搭建学习环境
npm install -g parcel-bundler
package.json
{
"name": "myReact",
"version": "1.0.0",
"description": "",
"main": "index.js",
"scripts": {
"start": "parcel index.html",
"test": "echo \"Error: no test specified\" && exit 1"
},
"keywords": [],
"author": "",
"license": "ISC",
"dependencies": {
"babel-preset-env": "^1.6.1",
"babel-preset-es2015": "^6.24.1",
"parcel-bundler": "^1.6.2"
},
"devDependencies": {
"babel-plugin-transform-react-jsx": "^6.24.1"
}
}
支持 JSX
在 js 文件中我们是不能写 jsx 语法的，必须使用一种 babel 插件 transform-react-jsx 才能使用。
新建.babelrc
{
"presets": ["env"],
"plugins": [
["transform-react-jsx", {
"pragma": "createElement"
}]
]
}
实现一个 createElement
.babelrc 文件中使用了transform-react-jsx 插件，告诉babel 解析 jsx 需要 createElement方法，也就是 babel 编译后的React.createElement
createElement 有三个参数
function createElement(type, props, ...args) {
props = props || {}
let children = []
for (let i = 0; i < args.length; i++) {
if (Array.isArray(args[i])) {
children = [ ...children, ...args[i] ]
} else {
children = [ ...children, args[i] ]
}
}
return { type, props, children }
}
然后我们来试验下createElement 结果
import { createElement } from './src/react'
const React = {}
React.createElement = createElement
React.Component = class Component {}
class App extends React.Component {
render() {
return (
<div>
<span>App</span>
<span>component</span>
</div>
)
}
}
const app = new App().render()
console.log(app)
new App().render() 这种格式跟 react 组件区别有些大，再实现一个renderVDOM(<App />) 的格式
function reactVDOM(vnode) {
if (typeof vnode === 'string') return vnode // 文本节点
if (typeof vnode.type === 'string') { // type 为标签名 - dom节点
let ret = {
type: ret.type,
props: ret.props,
children: []
}
for (let i = 0; i < vnode.children.length; i++) {
ret.children.push(reactVDOM(vnode.children[i])) // 递归children
}
return ret
}
if (typeof vnode.type === 'function') { // type 为 class 组件
let func = vnode.type
let inst = new func(vnode.props) // 把 props 传入
let innerVNODE = inst.render()
return reactVDOM(innerVNODE) // 递归渲染后的组件
}
}
import { createElement } from './src/react'
import { renderVDOM } from './src/renderVDOM'
const React = {}
React.createElement = createElement
React.Component = class Component {}
class App extends React.Component {
render() {
return (
<div>
<span>App</span>
<span>component</span>
</div>
)
}
}
const app = renderVDOM(<App />)
console.log(app) // 与 new App().render() 一样
父子组件
class ChildrenChild extends React.Component {
render() {
return (
<div>
children-child
</div>
)
}
}
class Children extends React.Component {
render() {
return (
<div>
children
<ChildrenChild />
</div>
)
}
}
class App extends React.Component {
render() {
return (
<div>
<span>App</span>
<span>component</span>
<Children />
</div>
)
}
}
const app = renderVDOM(<App />)
结果中组件的文本内容、dom、组件实例都在children 数组里，React.render 时只需要识别这些children 就可以做到真实渲染
实现 render
改写 renderVDMO 加入真实 dom 操作
function render(vnode, parent) {
let dom
if (typeof vnode === 'string') { // 文本节点直接渲染
dom = document.createTextNode(vnode)
parent.appendChild(dom)
}
if (typeof vnode.type === 'string') { // dom 节点
dom = document.createElement(vnode.type)
setAttrs(dom, vnode.props) // props 已经被createElement 解析成对象
parent.appendChild(dom)
for(let i = 0; i < vnode.children.length; i++) {
render(vnode.children[i], dom) // 递归 render children
}
}
if (typeof vnode.type === 'function') { // class 组件
let func = vnode.type
let inst = new func(vnode.props) // props 已经被createElement 解析成对象
let innerVNode = inst.render()
render(innerVNode, parent)
}
}
function setAttrs(dom, props) {
Object.keys(props).forEach(k => {
const v = props[k]
if (k === 'className') {
dom.setAttribute('class', v)
return
}
if (k === 'style') {
if (typeof v === 'string') dom.style.cssText = v
if (typeof v === 'object') {
for (let i in v) {
dom.style[i] = v[i]
}
}
return
}
if (k[0] === 'o' && k[1] === 'n') { // onClick of onClickCapture
const capture = k.indexOf('Capture') !== -1
dom.addEventListener(k.replace('Capture', '').substring(2).toLowerCase(), v, capture)
return
}
dom.setAttribute(k, v)
})
}
把上面例子换一下
// app.js
class ChildrenChild extends React.Component {
render() {
return (
<div>
children-child
</div>
)
}
}
class Children extends React.Component {
render() {
return (
<div>
children
<ChildrenChild />
</div>
)
}
}
class App extends React.Component {
render() {
return (
<div>
<span>App</span>
<span>component</span>
<Children />
</div>
)
}
}
render(<App />, document.getElementById('app'))
// index.html
<body>
<div id="app"></div>
<script src="./app.js"></script>
</body>
结果
实现props 和state
class Color extends React.Component {
render() {
return (
<div style={{ color: this.props.color }}>color is: {this.props.color}</div>
)
}
}
const colorArr = ['red', 'blue', 'black', 'green', 'gray']
class App extends React.Component {
constructor(props) {
super(props)
this.state = {
color: 'black'
}
}
handleClick() {
console.log("handleClick")
this.setState({
color: colorArr[Math.random() * 5 | 0]
})
}
render() {
return (
<div onClick={this.handleClick.bind(this)}>
<Color color={this.state.color} />
</div>
)
}
}
render(<App />, document.getElementById('app'))
目的: 我们要通过点击 App 组件中的元素来改变 Color 文字的颜色
步骤: 把新的state 传入 this.setState 来更新组件 - 调用render 方法
setState
export default class Component {
constructor(props) {
this.props = props
}
setState(state) {
setTimeout(() => {
this.state = state
// ...render()
})
}
}
回忆 render 函数有两个参数，vnode， parent，vnode 我们可以使用 this.render() 获取当前组件，但我们要知道需要更新dom 内容的 parent 就需要在首次render 时记录。
改写 render
给render 增加参数，comp(当前更新组件)， olddom(当前组件曾经的dom)
拿首次渲染举例: parent - document.getElementById('app'), comp - <App />, olddom - 当App组件更新时就是App 首次渲染的dom
export function render(vnode, parent, comp, olddom) {
let dom
if (typeof vnode === 'string') { // 文本节点直接渲染
dom = document.createTextNode(vnode)
comp && (comp.__rendered = dom)
if (olddom) parent.replaceChild(dom, olddom)
else parent.appendChild(dom)
}
if (typeof vnode.type === 'string') { // dom 节点
dom = document.createElement(vnode.type)
comp && (comp.__rendered = dom)
setAttrs(dom, vnode.props) // props 已经被createElement 解析成对象
if (olddom) parent.replaceChild(dom, olddom)
else parent.appendChild(dom)
for(let i = 0; i < vnode.children.length; i++) {
render(vnode.children[i], dom, null, null) // 递归 render children
}
}
if (typeof vnode.type === 'function') { // class 组件
let func = vnode.type
let inst = new func(vnode.props) // props 已经被createElement 解析成对象
comp && (comp.__rendered = inst) // 这里记录的是 Component 实例
let innerVNode = inst.render()
render(innerVNode, parent, inst, olddom)
}
}
在这里我们每次render 的时候都会判断这次render 是否是class 组件触发的render，如果是组件触发的render 我们就会在这个组件comp 上增加 __rendered 记录当前渲染的 dom 或 当前渲染的组件 (组件追溯到顶层也是dom) ，这时候我们需要一个方法来获得olddom
function getDOM (comp) {
let rendered = comp.__rendered
while (rendered instanceof Component) {
rendered = rendered.__rendered
}
return rendered
}
实现 setState
import { getDOM } from './util'
import { render } from './render'
export default class Component {
constructor(props) {
this.props = props
}
setState(state) {
setTimeout(() => {
this.state = state
const vnode = this.render()
let olddom = getDOM(this) // 获取渲染此实例的 olddom
render(vnode, olddom.parentNode, this, olddom)
})
}
}
实现效果
import { render, createElement, Component } from './src/code1/react'
const React = {}
React.createElement = createElement
React.Component = Component
class Color extends React.Component {
render() {
return (
<div style={{ color: this.props.color }}>color is: {this.props.color}</div>
)
}
}
const colorArr = ['red', 'blue', 'black', 'green', 'gray']
class App extends React.Component {
constructor(props) {
super(props)
this.state = {
color: 'black'
}
}
handleClick() {
console.log("handleClick")
this.setState({
color: colorArr[Math.random() * 5 | 0]
})
}
render() {
return (
<div onClick={this.handleClick.bind(this)}>
<Color color={this.state.color} />
</div>
)
}
}
render(<App />, document.getElementById('app'))
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