javascript - 使用Javascript向服务器发送多个请求，直到服务器返回200

Question

我创建了一个 html 页面，用户在等待另一个应用程序重新启动时可以查看该页面。我创建了一个 javascript 脚本，它向应用程序发出多个请求，直到应用程序返回 200。但是，当我尝试打开 html 页面时，浏览器会崩溃。任何人都可以看到我的代码有什么问题吗:

var responseStatus = 404;
var numberOfTries = 0;
var request = new XMLHttpRequest(); 
while(responseStatus != 200){
    console.log("Checking if restart has completed. Attempt number: " + numberOfTries);
    request.open('GET', 'applicationurl', true);
    request.onreadystatechange = function(){
        if (request.readyState === 4){
            console.log("Request Status: " + request.status);
            responseStatus = request.status;
            console.log("Response Status: " + request.status);
            if (request.status != 200) {  
                numberOfTries++;
                console.log("Restart has not yet completed! NumberOfTries: " + numberOfTries);
            }  
        }
    };
    request.send();
}
console.log("Server has successfully restarted");

Answer 1

(在我看来)做到这一点的最佳方法是实际结合 @serge1peshcoff 的两个选项。将调用编写为响应失败时调用自身的函数，并在执行此操作时设置超时。对于大多数目的，您不想在前一个请求之后立即发送另一个请求，您需要等待至少一到五秒以防止向服务器发送垃圾邮件(您也没有给出您期望有多少客户端的指示。什么是对你的浏览器不利对服务器来说可能是可怕的，服务器甚至可能在你的网络应用程序完全启动并返回 200 之前就处理请求)。

此外，setTimeout 是比 setInterval 更好的方法，因为您可以在每次往返时显式重置它。

借用@serge:

function tryRequest(numTries) {
  var responseStatus = 404;
  var request = new XMLHttpRequest(); 
  numTries = numTries || 0;

  console.log("Checking if restart has completed. Attempt number: " + numAttempts);
  request.open('GET', 'applicationurl', true);
  request.onreadystatechange = function(){
      numTries++

      if (request.readyState === 4){
          console.log("Request Status: " + request.status);
          responseStatus = request.status;
          console.log("Response Status: " + request.status);
          if (request.status != 200) {  
              console.log("Restart has not yet completed! NumberOfTries: " + this.attempts);
              setTimeout(tryRequest.bind(null, numTries), 5000); // five seconds
          }  
      }
  };
  request.send();

  console.log("Server has successfully restarted");
}
tryRequest();