Fix invalid ping response throwing error in client (#6397)

packages/next/client/on-demand-entries-client.js

@@ -34,18 +34,20 @@ export default async ({ assetPrefix }) => {
     }
 
     evtSource.onmessage = event => {
-      const payload = JSON.parse(event.data)
-      if (payload.invalid) {
-        // Payload can be invalid even if the page does not exist.
-        // So, we need to make sure it exists before reloading.
-        fetch(location.href, {
-          credentials: 'same-origin'
-        }).then(pageRes => {
-          if (pageRes.status === 200) {
-            location.reload()
-          }
-        })
-      }
+      try {
+        const payload = JSON.parse(event.data)
+        if (payload.invalid) {
+          // Payload can be invalid even if the page does not exist.
+          // So, we need to make sure it exists before reloading.
+          fetch(location.href, {
+            credentials: 'same-origin'
+          }).then(pageRes => {
+            if (pageRes.status === 200) {
+              location.reload()
+            }
+          })
+        }
+      } catch (_) { /* noop */ }
     }
   }
 

packages/next/server/on-demand-entry-handler.js

@@ -303,6 +303,7 @@ export default function onDemandEntryHandler (devMiddleware, multiCompiler, {
 
           const runPing = () => {
             const data = handlePing(query.page)
+            if (!data) return
             res.write('data: ' + JSON.stringify(data) + '\n\n')
           }
           const pingInterval = setInterval(() => runPing(), 5000)