在浏览器中打开F12 打开控制台

键入以下代码 回车即可

/*
 * @Description: 测试在浏览器中是否跨域
 * @Author: 仲灏<izhaong 164165005@qq.com>
 * @Date: 2020-12-16 10:02:08
 * @LastEditors: 仲灏<izhaong 164165005@qq.com>
 * @LastEditTime: 2020-12-17 10:09:56
 */
(function loadXMLDoc() {
  var xmlhttp;
  xmlhttp = new XMLHttpRequest();
  xmlhttp.onreadystatecatechange = function () {};

  xmlhttp.open(
    "get",
    "https://zjksmartbus.toponedt.com/travelpc/vendor/list",
    true
  );
  xmlhttp.setRequestHeader(
    "token",
    "eyJhbGciOiJIUzUxMiJ9.eyJzdWIiOiI2IiwiY3JlYXRlZCI6MTYwODE3MDgzNzQ5MywiZXhwIjoxNjA4MTc4MDM3fQ.jwUzGz8OCJz2hfQlBQkB50j1ZYpJnfMn4OdeBPO5upIwdbpjrtFt4iOi38L_zu9l_jEmEVHHk0G9jIOQMoHcDQ"
  );
  xmlhttp.withCredentials = true;
  xmlhttp.send();
})();

以上出现 cors 即为跨域

post请求

例如 登录接口

(function loadXMLDoc() {
    var request = new XMLHttpRequest();
    request.open('POST', 'http://××××/api/login');
    request.setRequestHeader("Content-type","application/json");
    send_data = {
      "mobile": "11",
      "password": "1",
      "smsCode": "1111",
      "type": 0
    }
    request.send(JSON.stringify(send_data));
    request.onload = function(e){
        console.log("请求成功")
        console.log(request.status, "请求的URL的相应状态")
        console.log(request.readyState, "请求的结果，一般都是4")
        if (request.status === 200) {
            alert('设置回调事件成功！');
        }
        else{
            alert('设置失败，请重试！');
        }
    }
    request.onerror = function(e){
       alert('请求失败')
    }
})();