如何在单击按钮时将值从ajax传递到控制器？

<button id="myButton">点击按钮</button>

<script>
  document.getElementById("myButton").addEventListener("click", function() {
    var value = "需要传递的值";
    var xhr = new XMLHttpRequest();
    xhr.open("POST", "/controller", true);
    xhr.setRequestHeader("Content-Type", "application/json");
    xhr.onreadystatechange = function() {
      if (xhr.readyState === 4 && xhr.status === 200) {
        var response = JSON.parse(xhr.responseText);
        // 处理后端返回的数据
      }
    };
    xhr.send(JSON.stringify({ value: value }));
  });
</script>

const express = require("express");
const app = express();

app.post("/controller", (req, res) => {
  const value = req.body.value;
  // 对接收到的参数进行处理
  // ...

  // 返回处理结果给前端
  res.json({ result: "处理结果" });
});

app.listen(3000, () => {
  console.log("服务器已启动");
});