如何根据嵌套数组中的日期键对对象数组进行排序？

我有如下对象数组：

var dic = [
  {user:'John', notifications:[{created: 'Wed Jan 12 2023 11:58:24 GMT+0200 (Israel Standard Time)'}]},
  {user:'Bob', notifications:[{created: 'Wed Jan 01 2023 11:58:24 GMT+0200 (Israel Standard Time)'}, 
                              {created: 'Wed Feb 01 2023 11:58:24 GMT+0200 (Israel Standard Time)'}]},
  {user:'Ron', notifications:[{created: 'Wed Jan 01 2023 11:58:24 GMT+0200 (Israel Standard Time)'}]},
  {user:'xxx', notifications:[{created: 'Wed Jan 31 2023 11:58:24 GMT+0200 (Israel Standard Time)'}]},
]

我的目标是根据每个对象的notifications数组中的最新日期对原数组进行降序排序，最终结果中Bob应排在首位，因为他的通知里有最新的日期（2月15日），预期结果如下：

var dic = [
  {user:'Bob', notifications:[{created: 'Wed Jan 01 2023 11:58:24 GMT+0200 (Israel Standard Time)'}, 
                              {created: 'Wed Feb 15 2023 11:58:24 GMT+0200 (Israel Standard Time)'}]},
  {user:'xxx', notifications:[{created: 'Wed Jan 31 2023 11:58:24 GMT+0200 (Israel Standard Time)'}]},
  {user:'John', notifications:[{created: 'Wed Jan 12 2023 11:58:24 GMT+0200 (Israel Standard Time)'}]},
  {user:'Ron', notifications:[{created: 'Wed Jan 01 2023 11:58:24 GMT+0200 (Israel Standard Time)'}]},
]

我尝试了如下代码进行排序，但未能成功：

var dic = [
  {user:'John', notifications:[{created: 'Wed Jan 12 2023 11:58:24 GMT+0200 (Israel Standard Time)'}]},
  {user:'Bob', notifications:[{created: 'Wed Jan 01 2023 11:58:24 GMT+0200 (Israel Standard Time)'}, {created: 'Wed Feb 15 2023 11:58:24 GMT+0200 (Israel Standard Time)'}]},
  {user:'Ron', notifications:[{created: 'Wed Jan 01 2023 11:58:24 GMT+0200 (Israel Standard Time)'}]},
  {user:'xxx', notifications:[{created: 'Wed Jan 31 2023 11:58:24 GMT+0200 (Israel Standard Time)'}]},
]

dic.sort((a,b) => {
 //console.log('a', a, 'b', b);
  if(a.notifications.length > 1){
    const test = a.notifications.reduce((a,b) => new Date(a.created).getTime() >= new Date(b.created).getTime() ? a.created : b.created);
    return new Date(test).getTime() >= new Date(b.notifications[0].created).getTime() ? -1 : 1;

  } else{
    return new Date(a.notifications[0].created).getTime() <= new Date(b.notifications[0].created).getTime() ? -1 : 1;

  }

})

console.log(dic)

问题分析 #

原代码存在两个核心问题：

• 仅处理了a的通知数组长度大于1的情况，未对b做同样处理，当b有多个通知时，仅取第一个通知的日期参与比较，导致逻辑错误
• 排序条件判断冗余且不严谨，没有统一获取每个对象的最新通知日期再进行比较

解决方案 #

先封装一个辅助函数，用来获取任意用户对象的最新通知时间戳：

function getLatestNotificationTime(user) {
  return user.notifications.reduce((maxTime, notification) => {
    const currentTime = new Date(notification.created).getTime();
    return currentTime > maxTime ? currentTime : maxTime;
  }, 0);
}

然后利用这个辅助函数进行排序：

var dic = [
  {user:'John', notifications:[{created: 'Wed Jan 12 2023 11:58:24 GMT+0200 (Israel Standard Time)'}]},
  {user:'Bob', notifications:[{created: 'Wed Jan 01 2023 11:58:24 GMT+0200 (Israel Standard Time)'}, {created: 'Wed Feb 15 2023 11:58:24 GMT+0200 (Israel Standard Time)'}]},
  {user:'Ron', notifications:[{created: 'Wed Jan 01 2023 11:58:24 GMT+0200 (Israel Standard Time)'}]},
  {user:'xxx', notifications:[{created: 'Wed Jan 31 2023 11:58:24 GMT+0200 (Israel Standard Time)'}]},
];

dic.sort((a, b) => {
  const aLatest = getLatestNotificationTime(a);
  const bLatest = getLatestNotificationTime(b);
  // 降序排序：时间戳大的对象排在前面
  return bLatest - aLatest;
});

console.log(dic);

该方案通过辅助函数统一获取每个用户的最新通知时间戳，排序时直接用两个时间戳相减，利用数值差实现降序排序，逻辑简洁且严谨，能满足需求。

内容的提问来源于stack exchange，提问作者RoyBarOn