[PUT请求在使用GET请求时没有更新JSON，尽管它说成功了？

Question

（仅供参考，我正在使用Jsonbin.io）我有此代码：

// #1
var req2 = new XMLHttpRequest();
req2.onreadystatechange = () => {
  if (req2.readyState == XMLHttpRequest.DONE) {
    alert(req2.responseText);
  } 
};

req2.open("GET", "https://api.jsonbin.io/b/5ed1530b79382f568bcf5662", true);
req2.setRequestHeader("secret-key", "ProbablyNoProblemInTheAPIkey");
req2.send();

// #2

let req = new XMLHttpRequest();

req.onreadystatechange = () => {
  if (req.readyState == XMLHttpRequest.DONE) {
  alert(req.responseText);
  }
};

req.open("PUT", "https://api.jsonbin.io/b/5ed1530b79382f568bcf5662", true);

req.setRequestHeader("secret-key", "ProbablyNoProblemInTheAPIkey");
req.setRequestHeader("Content-Type", "application/json");
req.send('{"Sample": "Hello World"}');

这是我的代码运行的一个示例：

<script language="javascript">
  
document.write(unescape('%3C%21%44%4F%43%54%59%50%45%20%68%74%6D%6C%3E%0A%3C%68%74%6D%6C%3E%0A%20%20%3C%68%65%61%64%3E%0A%20%20%20%20%3C%6D%65%74%61%20%63%68%61%72%73%65%74%3D%22%75%74%66%2D%38%22%3E%0A%20%20%20%20%3C%6D%65%74%61%20%6E%61%6D%65%3D%22%76%69%65%77%70%6F%72%74%22%20%63%6F%6E%74%65%6E%74%3D%22%77%69%64%74%68%3D%64%65%76%69%63%65%2D%77%69%64%74%68%22%3E%0A%20%20%20%20%3C%74%69%74%6C%65%3E%72%65%70%6C%2E%69%74%3C%2F%74%69%74%6C%65%3E%0A%20%20%20%20%3C%6C%69%6E%6B%20%68%72%65%66%3D%22%73%74%79%6C%65%2E%63%73%73%22%20%72%65%6C%3D%22%73%74%79%6C%65%73%68%65%65%74%22%20%74%79%70%65%3D%22%74%65%78%74%2F%63%73%73%22%20%2F%3E%0A%20%20%3C%2F%68%65%61%64%3E%0A%20%20%3C%62%6F%64%79%3E%0A%20%20%20%20%3C%73%63%72%69%70%74%20%3E%0A%0A%0A%0A%0A%2F%2F%20%23%31%0A%76%61%72%20%72%65%71%32%20%3D%20%6E%65%77%20%58%4D%4C%48%74%74%70%52%65%71%75%65%73%74%28%29%3B%0A%72%65%71%32%2E%6F%6E%72%65%61%64%79%73%74%61%74%65%63%68%61%6E%67%65%20%3D%20%28%29%20%3D%3E%20%7B%0A%20%20%69%66%20%28%72%65%71%32%2E%72%65%61%64%79%53%74%61%74%65%20%3D%3D%20%58%4D%4C%48%74%74%70%52%65%71%75%65%73%74%2E%44%4F%4E%45%29%20%7B%0A%20%20%20%20%61%6C%65%72%74%28%72%65%71%32%2E%72%65%73%70%6F%6E%73%65%54%65%78%74%29%3B%0A%20%20%7D%20%0A%7D%3B%0A%0A%72%65%71%32%2E%6F%70%65%6E%28%22%47%45%54%22%2C%20%22%68%74%74%70%73%3A%2F%2F%61%70%69%2E%6A%73%6F%6E%62%69%6E%2E%69%6F%2F%62%2F%35%65%64%31%35%33%30%62%37%39%33%38%32%66%35%36%38%62%63%66%35%36%36%32%22%2C%20%74%72%75%65%29%3B%0A%72%65%71%32%2E%73%65%74%52%65%71%75%65%73%74%48%65%61%64%65%72%28%22%73%65%63%72%65%74%2D%6B%65%79%22%2C%20%22%24%32%62%24%31%30%24%35%50%43%5A%57%2F%2E%35%5A%41%74%62%7A%39%72%72%37%4B%41%73%64%75%35%70%67%58%56%2F%68%79%38%32%50%6F%61%36%45%4C%50%77%49%70%76%6E%54%6A%6D%4E%78%76%61%69%47%22%29%3B%0A%72%65%71%32%2E%73%65%6E%64%28%29%3B%0A%0A%2F%2F%20%23%32%0A%0A%0A%6C%65%74%20%72%65%71%20%3D%20%6E%65%77%20%58%4D%4C%48%74%74%70%52%65%71%75%65%73%74%28%29%3B%0A%0A%72%65%71%2E%6F%6E%72%65%61%64%79%73%74%61%74%65%63%68%61%6E%67%65%20%3D%20%28%29%20%3D%3E%20%7B%0A%20%20%69%66%20%28%72%65%71%2E%72%65%61%64%79%53%74%61%74%65%20%3D%3D%20%58%4D%4C%48%74%74%70%52%65%71%75%65%73%74%2E%44%4F%4E%45%29%20%7B%0A%20%20%61%6C%65%72%74%28%72%65%71%2E%72%65%73%70%6F%6E%73%65%54%65%78%74%29%3B%0A%20%20%7D%0A%7D%3B%0A%0A%72%65%71%2E%6F%70%65%6E%28%22%50%55%54%22%2C%20%22%68%74%74%70%73%3A%2F%2F%61%70%69%2E%6A%73%6F%6E%62%69%6E%2E%69%6F%2F%62%2F%35%65%64%31%35%33%30%62%37%39%33%38%32%66%35%36%38%62%63%66%35%36%36%32%22%2C%20%74%72%75%65%29%3B%0A%0A%72%65%71%2E%73%65%74%52%65%71%75%65%73%74%48%65%61%64%65%72%28%22%73%65%63%72%65%74%2D%6B%65%79%22%2C%20%22%24%32%62%24%31%30%24%35%50%43%5A%57%2F%2E%35%5A%41%74%62%7A%39%72%72%37%4B%41%73%64%75%35%70%67%58%56%2F%68%79%38%32%50%6F%61%36%45%4C%50%77%49%70%76%6E%54%6A%6D%4E%78%76%61%69%47%22%29%3B%0A%72%65%71%2E%73%65%74%52%65%71%75%65%73%74%48%65%61%64%65%72%28%22%43%6F%6E%74%65%6E%74%2D%54%79%70%65%22%2C%20%22%61%70%70%6C%69%63%61%74%69%6F%6E%2F%6A%73%6F%6E%22%29%3B%0A%72%65%71%2E%73%65%6E%64%28%27%7B%22%53%61%6D%70%6C%65%22%3A%20%22%48%65%6C%6C%6F%20%57%6F%72%6C%64%22%7D%27%29%3B%0A%0A%20%20%20%20%3C%2F%73%63%72%69%70%74%3E%0A%20%20%3C%2F%62%6F%64%79%3E%0A%3C%2F%68%74%6D%6C%3E'));
  
</script>

PUT请求应该成功，但是在发出GET请求以访问更新版本时，JSON似乎相同。怎么了？似乎PUT请求已成功完成，因为req.status为200，所以我认为您不应该专注于此。

Answer 1

onreadystatechange异步执行。因此，首先不能保证GET仅在成功完成PUT之后才执行。

其次，在代码中的PUT请求之后，无论如何都已写入GET。

因此，您可以尝试将req2.send();请求的GET放入PUT的“成功”

 req.onreadystatechange = () => {
      if (req.readyState == XMLHttpRequest.DONE) {
          req2.send(); //Try making the GET request once PUT is completed
        //This is gonna execute asynchronously in both the cases 
      } 
    };