1. 每次请求都会带上 cookie 到服务端, 有些跨域的请求, 服务端不允许携带 cookie 的话就会报错
2. cookie 中的数据特别大的话, 会导致请求速度特别慢

(function () {
  var cookieMgr = {};

  // 获取 cookie
  cookieMgr.get = function (key) {
    var cookies = document.cookie.split("; ");
    var item;
    for (var i = 0; i < cookies.length; i++) {
      item = cookies[i].split("=");
      if (item[0] === key) {
        return item[1];
      }
    }
  };

  // 设置cookie
  cookieMgr.set = function (key, val, expired) {
    document.cookie = String(key) + "=" + val + ";max-age=" + expired;
    return this;
  };

  // 删除cookie
  cookieMgr.delete = function (key) {
    return this.set(key, "", -1);
  };

  // 判断是否有某个值
  cookieMgr.has = function (key) {
    return Boolean(this.get(key));
  };

  // 能获取到就没过期, 过期了就无法获取到
  cookieMgr.isExpired = function (key) {
    return cookieMgr.has(key);
  };

  Object.freeze && Object.freeze(cookieMgr);

  return cookieMgr;
})();