Web应用:FireStore缓存-仅读取更改的文档

默认情况下,FireStore SDK disables local persistence of cached data for web clients (但在Android和iOS中默认启用)。如果要启用持久性,请按照 documentation

firebase.firestore().enablePersistence()
  .catch(function(err) {
      if (err.code == 'failed-precondition') {
          // Multiple tabs open, persistence can only be enabled
          // in one tab at a a time.
          // ...
      } else if (err.code == 'unimplemented') {
          // The current browser does not support all of the
          // features required to enable persistence
          // ...
      }
  });
// Subsequent queries will use persistence, if it was enabled successfully

如果文档在本地缓存中是最新的,则不会向您收取读取文档的费用。