bugfix: make suspense and revalidateIfStale work together (vercel#1851)

* bugfix: make suspense and revalidateIfStale work together

* test: add test for revalidateIfStale used with suspense

Author: Simen Owesen-Lein

src/use-swr.ts

@@ -97,13 +97,14 @@ export const useSWRHandler = <Data = any, Error = any>(
     // If it's paused, we skip revalidation.
     if (getConfig().isPaused()) return false
 
-    return suspense
-      ? // Under suspense mode, it will always fetch on render if there is no
-        // stale data so no need to revalidate immediately on mount again.
-        !isUndefined(data)
-      : // If there is no stale data, we need to revalidate on mount;
-        // If `revalidateIfStale` is set to true, we will always revalidate.
-        isUndefined(data) || config.revalidateIfStale
+    // Under suspense mode, it will always fetch on render if there is no
+    // stale data so no need to revalidate immediately on mount again.
+    // If data exists, only revalidate if `revalidateIfStale` is true.
+    if (suspense) return isUndefined(data) ? false : config.revalidateIfStale
+
+    // If there is no stale data, we need to revalidate on mount;
+    // If `revalidateIfStale` is set to true, we will always revalidate.
+    return isUndefined(data) || config.revalidateIfStale
   }
 
   // Resolve the current validating state.

test/use-swr-suspense.test.tsx

@@ -163,6 +163,31 @@ describe('useSWR - suspense', () => {
     await screen.findByText('hello, error') // get error with cache
   })
 
+  it('should not fetch when cached data is present and `revalidateIfStale` is false', async () => {
+    const key = createKey()
+    mutate(key, 'cached')
+
+    let fetchCount = 0
+
+    function Section() {
+      const { data } = useSWR(key, () => createResponse(++fetchCount), {
+        suspense: true,
+        revalidateIfStale: false
+      })
+      return <div>{data}</div>
+    }
+
+    renderWithGlobalCache(
+      <Suspense fallback={<div>fallback</div>}>
+        <Section />
+      </Suspense>
+    )
+
+    screen.getByText('cached')
+    await act(() => sleep(50)) // Wait to confirm fetch is not triggered
+    expect(fetchCount).toBe(0)
+  })
+
   it('should pause when key changes', async () => {
     const renderedResults = []
     const initialKey = createKey()