javascript - 在函数外部使用变量

Question

我首先要说的是，我真的很想学习 Node，但遇到了一些困难。我正在构建一个 super 简单的天气应用程序，它调用 API，然后我想返回数据。

但我不确定为什么它不会将此数据返回到控制台？

var request = require('request');

request('https://api.forecast.io/forecast/{API KEY}/42.47994,-83.13040', function (error, response, body) {
    if (!error && response.statusCode == 200) {
      //var info = JSON.parse(body);
      var jsonObject = JSON.parse(body);
      var summary = jsonObject.currently.summary;
      var temp = jsonObject.currently.temperature;
      var realFeel = jsonObject.currently.apparentTemperature;
      var summary2 = jsonObject.hourly.summary;
      var max = jsonObject.daily.data[0].temperatureMax;
      var min = jsonObject.daily.data[0].temperatureMin;
    }
})
console.log('Todays forecast ' + summary2 + ' With a current Tempature of ' + temp + '. But feels like ' +realFeel + ' With a high of '+max+' and a low of '+min);

Answer 1

Node 是一个异步服务器。当你执行一个将要阻塞的请求时， Node 引擎继续执行下面的代码。您向请求模块传递了一个回调，但您的 console.log 在请求发出之后以及结果返回之前立即执行。

您想要做的是将代码放在回调函数内使用数据的位置。

var request = require('request');

request('https://api.forecast.io/forecast/{API KEY}/42.47994,-83.13040', function (error, response, body) {
    if (!error && response.statusCode == 200) {
      //var info = JSON.parse(body);
      var jsonObject = JSON.parse(body);
      var summary = jsonObject.currently.summary;
      var temp = jsonObject.currently.temperature;
      var realFeel = jsonObject.currently.apparentTemperature;
      var summary2 = jsonObject.hourly.summary;
      var max = jsonObject.daily.data[0].temperatureMax;
      var min = jsonObject.daily.data[0].temperatureMin;
      console.log('Todays forecast ' + summary2 + ' With a current Tempature of ' + temp + '. But feels like ' +realFeel + ' With a high of '+max+' and a low of '+min);
    }
})

您也不应该忽略错误。

var request = require('request');

request('https://api.forecast.io/forecast/{API KEY}/42.47994,-83.13040', function (error, response, body) {
    if (error) throw error;
    if (response.statusCode != 200) return console.log('Invalid status code: '+response.statusCode)                     
    var jsonObject = JSON.parse(body);
    var summary = jsonObject.currently.summary;
    var temp = jsonObject.currently.temperature;
    var realFeel = jsonObject.currently.apparentTemperature;
    var summary2 = jsonObject.hourly.summary;
    var max = jsonObject.daily.data[0].temperatureMax;
    var min = jsonObject.daily.data[0].temperatureMin;
    console.log('Todays forecast ' + summary2 + ' With a current Tempature of ' + temp + '. But feels like ' +realFeel + ' With a high of '+max+' and a low of '+min);
});