File size: 4,868 Bytes
b2cad4f
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
diff --git a/packages/next/src/client/components/app-router.tsx b/packages/next/src/client/components/app-router.tsx
index d043d825cb..446c8b277b 100644
--- a/packages/next/src/client/components/app-router.tsx
+++ b/packages/next/src/client/components/app-router.tsx
@@ -56,6 +56,59 @@ const globalMutable: {
   pendingMpaPath?: string
 } = {}
 
+// A Back/Forward press before the router's popstate listener exists moves the
+// browser to a different history entry than the one the document was activated
+// on, and the resulting popstate fires with nobody listening. The activation
+// entry is fixed for the document's lifetime and entry keys are stable across
+// replaceState, so until the listener is installed a key mismatch means a
+// traversal went unobserved.
+function hasMissedTraversal(): boolean {
+  if (typeof window.navigation === 'undefined') {
+    return false
+  }
+  const activationEntry = window.navigation.activation?.entry
+  const currentEntry = window.navigation.currentEntry
+  return (
+    activationEntry != null &&
+    currentEntry != null &&
+    activationEntry.key !== currentEntry.key &&
+    // Only entries written by the app router can be restored; on any other
+    // entry the traversal is left unhandled, as before.
+    window.history.state?.__NA === true
+  )
+}
+
+let checkedMissedTraversalBeforeHistoryWrite = false
+let checkedMissedTraversalBeforeReplay = false
+
+/**
+ * Handles a popstate event (or one that was missed before hydration).
+ * By default dispatches ACTION_RESTORE, however if the history entry was not
+ * pushed/replaced by app-router it will reload the page.
+ * That case can happen when the old router injected the history entry.
+ */
+function handlePopState(state: PopStateEvent['state']): void {
+  if (!state) {
+    // TODO-APP: this case only happens when pushState/replaceState was called outside of Next.js. It should probably reload the page in this case.
+    return
+  }
+
+  // This case happens when the history entry was pushed by the `pages` router.
+  if (!state.__NA) {
+    window.location.reload()
+    return
+  }
+
+  // TODO-APP: Ideally the back button should not use startTransition as it should apply the updates synchronously
+  // Without startTransition works if the cache is there for this path
+  startTransition(() => {
+    dispatchTraverseAction(
+      window.location.href,
+      state.__PRIVATE_NEXTJS_INTERNALS_TREE
+    )
+  })
+}
+
 function HistoryUpdater({
   appRouterState,
 }: {
@@ -70,6 +123,16 @@ function HistoryUpdater({
 
     const { tree, pushRef, canonicalUrl, renderedSearch } = appRouterState
 
+    if (!checkedMissedTraversalBeforeHistoryWrite) {
+      checkedMissedTraversalBeforeHistoryWrite = true
+      if (hasMissedTraversal()) {
+        // Skip the write: it would overwrite the traversed-to entry's state.
+        // The tree was rendered even though the history write is skipped.
+        setLastCommittedTree(tree)
+        return
+      }
+    }
+
     const appHistoryState: AppHistoryState = {
       tree,
       renderedSearch,
@@ -371,35 +434,17 @@ function Router({
       return originalReplaceState(data, _unused, url)
     }
 
-    /**
-     * Handle popstate event, this is used to handle back/forward in the browser.
-     * By default dispatches ACTION_RESTORE, however if the history entry was not pushed/replaced by app-router it will reload the page.
-     * That case can happen when the old router injected the history entry.
-     */
-    const onPopState = (event: PopStateEvent) => {
-      if (!event.state) {
-        // TODO-APP: this case only happens when pushState/replaceState was called outside of Next.js. It should probably reload the page in this case.
-        return
-      }
+    const onPopState = (event: PopStateEvent) => handlePopState(event.state)
 
-      // This case happens when the history entry was pushed by the `pages` router.
-      if (!event.state.__NA) {
-        window.location.reload()
-        return
-      }
+    window.addEventListener('popstate', onPopState)
 
-      // TODO-APP: Ideally the back button should not use startTransition as it should apply the updates synchronously
-      // Without startTransition works if the cache is there for this path
-      startTransition(() => {
-        dispatchTraverseAction(
-          window.location.href,
-          event.state.__PRIVATE_NEXTJS_INTERNALS_TREE
-        )
-      })
+    if (!checkedMissedTraversalBeforeReplay) {
+      checkedMissedTraversalBeforeReplay = true
+      if (hasMissedTraversal()) {
+        handlePopState(window.history.state)
+      }
     }
 
-    // Register popstate event to call onPopstate.
-    window.addEventListener('popstate', onPopState)
     return () => {
       window.history.pushState = originalPushState
       window.history.replaceState = originalReplaceState