optimize scroll position saving (fix #1145)

Author: yyx990803

src/util/push-state.js

@@ -38,6 +38,7 @@ export function setStateKey (key: string) {
 }
 
 export function pushState (url?: string, replace?: boolean) {
+  saveScrollPosition()
   // try...catch the pushState call to get around Safari
   // DOM Exception 18 where it limits to 100 pushState calls
   const history = window.history
@@ -48,7 +49,6 @@ export function pushState (url?: string, replace?: boolean) {
       _key = genKey()
       history.pushState({ key: _key }, '', url)
     }
-    saveScrollPosition()
   } catch (e) {
     window.location[replace ? 'replace' : 'assign'](url)
   }

src/util/scroll.js

@@ -8,12 +8,11 @@ const positionStore = Object.create(null)
 
 export function setupScroll () {
   window.addEventListener('popstate', e => {
+    saveScrollPosition()
     if (e.state && e.state.key) {
       setStateKey(e.state.key)
     }
   })
-
-  window.addEventListener('scroll', saveScrollPosition)
 }
 
 export function handleScroll (