我是 javascript fetch api 的新手。我在本地主机端口 3000 中启动并运行了一个服务器，我想向其发布请求。 这是服务器代码。

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


app.use(express.json());


let data = "";
fs.readFile("data.json",(err,da) => {
  data = JSON.parse(da);
});

app.post("/add/user/",(req,res) => {
  const newData = {
    user: data.length + 1,name: req.body.name,pass: req.body.pass,};

  data.push(newData);
  res.send(data);
  data_to_write = JSON.stringify(data,null,2);

  fs.writeFile("data.json",data_to_write,(err) => {
    console.log("file has been updated");
  });
});

const port = process.env.PORT || 3000;

app.listen(port,() => {
  console.log(`the app is running now in the port ${port} `);
});

但是当我尝试使用 fetch 函数发送 post 请求时

let name = "Saroj";
let pass = "dhfjhdjhfjkd";


let data = { 
  name : name,pass : pass,}

const options = {
  method : "POST",Headers : {
    "Content-Type":"application/json"
  },body : JSON.stringify(data)
}


fetch("http://localhost:3000/add/user",options);

我明白了：

Uncaught (in promise) TypeError: Failed to fetch

和

POST http://localhost:3000/add/user net::ERR_FAILED

但是当我尝试使用邮递员应用发帖时，它工作正常，我该如何解决这个问题。谢谢?