在请求调用中设置变量不会更新变量（返回值为 ' '）

Question

试图返回weatherMsg，它是从对天气API 的请求创建的字符串。如控制台日志所示，它正确请求天气。return 是 '' 的初始值。class Weather extends React.Component {    render() {        let request = require('request');        let apiKey = process.env.REACT_APP_WEATHER_API_KEY;        let city = process.env.REACT_APP_WEATHER_CITY;        let url = `http://api.openweathermap.org/data/2.5/weather?id=${city}&units=imperial&appid=${apiKey}`        let weatherMsg = '';        request(url, function (err, response, body) {        if(err){            console.log('error retrieving weather');        } else {            let weather = JSON.parse(body);            console.log(weather);            weatherMsg = "It's {this.state.weather.main.temp} degrees in {this.state.weather.name}.";        }        });        return(            <div>{weatherMsg}</div>        )    }}