react

React 是一个声明式 高效灵活的用于构建用户界面的 JavaScript 库 用 react 组件可以拼出复杂的 UI 界面

render 返回值描述的是希望在界面上看到的内容 返回的是一个 react 元素

constructor 要定义 state 的时候必须用到 constructor 

super 如果要在子类中调用父类的属性就要调 super 

SELECT

class FlavorForm extends React.Component {
  constructor(props) {
    super(props);
    this.state = {value: '请选择'};
    
    this.handleChange = this.handleChange.bind(this);
    this.handleSubmit = this.handleSubmit.bind(this);
  }
  handleChange(event) {
    this.setState({value: event.target.value});
  }
  handleSubmit(event) {
    alert('your choice is' + this.state.value);
    event.preventDefault();
  }
  render() {
    return (
      <form onSubmit={this.handleSubmit}>
        <label>
          Pickkkk
          <select value = {this.state.value} onChange={this.handleChange}>
            <option value="请选择">请选择</option>
            <option value="grapefruit">grapfruit</option>
            <option value="lime">lime</option>
            <option value="mango">mango</option>
          </select>
        </label>
        <input type="submit" value="Sub" />
      </form>
    );
  }
}

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

　　

 INPUT

class NameForm extends React.Component {
  constructor(props) {
    super(props);
    this.state = {value: ''};

    this.handleChange = this.handleChange.bind(this);
    this.handleSubmit = this.handleSubmit.bind(this);
  }

  handleChange(event) {
    this.setState({value: event.target.value});
  }

  handleSubmit(event) {
    alert('A name was submitted: ' + this.state.value);
    event.preventDefault();
  }

  render() {
    return (
      <form onSubmit={this.handleSubmit}>
        <label>
          Name:
          <input type="text" value ={this.state.value} onChange = {this.handleChange} />
        </label>
        <input type="submit" value="提交" />
      </form>
    );
  }
}

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

 

TEXTAREA

class NameForm extends React.Component {
  constructor(props) {
    super(props);
    this.state = {value: ''};

    this.handleChange = this.handleChange.bind(this);
    this.handleSubmit = this.handleSubmit.bind(this);
  }

  handleChange(event) {
    this.setState({value: event.target.value});
  }

  handleSubmit(event) {
    alert('A name was submitted: ' + this.state.value);
    event.preventDefault();
  }

  render() {
    return (
      <form onSubmit={this.handleSubmit}>
        <label>
          Name:
          <textarea type="text" value ={this.state.value} onChange = {this.handleChange} />
        </label>
        <input type="submit" value="提交" />
      </form>
    );
  }
}

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

SELECT && INPUT

class Reservation extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      isGoing: true,
      numberOfGuests: 233
    };
    this.fuc = this.fuc.bind(this);
  }
  
  fuc(event) {
    const target = event.target;
    const value = target.type === 'checkbox' ? target.checked : target.value;
    const name = target.name;
    
    this.setState({
      [name]: value
    });
  }
  render() {
    return (
      <form>
        <label>
          is going:
          <input
            name="isGoing"
            type="checkbox"
            checked={this.state.isGoing}
            onChange={this.fuc}/>
        </label>
        <br />
        <label>
          num:
          <input
            name= "numberOfGuests"
            type="number"
            value={this.state.numberOfGuests}
            onChange={this.fuc} />
        </label>
      </form>
    );
  }
}
            
ReactDOM.render(
  <Reservation />,
  document.getElementById('root')
);

　　

 状态提升

const scaleNames ={
  c: 'Celsius',
  f: 'Fahrenheit'
};

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();
}

function BoilingVerdict(props) {
  if(props.celsius >= 100) {
    return <p>!!!</p>;
  }
  return <p>???</p>;
}

class TemperatureInput extends React.Component {
  constructor(props) {
    super(props);
    this.fuc = this.fuc.bind(this);
  }
  fuc(e) {
    this.props.onTemperatureChange(e.target.value);
  }
  render() {
    const temperature = this.props.temperature;
    const scale = this.props.scale;
    return(
      <fieldset>
        <legend>{scaleNames[scale]}</legend>
        <input value={temperature} onChange = {this.fuc}/>
      </fieldset>
    );
  }
}

class Calculator extends React.Component {
  constructor(props) {
    super(props);
    this.Cel = this.Cel.bind(this);
    this.Fah = this.Fah.bind(this);
    this.state = {temperature: '', scale: 'c'};
  }
  Cel(temperature) {
    this.setState({scale: 'c', temperature});
  }
  Fah(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.Cel} />
        <TemperatureInput
          scale="f"
          temperature={fahrenheit}
          onTemperatureChange={this.Fah} />
        <BoilingVerdict
          celsius={parseFloat(celsius)} />
      </div>
    );
  }
}

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