1this.forceUpdate()
2

1import React, {Component} from 'react'
2import ReactDOM from 'react-dom'
3

1render () {
2  this.state.username
3  const { username } = this.state
4  ···
5}
6 
7 
8

1class Hello extends Component {
2  ...
3}
4

1import React, {
2  Component,
3  Fragment
4} from 'react'
5
6class Info extends Component {
7  render () {
8    const { avatar, username } = this.props
9
10    return (
11      <Fragment>
12        <UserAvatar src={avatar} />
13        <UserProfile username={username} />
14      </Fragment>
15    )
16  }
17}
18

1const el = document.body
2ReactDOM.render(<Hello name='John' />, el)
3

1constructor(props) {
2  super(props)
3  this.state = { username: undefined }
4}
5