将一个函数作为 props 传递给子组件

index.js

import React from 'react'
import ReactDOM from 'react-dom'

const UserNameInput = ({ getName }) => {
  return (
    <input
      onInput={function (e) {
        getName(e.target.value)
      }}
    />
  )
}
class UserName extends React.Component {
  constructor() {
    super()
    this.state = {
      name: '',
    }
  }
  getName = name => {
    this.setState(() => ({ name }))
  }
  render() {
    return (
      <div>
        <UserNameInput getName={this.getName} />
        <div>{this.state.name}</div>
      </div>
    )
  }
}

ReactDOM.render(<UserName />, document.getElementById('root'))