设置localStorage过期时间

/**
     * [以秒做单位, 设置localStorage过期时间]
     */
    var localStorageUtil = {
        set(key, val, expire){
          var exp = expire ? Date.now() + expire*1000 : -1;
          localStorage.setItem(key, JSON.stringify({value: val, expire: exp}));
          console.log('set ok', JSON.stringify({value: val, expire: exp}));
        },
        get(key){
          var data = localStorage.getItem(key);
          console.log(data);

          if(!data) return null;

          var dataObj = JSON.parse(data);

          if(dataObj.expire == -1) return dataObj.value;

          if(Date.now() >= dataObj.expire){
            localStorage.removeItem(key);
            return null;
          }else {
            return dataObj.value;
          }
        }
    }