ensure hashchange listener is always created (fix #853)

Author: yyx990803

src/history/hash.js

@@ -8,6 +8,9 @@ import { cleanPath } from '../util/path'
 export class HashHistory extends History {
   constructor (router: VueRouter, base: ?string, fallback: boolean) {
     super(router, base)
+    window.addEventListener('hashchange', () => {
+      this.onHashChange()
+    })
 
     // check history fallback deeplinking
     if (fallback && this.checkFallback()) {

src/index.js

@@ -72,11 +72,7 @@ export default class VueRouter {
     if (history instanceof HTML5History) {
       history.transitionTo(getLocation(history.base))
     } else if (history instanceof HashHistory) {
-      history.transitionTo(getHash(), () => {
-        window.addEventListener('hashchange', () => {
-          history.onHashChange()
-        })
-      })
+      history.transitionTo(getHash())
     }
 
     history.listen(route => {