Babel 转译器 这是react自带的一个编译器
props和states一个是组件外部的，一个是组件内部的
jsx代表objects.
Hello.js
import React from ‘react‘; export default ({ name }) => <h1>Hello {name}!</h1>;
index.html
<div id="root"></div>
index.js
import React, { Component } from ‘react‘;
import { render } from ‘react-dom‘;
import Hello from ‘./Hello‘;
import ‘./style.css‘;
import Name from ‘./Name‘;
class App extends Component {
constructor() {
super();
this.state = {
name: ‘React1‘,
insertName: ‘xss‘,
hasNameFlag :true
};
}
changeName = () => {
this.setState({
insertName: ‘yys‘,
})
}
deleteName = () =>{
this.setState({
hasNameFlag :false
})
}
render() {
const { insertName,hasNameFlag} = this.state;
const a = (
<h1 className={"greeting"} title="yys">
Hello, world!
</h1>
);
let name = null;
if(hasNameFlag){
name = <Name name={insertName} />;
}
return (
<div>
<Hello name={this.state.name} />
{name}
<button onClick={this.changeName}>改名</button>
<button onClick={this.deleteName}>删除</button>
<p>
Start editing to see some magic happen :)
</p>
</div>
);
}
}
render(<App />, document.getElementById(‘root‘));
Name.js
import React, { Component } from ‘react‘;
class Name extends Component {
constructor(props) {
super(props);
this.state = {
name: props.name
};
}
componentWillReceiveProps(nextProps){
if(nextProps.name === this.props.name) return;
this.setState({
name:nextProps.name
})
}
componentDidUpdate(){
console.log("componentDidUpdate");
}
componentWillUnmount(){
console.log("componentWillUnmount");
}
render() {
const { name } = this.state;
return <h2>{name}</h2>
}
}
export default Name;
constructor 1 只执行一次
compomentwillMount 1 dom放进去之前，也是只执行一次
componentDidMount 1 dom放进去之后，也是只执行一次
componentwillReceIveProps 有改变就执行，修改states的时候用到
componentwillupDate dom更新之前
componentDidupDate dom更新之后
componentWillUnmount dom组件被移除之前被调用，可以用于做一些清理工作