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React 性能优化

Profiler API

Profiler 衡量React应用程序渲染的频率以及渲染的“成本”是多少。

其目的是帮助识别应用程序中速度较慢的部分，并可能从诸如memoization 之类的优化中受益。

⚠️ 分析会增加一些额外的开销, 因此在生产版本中将其禁用。

https://reactjs.org/docs/profiler.html

render(
  <App>
    <Profiler id="Navigation" onRender={callback}>
      <Navigation {...props} />
    </Profiler>
    <Main {...props} />
  </App>
);

render(
  <App>
    <Profiler id="Navigation" onRender={callback}>
      <Navigation {...props} />
    </Profiler>
    <Profiler id="Main" onRender={callback}>
      <Main {...props} />
    </Profiler>
  </App>
);

render(
  <App>
    <Profiler id="Panel" onRender={callback}>
      <Panel {...props}>
        <Profiler id="Content" onRender={callback}>
          <Content {...props} />
        </Profiler>
        <Profiler id="PreviewPane" onRender={callback}>
          <PreviewPane {...props} />
        </Profiler>
      </Panel>
    </Profiler>
  </App>
);

function onRenderCallback(
  id, // the "id" prop of the Profiler tree that has just committed
  phase, // either "mount" (if the tree just mounted) or "update" (if it re-rendered)
  actualDuration, // time spent rendering the committed update
  baseDuration, // estimated time to render the entire subtree without memoization
  startTime, // when React began rendering this update
  commitTime, // when React committed this update
  interactions // the Set of interactions belonging to this update
) {
  // Aggregate or log render timings...
}

React Profiler

https://reactjs.org/blog/2018/09/10/introducing-the-react-profiler.html

https://www.youtube.com/watch?v=00RoZflFE34

Performance Tools

https://reactjs.org/docs/perf.html

Optimizing Performance

https://reactjs.org/docs/optimizing-performance.html#use-the-production-build

Webpack v4+ will minify your code by default in production mode.

const TerserPlugin = require('terser-webpack-plugin');

module.exports = {
  mode: 'production',
  optimization: {
    minimizer: [new TerserPlugin({ /* additional options here */ })],
  },
};

shouldComponentUpdate

SCU

// React.Component

class CounterButton extends React.Component {
  constructor(props) {
    super(props);
    this.state = {count: 1};
  }

  shouldComponentUpdate(nextProps, nextState) {
    if (this.props.color !== nextProps.color) {
      return true;
    }
    if (this.state.count !== nextState.count) {
      return true;
    }
    return false;
  }

  render() {
    return (
      <button
        color={this.props.color}
        onClick={() => this.setState(state => ({count: state.count + 1}))}>
        Count: {this.state.count}
      </button>
    );
  }
}

just inherit from React.PureComponent

// React.PureComponent

class CounterButton extends React.PureComponent {
  constructor(props) {
    super(props);
    this.state = {count: 1};
  }

  render() {
    return (
      <button
        color={this.props.color}
        onClick={() => this.setState(state => ({count: state.count + 1}))}>
        Count: {this.state.count}
      </button>
    );
  }
}

Most of the time, you can use React.PureComponent instead of writing your own shouldComponentUpdate.
它只会进行浅层比较，因此，如果道具或状态可能以浅层比较可能会丢失的方式被使用，则您将无法使用它。

update bug

class ListOfWords extends React.PureComponent {
  render() {
    return <div>{this.props.words.join(',')}</div>;
  }
}

class WordAdder extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      words: ['marklar']
    };
    this.handleClick = this.handleClick.bind(this);
    this.updateColorMap = this.updateColorMap.bind(this);
  }

  handleClick() {
    // This section is bad style and causes a bug
    const words = this.state.words;
    words.push('marklar');
    this.setState({words: words});
  }

   updateColorMap(colormap) {
    colormap.right = 'blue';
   }

  render() {
    return (
      <div>
        <button onClick={this.handleClick} />
        <ListOfWords words={this.state.words} />
       <button onClick={this. updateColorMap} />
      </div>
    );
  }
}

solutions

1. array update

handleClick() {
  this.setState(state => ({
    words: state.words.concat(['marklar'])
  }));
}

handleClick() {
  this.setState(state => ({
    words: [...state.words, 'marklar'],
  }));
};

2. object update

function updateColorMap(colormap) {
  return Object.assign({}, colormap, {right: 'blue'});
}

function updateColorMap(colormap) {
  return {...colormap, right: 'blue'};
}

refs

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