js：json请求和jsonp请求

$ pnpm i express

// server.js
const express = require("express");
const app = express();
// 返回json数据
app.get("/api/json", (request, response) => {
  response.json({ msg: "ok" });
});
const port = process.env.PORT || 5000;
app.listen(port, () => {
  console.log(`Server runing on http://127.0.0.1:${port}`);
});

$ node server.js
Server runing on http://127.0.0.1:5000

$ pnpm i http-server
# 启动静态服务器
$ npx http-server -p 5500 -c-1

前端访问地址：http://127.0.0.1:5500/index.html
接口地址：http://127.0.0.1:5000/api/json

// script.js
fetch("http://127.0.0.1:5000/api/json")
      .then(function (response) {
        return response.json();
      })
      .then(function (data) {
        console.log(data);
      });

Access to fetch at 'http://127.0.0.1:5000/api/json' 
from origin 'http://127.0.0.1:5500' has been blocked by CORS policy: 
No 'Access-Control-Allow-Origin' header is present on the requested resource. 
If an opaque response serves your needs, 
set the request's mode to 'no-cors' to fetch the resource with CORS disabled.

$ pnpm i cors

// server.js
const express = require("express");
var cors = require('cors')
const app = express();
// 开启跨域
app.use(cors())
// 返回json数据
app.get("/api/json", (request, response) => {
  response.json({ msg: "ok" });
});
const port = process.env.PORT || 5000;
app.listen(port, () => {
  console.log(`Server runing on http://127.0.0.1:${port}`);
});

// server.js
const express = require("express");
// var cors = require('cors')
const app = express();
// 开启跨域
// app.use(cors())
// 返回json数据
app.get("/api/json", (request, response) => {
  response.json({ msg: "ok" });
});
// 返回jsonp数据
app.get("/api/jsonp", (request, response) => {
    response.jsonp({ msg: "ok" });
  });
const port = process.env.PORT || 5000;
app.listen(port, () => {
  console.log(`Server runing on http://127.0.0.1:${port}`);
});

// 动态导入script
function importScript(src) {
  var hm = document.createElement("script");
  hm.src = src;
  var s = document.getElementsByTagName("script")[0];
  s.parentNode.insertBefore(hm, s);
}
// 全局的响应处理函数
function handleResponse(res) {
  console.log(res);
}
(function () {
  sendJsonpBtn.addEventListener("click", function () {
    importScript("http://127.0.0.1:5000/api/jsonp?callback=handleResponse");
    // jsonp的响应
    // /**/ typeof handleResponse === 'function' && handleResponse({"msg":"ok"});
  });
})();