Ajax解决跨域之设置CORS响应头实现跨域案例详解

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>CORS</title>
    <style>
        #result {
            width: 200px;
            height: 100px;
            border: solid 1px #90b;
        }
    </style>
</head>

<body>
    <button>发送请求</button>
    <div id="result"></div>
    <script>
        const btn = document.querySelector('button');

        btn.onclick = function () {
            //1. 创建对象
            const x = new XMLHttpRequest();
            //2. 初始化设置
            x.open("GET", "http://127.0.0.1:8080/cors-server");
            //3. 发送
            x.send();
            //4. 绑定事件
            x.onreadystatechange = function () {
                if (x.readyState === 4) {
                    if (x.status >= 200 && x.status < 300) {
                        document.getElementById('result').innerText = x.response;
                    }
                }
            }
        }
    </script>
</body>

</html>

//1. 引入express
const express = require('express');

//2. 创建应用对象
const app = express();
 
//3. 创建路由规则
// request 是对请求报文的封装
// response 是对响应报文的封装

app.all('/cors-server', (request, response)=>{
    //设置响应头
    response.setHeader("Access-Control-Allow-Origin", "*");// 允许请求所有跨域 * 
    // response.setHeader("Access-Control-Allow-Origin", "http://127.0.0.1:5500"); // 允许指定请求跨域
    // response.setHeader("Access-Control-Allow-Headers", '*');// 允许自定义请求头标签
    // response.setHeader("Access-Control-Allow-Method", '*');// 允许所有的请求跨域 *
    // response.setHeader("Access-Control-Allow-Method", 'get');// 允许get请求跨域

    response.send('hello CORS');
});


//4. 监听端口启动服务
app.listen(8080, () => {
    console.log("服务已经启动, 8080 端口监听中....");
});