof === CLASS_COMPONENT) {// 类组件
updateClassComponent(oldElement, newElement);
}
}
function updateDOMProperties(dom, oldProps, newProps) {
patchProps(dom, oldProps, newProps);
}
//类组件element.componentInstance.renderElement.dom=真实DOM
function updateClassComponent(oldElement, newElement) {
let componentInstance = oldElement.componentInstance;
let updater = componentInstance.$updater;
let nextProps = newElement.props;
updater.emitUpdate(nextProps);
}
//函数组件element.renderElement.dom=真实DOM
function updateFunctionComponent(oldElement, newElement) {
let oldRenderElement = oldElement.renderElement;
let newRenderElement = newElement.type(newElement.props);
let currentDOM = compareTwoElements(oldRenderElement, newRenderElement);
newElement.renderElement = currentDOM;//更新之后，重新挂载
}
export function createDOM(element) {
if (typeof element !== 'object') {
throw Error(`Uncaught DOMException: Failed to execute 'createElement' on 'Document': The tag name provided ('${element}') is not a valid name.`)
}
/**
* !!! element 如果是字符串或者数字，已经在迭代`children`时封装成对象
* 因此`createDOM`方法可以整体进行改造
*/
let dom;
element = onlyOne(element); // 如果是数组，只取第一个
let { $$typeof } = element;
if (!$$typeof) { // 字符串或者数字
dom = document.createTextNode(element);
} else if ($$typeof == TEXT) {
dom = document.createTextNode(element.content);
} else if ($$typeof == ELEMENT) { // 原生DOM节点
dom = createNativeDOM(element);
} else if ($$typeof == FUNCTION_COMPONENT) { // 函数组件
dom = createFunctionComponentDOM(element);
} else if ($$typeof == CLASS_COMPONENT) { // 类组件
dom = createClassComponentDOM(element);
}
/**
* `element`是ReactElement创建出来的虚拟DOM，让虚拟的DOM的`dom`属性指向真实DOM
* 这里是一个预埋设计，或者叫铺垫，通过虚拟DOM能够获取真实DOM
*/
element.dom = dom;
return dom;
}
// 创建函数组件真实的DOM对象
function createFunctionComponentDOM(element) {
//element: $$typeof, type, key, ref, props
let { type, props } = element;
/**
* function FunctionComponent(props) {
* return React.createElement('div', { id: 'counter' }, 'hello');
* }
*/
let renderElement = type(props);// type === FunctionComponent
//element 是 React.createElement(FunctionComponent, config, children); 的返回值
//element 是 FunctionComponent 的父级，当然这里不是DOM的父级，只是理解为父级
element.renderElement = renderElement; // 这里也是一个预埋设计
let dom = createDOM(renderElement);
return dom;
// 第25行`element.dom = dom;`，可以推导出: element.renderElement.dom=真实DOM
}
// 创建类组件真实的DOM对象
function createClassComponentDOM(element) {
let { type, props } = element;
/**
* class ClassCounter extends React.Component {
* constructor(props) {
* super(props);
* }
* render() {
* return React.createElement('div', { id: 'counter' }, 'hello');
* }
* }
*/
let componentInstance = new type(props);
element.componentInstance = componentInstance; // 这里也是一个预埋设计
let renderElement = componentInstance.render();
componentInstance.renderElement = renderElement; // 这里也是一个预埋设计
let dom = createDOM(renderElement);
return dom;
// 第25行`element.dom = dom;`，可以推导出: element.componentInstance.renderElement.dom=真实DOM
}
/**
let element = React.createElement('button',
{ id: 'sayHello', onClick },
'say', React.createElement('span', { onClick: spanClick, style: { color: 'red' } }, 'Hello')
);
*/
function createNativeDOM(element) {
let { type, props } = element; // div button span
let dom = document.createElement(type); //真实DOM对象
//1，创建虚拟dom的子节点
createNativeDOMChildren(dom, element.props.children);
//2，给DOM元素添加属性
setProps(dom, props);
return dom;
}
function createNativeDOMChildren(parentNode, ...children) {
let childrenNodeArr = children && flatten(children);
if (childrenNodeArr) {
for (let i = 0; i < childrenNodeArr.length; i++) {
let child = childrenNodeArr[i];
/**
* !!! 由于需要通过 element 获取 dom 元素，此处将 字符串或者数字 封装成对象
*/
if (typeof child !== 'object') { // 字符串或数字
child = childrenNodeArr[i] = { $$typeof: TEXT, type: TEXT, content: child };
}
//child会传递给element，预埋设计，跟第25行`element.dom = dom;`逻辑一样，给element添加索引
child._mountIndex = i;
let childDOM = createDOM(child);
parentNode.appendChild(childDOM);
}
}
}
export function ReactElement($$typeof, type, key, ref, props) {
let element = {
$$typeof, type, key, ref, props
};
return element;
}
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