您可以使用 FieldValue.serverTimestamp()

serverTimestamp():FieldValue返回与set()一起使用的哨兵或update()在写入的数据中包含服务器生成的时间戳.

serverTimestamp(): FieldValue Returns a sentinel used with set() or update() to include a server-generated timestamp in the written data.

'createdOn':FieldValue.serverTimestamp()

参考文献

• ServerTimestamp