TanStack Query provides three different network modes to distinguish how Queries and Mutations should behave if you have no network connection. This mode can be set for each Query / Mutation individually, or globally via the query / mutation defaults.
Since TanStack Query is most often used for data fetching in combination with data fetching libraries, the default network mode is online.
In this mode, Queries and Mutations will not fire unless you have network connection. This is the default mode. If a fetch is initiated for a query, it will always stay in the state (loading, error, success) it is in if the fetch cannot be made because there is no network connection. However, a fetchStatus is exposed additionally. This can be either:
The flags isFetching and isPaused are derived from this state and exposed for convenience.
Keep in mind that it might not be enough to check for loading state to show a loading spinner. Queries can be in state: 'loading', but fetchStatus: 'paused' if they are mounting for the first time, and you have no network connection.
If a query runs because you are online, but you go offline while the fetch is still happening, TanStack Query will also pause the retry mechanism. Paused queries will then continue to run once you re-gain network connection. This is independent of refetchOnReconnect (which also defaults to true in this mode), because it is not a refetch, but rather a continue. If the query has been cancelled in the meantime, it will not continue.
In this mode, TanStack Query will always fetch and ignore the online / offline state. This is likely the mode you want to choose if you use TanStack Query in an environment where you don't need an active network connection for your Queries to work - e.g. if you just read from AsyncStorage, or if you just want to return Promise.resolve(5) from your queryFn.
This mode is the middle ground between the first two options, where TanStack Query will run the queryFn once, but then pause retries. This is very handy if you have a serviceWorker that intercepts a request for caching like in an offline-first PWA, or if you use HTTP caching via the Cache-Control header.
In those situations, the first fetch might succeed because it comes from an offline storage / cache. However, if there is a cache miss, the network request will go out and fail, in which case this mode behaves like an online query - pausing retries.
The TanStack Query Devtools will show Queries in a paused state if they would be fetching, but there is no network connection. There is also a toggle button to Mock offline behavior. Please note that this button will not actually mess with your network connection (you can do that in the browser devtools), but it will set the OnlineManager in an offline state.