内容简介:3. ReactDom.render(vnode,root)会将其渲染出到页面root中:4. ReactDom.render原理简析:函数声明组件存在一些问题:
import React from 'react' import ReactDom from 'react-dom' let el=<h1><span>hello</span><span>wrold</span></h1> console.log(el) ReactDom.render(el,window.root); 复制代码
- 利用babel中的babel-preset-react进行转译,调用React.createElement(type,props,children)生成一个虚拟dom节点:
- React.createElement原理简析:
function createElement(type,props,children){ let obj={}; obj.type=type; obj.props={}; obj.props.children=null; for(let key in props){ obj.props[key]=props[key] } children.forEach(child => { let {type,props,subchildren} = child obj.props.children.push(createElement(type,props,subchildren)) }) return obj } 复制代码
3. ReactDom.render(vnode,root)会将其渲染出到页面root中:
4. ReactDom.render原理简析:
function render(vnode,container){ if(typeof vnode ==='string') return container.appendChild(document.createTextNode(vnode)); let{type,props} = vnode; let tag = document.createElement(type); for(let key in props){ if(key==='children'){ Array.from(props[key]).forEach(child => { render(child,tag) }); }else{ tag.setAttribute(key,props[key]); } } container.appendChild(tag); } 复制代码
react组件
函数声明组件
- 函数式声明组件:函数返回一个JSX语法的vnode
import React from 'react' import ReactDom from 'react-dom' function test(){ let state = { title:'标题', context:'内容' } return ( <div> <h3>{state.title}</h3> <p>{state.context}</p> </div> ) } ReactDom.render( <div> {test()} {test()} {test()} </div>,window.root); 复制代码
- 将上面的函数声明组件进行一定的包装
import React from 'react' import ReactDom from 'react-dom' function Test(props){ let state={ title:"标题" } return ( <div> <h3>{state.title}</h3> <p>{props.context}</p> </div> ) } ReactDom.render( <div> <Test context='123'></Test> <Test context='456'></Test> <Test context='789'></Test> </div>,window.root); 复制代码
函数声明组件存在一些问题:
- 没有this
- 没有状态,state无法进行动态更改
- 没有生命周期
类组件
类组件消除了函数声明组件的问题,也是现在写react的正常语法。
import React, { Component } from 'react'; import ReactDOM, { render } from 'react-dom'; import PropTypes from 'prop-types'; //属性校验插件 class Clock extends Component { state = { time: new Date().toLocaleString() } static propTypes = { name: PropTypes.string.isRequired //name必填,校验是否填写name属性 } // 组件挂载后调用 componentDidMount() { this.timer = setInterval(() => { // 只会覆盖以前的属性类似 Object.assign() this.setState({ time: new Date().toLocaleString() }) }, 1000) } handleClick = () => { //箭头函数,this用最外层的this,指向当前组件 ReactDOM.unmountComponentAtNode(window.root) } // 组件卸载前调用,一般用于解绑事件和方法 componentWillUnmount() { clearInterval(this.timer) } // 默认渲染这个组件会调用render方法 // 只是在上面函数式声明基础上包了一层函数,这样可以控制其执行时间,添加声明周期 render() { let {name} = this.props //一般会解构props return <div> {name} <span>{this.state.time}</span> <button onClick={this.handleClick}>删除</button> </div> } } render(<Clock name='test-clock'/>, window.root); 复制代码
react 生命周期
// React16.3 推出了新的声明周期 import React, { Component } from 'react'; import ReactDOM from 'react-dom'; class Counter extends Component { static defaultProps = { a: 1 } state = { num: 0 } constructor(props) { console.log('parent-constructor') super(); } // react16.3中标识了这个方法会被废弃掉 // 后期有需要的话 可以放在constructor中替代掉 componentWillMount() { console.log('parent-componentWillMount'); } // react的性能优化 immutablejs shouldComponentUpdate(){ console.log('parent-shouldComponentUpdate'); return true } componentWillReceiveProps(){ console.log('parent-componentWillReceiveProps'); } componentWillUpdate(){ console.log('parent-componentWillUpdate'); } componentDidUpdate() { console.log('parent-componentDidUpdate'); } handleClick = () => { this.setState({ num: this.state.num + 0 }); } render() { console.log('parent-render'); return <div> <button onClick={this.handleClick}>+</button> {this.state.num} <ChildCounter n={this.state.num}></ChildCounter> </div> } componentDidMount() { console.log('parent-didmount'); } componentWillUnmount() { console.log('parent-组件卸载') } } class ChildCounter extends Component{ componentWillMount(){ console.log('child-componentWillMount') } render(){ console.log('child-render'); return <div>child counter {this.props.n}</div> } componentDidMount() { console.log('child-componentDidMount') } shouldComponentUpdate(){ console.log('child-shouldComponentUpdate'); return true } componentWillUpdate(){ console.log('child-componentWillUpdate'); } componentDidUpdate() { console.log('child-componentDidUpdate'); } //16.3中这个方法废弃了 componentWillReceiveProps(){ console.log('child-componentWillReceiveProps'); } } ReactDOM.render(<Counter></Counter>, window.root); 复制代码
- 初次渲染时打印的结果为:
- 组件状态更新时打印的结果为: 从上面可以得出以下结论:
- 生命周期分为初始化生命周期和组件运行生命周期,初始化生命周期为:constructor->componentWillMount->render->componentDidMount
- 组件运行生命周期为:(存在props时:componentWillReceiveProps)->shouldComponentUpdate->componentWillUpdate->render->componentDidUpdate
- 子组件的生命周期嵌在父组件render后,DidMount和DidUpdate前
- shouldComponentUpdate返回false,组件将不会更新
- 只有componentWillReceiveProps、componentWillMount、componentDidMount中可以调用setState,不应该在componentWillReceiveProps中调用setState(但是大家还是这么用)
受控组件和非受控组件
- 非受控组件:ref操作dom,很方便;可以和一些地三方库结合使用
import React,{Component} from 'react'; import {render} from 'react-dom'; class UnControl extends Component{ b = React.createRef(); // 16.3的api React.createRef() handleClick = () =>{ alert(this.a.value); // 写法1 alert(this.b.current.value) // 写法2 } render(){ return (<div> <input type="text" id="username" ref={dom=>this.a=dom}/> <input type="text" id="password" ref={this.b}/> <button onClick={this.handleClick}>点击</button> </div>) } } render(<UnControl></UnControl>,window.root); 复制代码
- 非受控组件:利用e.target和setState来修改状态并控制dom
import React from 'react'; import ReactDOM from 'react-dom'; class Control extends React.Component{ state = { a:'hello', b:'world' } changeHandler = (e)=>{ let val = e.target.name this.setState({ [val]:e.target.value }) } render(){ return ( <div> {this.state.a} {this.state.b} <input type="text" name="a" value={this.state.a} onChange={this.changeHandler}/> <input type="text" name="b" value={this.state.b} onChange={this.changeHandler}/> </div> ) } } ReactDOM.render(<Control></Control>,window.root); 复制代码
react数据传递
- 逐级传递:当组件嵌套的层级不超过3层时,使用这种方式传递数据简单,但是嵌套过深时,会很难管理的问题
//index.js import React, { Component } from 'react'; import ReactDOM from 'react-dom'; import Second1 from './Second1'; import Second from './Second'; class App extends Component { state = { count:0 } handleCountChange = (num)=>{ this.setState({count:num}) } render(){ return( <div> <Second count={this.state.count}></Second> <Second1 count={this.state.count} countChange={this.handleCountChange}></Second1> </div> ) } } ReactDOM.render(<App></App>, window.root); 复制代码
//second.js import React, { Component } from 'react' export default class Second extends Component { render() { let {count} = this.props return ( <div>{count}</div> ) } } 复制代码
//second1.js import React, { Component } from 'react' import Third from './Third'; export default class Second1 extends Component { render() { let {count,countChange} = this.props return ( <Third num={count} numChange={countChange}></Third> ) } } 复制代码
//third.js import React, { Component } from 'react'; export default class Third extends Component { handleClick =()=>{ console.log(this.props.num+1); this.props.numChange(this.props.num+1); } render(){ return ( <span onClick={this.handleClick}>+</span> ) } } 复制代码
- 采用context
import React, { Component } from 'react'; import {Provider} from './context'; import ReactDOM from 'react-dom'; import Second1 from './Second1'; import Second from './Second'; class App extends Component { state = { count:0 } handleCountChange = (num)=>{ this.setState({count:num}) } render(){ return( // 提供一个contex,上面挂载了全局状态 <Provider value={{numChange:this.handleCountChange,num:this.state.count}}> <Second></Second> <Second1></Second1> </Provider> ) } } ReactDOM.render(<App></App>, window.root); 复制代码
// context.js import React from 'react'; let { Provider, Consumer } = React.createContext(); //react提供的API export {Provider,Consumer} 复制代码
// second.js import React, { Component } from 'react'; import {Consumer} from './context'; export default class Second extends Component { render() { return ( <Consumer> {(value)=>{ return <div>{value.num}</div> }} </Consumer> ) } } 复制代码
// second1.js import React, { Component } from 'react' import Third from './Third'; export default class Second1 extends Component { render() { return ( <Third></Third> ) } } 复制代码
//third.js import React, { Component } from 'react'; import {Consumer} from './context'; export default class Third extends Component { render(){ return (<Consumer> {(value)=>{ //固定语法value就是Provider中的value return <span onClick={()=>{value.numChange(value.num + 1)}}>+</span> }} </Consumer>) } } 复制代码
结语:
个人使用一种框架时总有一种想知道为啥这样用的强迫症,不然用框架用的不舒服,不要求从源码上知道其原理,但是必须得从心理上说服自己。
以上就是本文的全部内容,希望本文的内容对大家的学习或者工作能带来一定的帮助,也希望大家多多支持 码农网
猜你喜欢:- 让react用起来更得心应手——(react-router原理简析)
- Tomcat启动流程简析
- Flux模式简析
- fasthttp原理简析
- Android Drawable 简析
- ObjC Runtime简析
本站部分资源来源于网络,本站转载出于传递更多信息之目的,版权归原作者或者来源机构所有,如转载稿涉及版权问题,请联系我们。
Algorithms on Strings, Trees and Sequences
Dan Gusfield / Cambridge University Press / 1997-5-28 / USD 99.99
String algorithms are a traditional area of study in computer science. In recent years their importance has grown dramatically with the huge increase of electronically stored text and of molecular seq......一起来看看 《Algorithms on Strings, Trees and Sequences》 这本书的介绍吧!