fix(state-key): PositionStore memory leak(fix vuejs#3445)

Author: hezedu

Diff for: src/util/push-state.js

@@ -1,7 +1,7 @@
 /* @flow */
 
 import { inBrowser } from './dom'
-import { saveScrollPosition } from './scroll'
+import { saveScrollPosition, clearPositionStore } from './scroll'
 import { genStateKey, setStateKey, getStateKey } from './state-key'
 import { extend } from './misc'
 
@@ -28,6 +28,7 @@ export function pushState (url?: string, replace?: boolean) {
   // DOM Exception 18 where it limits to 100 pushState calls
   const history = window.history
   try {
+    clearPositionStore()
     if (replace) {
       // preserve existing history state as it could be overriden by the user
       const stateCopy = extend({}, history.state)

Diff for: src/util/scroll.js

@@ -2,7 +2,7 @@
 
 import type Router from '../index'
 import { assert } from './warn'
-import { getStateKey, setStateKey } from './state-key'
+import { getStateKey, setStateKey, getCurrentStateKey } from './state-key'
 import { extend } from './misc'
 
 const positionStore = Object.create(null)
@@ -173,3 +173,12 @@ function scrollToPosition (shouldScroll, position) {
     }
   }
 }
+
+export function clearPositionStore () {
+  const key = getCurrentStateKey()
+  for (var i in positionStore) {
+    if (Number(i) > key) {
+      delete (positionStore[i])
+    }
+  }
+}

Diff for: src/util/state-key.js

@@ -1,22 +1,24 @@
 /* @flow */
 import { inBrowser } from './dom'
 
-// use User Timing api (if present) for more accurate key precision
-const Time =
-  inBrowser && window.performance && window.performance.now
-    ? window.performance
-    : Date
+export function getCurrentStateKey (): number {
+  const state = window.history.state
+  if (state && typeof state.key === 'number') {
+    return state.key
+  }
+  return 1
+}
 
-export function genStateKey (): string {
-  return Time.now().toFixed(3)
+export function genStateKey (): number {
+  return getCurrentStateKey() + 1
 }
 
-let _key: string = genStateKey()
+let _key: number = inBrowser ? getCurrentStateKey() : -1
 
 export function getStateKey () {
   return _key
 }
 
-export function setStateKey (key: string) {
+export function setStateKey (key: number) {
   return (_key = key)
 }