如何使用ajax将数据发送到node js服务器

var xhr = new XMLHttpRequest();
xhr.open("POST", "/api/data", true);
xhr.setRequestHeader("Content-Type", "application/json");

xhr.onreadystatechange = function() {
  if (xhr.readyState === 4 && xhr.status === 200) {
    // 请求成功处理逻辑
    console.log(xhr.responseText);
  }
};

var data = {
  key1: "value1",
  key2: "value2"
};

xhr.send(JSON.stringify(data));

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

app.use(express.json());

app.post("/api/data", (req, res) => {
  // 处理接收到的数据
  console.log(req.body);

  // 返回响应数据
  res.send("Data received successfully");
});

app.listen(3000, () => {
  console.log("Server started on port 3000");
});