fix: sync cache only on compare returns true

Author: huozhi

src/use-swr.ts

@@ -475,7 +475,6 @@ function useSWR<Data = any, Error = any>(
           return false
         }
 
-        cache.set(key, newData)
         cache.set(keyErr, undefined)
         cache.set(keyValidating, false)
 
@@ -492,6 +491,7 @@ function useSWR<Data = any, Error = any>(
           // deep compare to avoid extra re-render
           // data changed
           newState.data = newData
+          cache.set(key, newData)
         }
 
         // merge the new state

test/use-swr.test.tsx

@@ -686,16 +686,17 @@ describe('useSWR - refresh', () => {
     )
   })
 
-  it('should allow use custom isEqual method', async () => {
+  it('should allow use custom compare method', async () => {
+    const key = 'dynamic-11'
     function Page() {
       const { data, revalidate } = useSWR(
-        'dynamic-11',
+        key,
         () => ({
           timestamp: +new Date(),
           version: '1.0'
         }),
         {
-          compare: function isEqual(a, b) {
+          compare: function compare(a, b) {
             if (a === b) {
               return true
             }
@@ -724,6 +725,9 @@ describe('useSWR - refresh', () => {
       return new Promise(res => setTimeout(res, 1))
     })
     const secondContent = container.firstChild.textContent
+    const cachedData = cache.get(key)
+
+    expect(cachedData.timestamp.toString()).toEqual(secondContent)
     expect(firstContent).toEqual(secondContent)
   })