722_ajax_post请求

2-post.html
<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <style>
      #box {
        width: 200px;
        height: 100px;
        border: solid 1px pink;
      }
    </style>
  </head>
  <body>
    <div id="box"></div>
    <script>
      const box = document.querySelector("#box");
      box.onmouseover = function () {
        //1、创建对象
        const xhr = new XMLHttpRequest();
        //2、初始化
        xhr.open("POST", "http://127.0.0.1:8000/server");
        //设置请求头
        xhr.setRequestHeader(
          "Content-Type",
          "application/x-www-form-urlencoded"
        );
        //3、发送
        //设置请求体的参数
        xhr.send("a=100&b=200");
        //4、事件绑定，处理服务端返回的结果
        xhr.onreadystatechange = function () {
          //判断（服务端返回了所有结果）
          if (xhr.readyState === 4) {
            //判断响应状态码 2##表示成功
            if (xhr.status >= 200 && xhr.status < 300) {
              box.innerHTML = xhr.response;
            } else {
            }
          }
        };
      };
    </script>
  </body>
</html>