原生js如何跨域

<script>
function handleResponse(response) {
    console.log('跨域数据：', response);
}
</script>
<script src="http://example.com/data?callback=handleResponse"></script>

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

app.use((req, res, next) => {
    res.header('Access-Control-Allow-Origin', '*'); // 允许所有域
    res.header('Access-Control-Allow-Headers', 'Origin, X-Requested-With, Content-Type, Accept');
    next();
});

app.get('/data', (req, res) => {
    res.json({ message: '这是跨域数据' });
});

app.listen(3000, () => {
    console.log('服务器运行在 http://localhost:3000');
});

const express = require('express');
const { createProxyMiddleware } = require('http-proxy-middleware');

const app = express();

app.use('/api', createProxyMiddleware({
    target: 'http://example.com',
    changeOrigin: true,
    pathRewrite: {
        '^/api': ''
    }
}));

app.listen(3000, () => {
    console.log('代理服务器运行在 http://localhost:3000');
});

const socket = new WebSocket('ws://example.com/socketserver');

socket.onopen = function() {
    console.log('连接成功');
    socket.send('Hello Server!');
};

socket.onmessage = function(event) {
    console.log('收到消息：', event.data);
};

// 在两个不同子域名的页面中设置相同的 document.domain
document.domain = 'example.com';