访问下拉列表的DOM元素

Question

我有一个下拉列表，我使用它来允许用户建立到后端的查询参数。

然后，用户将单击一个按钮，我将访问用户在下拉列表中设置的值，以调用后端endpoint。

<div className="wrappers">

<div className="timeFrameLabel label">Time Frame: </div>  
<select ref="timeFrame" className="timeFrameDropdown dropdown">
   <option>1m</option>
   <option>5m</option>
   <option>15m</option>
   <option>30m</option>
   <option>1h</option>
   <option>4h</option>
   <option>1d</option>
</select> 
</div>

<Button className="goButton" onClick={this.getBacktestData}>
                Get Data
</Button>

getBacktestData = async() => {
        const { 
            symbol,
            binSize,
            startTime,
            endTime,
        } = this.state;
        var quantity = document.querySelector(".quantityDropdown select")[document.querySelector(".quantityDropdown select").selectedIndex].innerHTML;

        console.log(this.refs.asset.select)
        console.log(this.refs.timeFrame)
        console.log(this.refs.amount)


        return await fetch("http://localhost:3001/backtest/getdata", {
            method: 'POST',
            body: JSON.stringify({symbol:symbol, binSize: binSize, startTime:startTime, endTime:endTime}), // data can be `string` or {object}!
            headers:{
                'Content-Type': 'application/json'
            }
        })
        .then(res => res.json())
        .then(response => console.log(response))
        .catch(error => console.error('Error:', error))
    }

任何帮助或提示都是非常欢迎的。

Answer 1

下面是访问select值的惯用方法，而不必使用DOM。

class MyComponent extends React.Component {
  constructor(props) {
    super(props);
    this.state = { selected: null };
  }

  handleChange = e => {
    this.setState({ selected: e.target.value });
  };

  getBacktestData = async () => {
    const { selected } = this.state;
    // Do something with the selected value
  };

  render() {
    return (
      <React.Fragment>
        Selected: {this.state.selected}
        <select value={this.state.selected} onChange={this.handleChange}>
          <option value="1m">1m</option>
          <option value="5m">5m</option>
          <option value="15m">15m</option>
          <option value="30m">30m</option>
          <option value="1h">1h</option>
          <option value="4h">4h</option>
          <option vlaue="1d">1d</option>
        </select>
      </React.Fragment>
    );
  }
}