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1610020510.js

class App extends React.Component {
  constructor() {
    super()
    this.state = {
      m: 0
    }
  }

  static getDerivedStateFromProps(nextProps, prevState) {
    console.log("getDerived", nextProps, prevState);
    if (nextProps.n !== prevState.m) {
      // 这里 return 的对象相当于 setState 了
      return {
        m: nextProps.n
      }
    }

    return null
  }
  
  render() {
    return (
      <div>{m}</div>     )
  }
}