在使用来自firebase的新数据刷新之前清除react状态字段

import React, { Component } from 'react';
import firebase from 'firebase';

class MyComponent extends Component {
  constructor(props) {
    super(props);
    this.state = {
      data: '',
      isLoading: true,
    };
  }

  componentDidMount() {
    // 清除状态字段
    this.setState({
      data: '',
      isLoading: true,
    });

    // 从Firebase获取新数据
    firebase
      .database()
      .ref('path/to/data')
      .once('value')
      .then((snapshot) => {
        const newData = snapshot.val();
        // 更新状态字段
        this.setState({
          data: newData,
          isLoading: false,
        });
      });
  }

  render() {
    const { data, isLoading } = this.state;

    if (isLoading) {
      return <div>Loading...</div>;
    }

    return <div>{data}</div>;
  }
}

export default MyComponent;