Web / TanStack Interview Questions
What is the difference between staleTime and gcTime in TanStack Query?
These are the most commonly confused options — they govern completely different lifecycle phases.
| Option | Controls | Default |
|---|---|---|
| staleTime | How long cached data is 'fresh' — no background refetch while fresh | 0 ms (immediately stale) |
| gcTime | How long an unused cache entry (no subscribers) stays in memory before GC | 5 minutes |
const { data } = useQuery({
queryKey: ["config"],
queryFn: fetchConfig,
staleTime: 1000*60*10, // fresh 10 min — no background refetch
gcTime: 1000*60*30, // kept 30 min after last subscriber leaves
})
// t=0: fetched. FRESH.
// t=8min: remount. Still FRESH — cache hit, no network call.
// t=11min: remount. STALE — serves cache, refetches in background.
// t=35min: unmounted 30 min — cache REMOVED by GC.Tip: staleTime:Infinity means data never goes stale automatically — only explicit invalidateQueries() refreshes it. Ideal for app config or country lists.
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