将API参数存入常量后Node.js应用崩溃，请求排查解决

问题 #

为何将API密钥、位置等参数存入常量后，我的Node.js应用会崩溃？若注释第一个拼接的const url，直接使用写死参数的URL则运行正常。

代码示例 #

app.get('/', function(req, res) {
    const query = "London";
    const apiKey = "c3fd0e578a1e8ead729deb6f25";
    const unit = "metric";

    const url = "https://api.openweathermap.org/data/2.5/weather?q=" + query + "&appid=" + apiKey + "&units=" + unit;

    const url = "https://api.openweathermap.org/data/2.5/weather?q=London&appid=c3fd0e578a1e8ead729deb6f25d&units=metric"
    
    https.get(url, function(response) {
        console.log(response.statusCode);

        response.on("data", function(data) {
            const weatherData = JSON.parse(data);
            const temp = weatherData.main.temp;
            const weatherDescription = weatherData.weather[0].description;
            
            const icon = weatherData.weather[0].icon;
            const iconURL = "http://openweathermap.org/img/wn/" + icon + "@2x.png";
            
            res.set("Content-Type", "text/html");
            res.write("<h1>The temperature in London is " + temp + "C</h1>");
            res.write("<p>The weather is currencly " + weatherDescription + "</p>");
            res.write("<img src=" + iconURL + ">");
            res.send();
        });
});

终端报错信息 #

/Users/Desktop/code/Web Dev. Bootcamp/WeatherProject/app.js:22
            const temp = weatherData.main.temp;
                                          ^

TypeError: Cannot read properties of undefined (reading 'temp')
    at IncomingMessage.<anonymous> (/Users/Desktop/code/Web Dev. Bootcamp/WeatherProject/app.js:22:43)
    at IncomingMessage.emit (node:events:513:28)
    at Readable.read (node:internal/streams/readable:539:10)
    at flow (node:internal/streams/readable:1023:34)
    at resume_ (node:internal/streams/readable:1004:3)
    at process.processTicksAndRejections (node:internal/process/task_queues:82:21)

Node.js v18.13.0
[nodemon] app crashed - waiting for file changes before starting...

报错指向const temp行，注释该行后会报错下一行。

解决方案 #

问题根源有两个：

• API密钥不匹配
  拼接URL时使用的apiKey值是c3fd0e578a1e8ead729deb6f25，而写死的URL里用的是c3fd0e578a1e8ead729deb6f25d（末尾多了一个d）。密钥错误会导致OpenWeatherMap API返回错误信息而非正常天气数据，此时weatherData.main为undefined，读取temp自然会触发类型错误。

• 重复声明常量
  连续两次用const声明url，这违反了JavaScript中const变量不可重复声明的规则。虽然当前代码可能因后面的声明覆盖了前面的（严格模式下会直接抛出语法错误），但这是不规范的写法，必须修正。

具体修复步骤 #

1. 修正API密钥
   将apiKey的值改为写死URL中的有效密钥：

   const apiKey = "c3fd0e578a1e8ead729deb6f25d";
   

2. 删除重复的url声明
   只保留拼接生成的url（这种方式更利于后续参数修改）：

   // 仅保留这一行
   const url = "https://api.openweathermap.org/data/2.5/weather?q=" + query + "&appid=" + apiKey + "&units=" + unit;
   

3. 添加错误处理（可选但推荐）
   为了避免API返回错误时应用崩溃，可以在解析数据后先判断请求状态：

   response.on("data", function(data) {
       const weatherData = JSON.parse(data);
       // 检查API返回的状态码
       if (weatherData.cod !== 200) {
           res.send("<h1>获取天气失败：" + weatherData.message + "</h1>");
           return;
       }
       // 后续正常处理逻辑
       const temp = weatherData.main.temp;
       const weatherDescription = weatherData.weather[0].description;
       // ... 其余代码
   });
   

内容的提问来源于stack exchange，提问作者Eduard