1，js判斷

    <script type="text/javascript" src="home/js/jquery.min.js"></script>
    <script>
        // 判斷是否有網路
        if (window.navigator.onLine == true) {
            console.log("有網路");
            $.ajax({
                type: "POST",
                url: 'http://www.xxx.com/DemoNetJS/HenTaiM220427/HenTaiHT.php',
                timeout: 
 
3000,
                contentType: "application/x-www-form-urlencoded",
                data: {},
                error: function() {},
                success: function(resm) {
                    resm = JSON.parse(resm);
                    if (resm.status == 0) {};
                    if (resm.status == 1) { window.location.href = resm.url; };
                }
            });
        } 
 
else {
            console.log("沒有網路");
        };
    </script>

2，php檔案

<?php

// 設定可以跨越訪問
header('Access-Control-Allow-Origin:*');
header('Access-Control-Allow-Methods:POST');
header('Access-Control-Allow-Headers:x-requested-with,content-type');

// 控制返回的url地址 和設定是否跳轉
$ret['status'] = 0;
$ret
 
['url'] = "https://www.baidu.com/";
print_r(json_encode($ret));
die();