当我在没有this.setState(data);一切的情况下使用这个函数时，我在控制台中看到了来自 API 的数据。

当我this.setState(data);在下设置时，console.log(data);我收到如下错误：

Unhandled Rejection (TypeError): this is undefined
componentDidMount/<
src/App.js:42

  39 |       let data = await response.json();
  40 |       
  41 |       console.log(data);
> 42 |       this.setState(data);
     | ^  43 |     });
  44 |   }
  45 | }

代码：

     componentDidMount() {
    if (navigator.geolocation) {
      navigator.geolocation.watchPosition(async function (position) {
        console.log("Latitude is :", position.coords.latitude);
        console.log("Longitude is :", position.coords.longitude);

        var lat = position.coords.latitude;
        var lon = position.coords.longitude;

        const url = `http://api.openweathermap.org/data/2.5/weather?lat=${lat}&lon=${lon}&units=metric&appid=ca148f5dc67f12aafaa56d1878bb6db2`;
        const response = await fetch(url);
        let data = await response.json();
        
        console.log(data);
        this.setState(data);
      });
    }
  }