From 601fe3e34d9537f660043daec343d9dabff2c9b2 Mon Sep 17 00:00:00 2001
From: huozhi <gilesliu12@gmail.com>
Date: Thu, 7 May 2020 11:23:02 +0800
Subject: [PATCH] throw promise when key is falsy in suspense

---
 src/use-swr.ts        | 13 +++++++----
 test/use-swr.test.tsx | 53 +++++++++++++++++++++++++++----------------
 2 files changed, 42 insertions(+), 24 deletions(-)

diff --git a/src/use-swr.ts b/src/use-swr.ts
index c744a5ecf..fd57d4a10 100644
--- a/src/use-swr.ts
+++ b/src/use-swr.ts
@@ -372,7 +372,7 @@ function useSWR<Data = any, Error = any>(
 
     // update the state if the key changed (not the inital render) or cache updated
     if (
-      (keyRef.current !== key && (!keyRef.current && !key)) ||
+      keyRef.current !== key ||
       !config.compare(currentHookData, latestKeyedData)
     ) {
       dispatch({ data: latestKeyedData })
@@ -543,10 +543,15 @@ function useSWR<Data = any, Error = any>(
       typeof latestError === 'undefined'
     ) {
       // need to start the request if it hasn't
+
       if (!CONCURRENT_PROMISES[key]) {
-        // trigger revalidate immediately
-        // to get the promise
-        revalidate()
+        if (key) {
+          // trigger revalidate immediately
+          // to get the promise
+          revalidate()
+        } else {
+          throw Promise.reject()
+        }
       }
 
       if (
diff --git a/test/use-swr.test.tsx b/test/use-swr.test.tsx
index cc09825af..e7e28ef01 100644
--- a/test/use-swr.test.tsx
+++ b/test/use-swr.test.tsx
@@ -1270,36 +1270,49 @@ describe('useSWR - suspense', () => {
 
   // hold render when suspense
   it('should pause when key is falsy', async () => {
-    const renderedResults = []
-
-    function Section() {
-      const [key, setKey] = useState(null)
+    function SectionContent({ swrKey, onClick }) {
       const { data } = useSWR(
-        key,
-        k => new Promise(res => setTimeout(() => res(k), 50)),
+        () => (swrKey % 2 === 0 ? null : swrKey),
+        k => new Promise(res => setTimeout(() => res(k), 30)),
         {
           suspense: true
         }
       )
 
-      useEffect(() => {
-        setKey('suspense-9')
-      }, [])
+      return (
+        <div onClick={onClick}>
+          {swrKey && data ? 'suspense-' + (9 + Number(data)) : undefined}
+        </div>
+      )
+    }
 
-      if (data !== renderedResults[renderedResults.length - 1]) {
-        renderedResults.push(data)
-      }
+    const Section = () => {
+      const [key, setKey] = useState(0)
+      const handleClick = () => setKey(key + 1)
 
-      return <div>{data}</div>
+      return (
+        <Suspense fallback={<div onClick={handleClick}>fallback</div>}>
+          <SectionContent onClick={handleClick} swrKey={key} />
+        </Suspense>
+      )
     }
-    render(
-      <Suspense fallback={<div>fallback</div>}>
-        <Section />
-      </Suspense>
-    )
-    await act(() => new Promise(res => setTimeout(res, 210)))
 
-    expect(renderedResults).toEqual(['suspense-9'])
+    const { container } = render(<Section />)
+
+    async function clickAndWait(duration) {
+      fireEvent.click(container.firstElementChild)
+      return await act(
+        () => new Promise(resolve => setTimeout(resolve, duration))
+      )
+    }
+
+    expect(container.textContent).toMatchInlineSnapshot(`"fallback"`)
+    await clickAndWait(100)
+    expect(container.textContent).toMatchInlineSnapshot(`"suspense-10"`)
+    await clickAndWait(100)
+    expect(container.textContent).toMatchInlineSnapshot(`"fallback"`)
+    await clickAndWait(100)
+    expect(container.textContent).toMatchInlineSnapshot(`"suspense-10"`)
   })
 })