• React-状态提升


    通常,多个组件需要反映相同的变化数据,这时建议将共享状态提升到最近的共同父组件中去。
    
    <!DOCTYPE html>
    <html>
    
    <head>
        <meta charset="UTF-8" />
        <title>T-React</title>
        <script src="https://cdn.staticfile.org/react/16.4.0/umd/react.development.js"></script>
        <script src="https://cdn.staticfile.org/react-dom/16.4.0/umd/react-dom.development.js"></script>
        <!-- 生产环境中不建议使用 -->
        <script src="https://cdn.staticfile.org/babel-standalone/6.26.0/babel.min.js"></script>
    </head>
    
    <body>
    
    <div id="root"></div>
    <script type="text/babel">
    
    function BoilingVerdict(props) {
      if (props.celsius >= 100) {
        return <p>The water would boil.</p>;
      }
      return <p>The water would not boil.</p>;
    }
    
    function toCelsius(fahrenheit) {
      return (fahrenheit - 32) * 5 / 9;
    }
    
    function toFahrenheit(celsius) {
      return (celsius * 9 / 5) + 32;
    }
    
    function tryConvert(temperature, convert) {
      const input = parseFloat(temperature);
      if (Number.isNaN(input)) {
        return '';
      }
      const output = convert(input);
      const rounded = Math.round(output * 1000) / 1000;
      return rounded.toString();
    }
    
    const scaleNames = {
      c: 'Celsius',
      f: 'Fahrenheit'
    };
    
    class TemperatureInput extends React.Component {
      constructor(props) {
        super(props);
        this.handleChange = this.handleChange.bind(this);
      }
    
      handleChange(e) {
        this.props.onTemperatureChange(e.target.value);
      }
    
      render() {
        const temperature = this.props.temperature;
        const scale = this.props.scale;
        return (
          <fieldset>
            <legend>Enter temperature in {scaleNames[scale]}:</legend>
            <input value={temperature}
                   onChange={this.handleChange} />
          </fieldset>
        );
      }
    }
    
    class Calculator extends React.Component {
      constructor(props) {
        super(props);
        this.handleCelsiusChange = this.handleCelsiusChange.bind(this);
        this.handleFahrenheitChange = this.handleFahrenheitChange.bind(this);
        this.state = {temperature: '', scale: 'c'};
      }
    
      handleCelsiusChange(temperature) {
        this.setState({scale: 'c', temperature});
      }
    
      handleFahrenheitChange(temperature) {
        this.setState({scale: 'f', temperature});
      }
    
      render() {
        const scale = this.state.scale;
        const temperature = this.state.temperature;
        const celsius = scale === 'f' ? tryConvert(temperature, toCelsius) : temperature;
        const fahrenheit = scale === 'c' ? tryConvert(temperature, toFahrenheit) : temperature;
    
        return (
          <div>
            <TemperatureInput
              scale="c"
              temperature={celsius}
              onTemperatureChange={this.handleCelsiusChange} />
    
            <TemperatureInput
              scale="f"
              temperature={fahrenheit}
              onTemperatureChange={this.handleFahrenheitChange} />
    
            <BoilingVerdict
              celsius={parseFloat(celsius)} />
          </div>
        );
      }
    }
        ReactDOM.render(
            <Calculator />, //JSX格式
            document.getElementById("root")
        );
    
    </script>
    </body>
    
    </html>
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  • 原文地址:https://www.cnblogs.com/csnd/p/12061874.html
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