给localStorage添加过期时间的功能

 function localset(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}));
}

 function localget(key) {
  var data = localStorage.getItem(key);
  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;
  }
}

export {localset,localget}

//设置localStorage
 localset("user",JSON.stringify(this.users),1800);//设置key为user,值为json字符串，时间为30分钟
//获取localStorage 
 var user=JSON.parse(localget("user"));获取user;