refactor: remove circular dependency

Author: posva

src/util/push-state.js

@@ -2,40 +2,24 @@
 
 import { inBrowser } from './dom'
 import { saveScrollPosition } from './scroll'
+import { genStateKey, setStateKey, getStateKey } from './state-key'
+
+export const supportsPushState =
+  inBrowser &&
+  (function () {
+    const ua = window.navigator.userAgent
+
+    if (
+      (ua.indexOf('Android 2.') !== -1 || ua.indexOf('Android 4.0') !== -1) &&
+      ua.indexOf('Mobile Safari') !== -1 &&
+      ua.indexOf('Chrome') === -1 &&
+      ua.indexOf('Windows Phone') === -1
+    ) {
+      return false
+    }
 
-export const supportsPushState = inBrowser && (function () {
-  const ua = window.navigator.userAgent
-
-  if (
-    (ua.indexOf('Android 2.') !== -1 || ua.indexOf('Android 4.0') !== -1) &&
-    ua.indexOf('Mobile Safari') !== -1 &&
-    ua.indexOf('Chrome') === -1 &&
-    ua.indexOf('Windows Phone') === -1
-  ) {
-    return false
-  }
-
-  return window.history && 'pushState' in window.history
-})()
-
-// use User Timing api (if present) for more accurate key precision
-const Time = inBrowser && window.performance && window.performance.now
-  ? window.performance
-  : Date
-
-let _key: string = genKey()
-
-function genKey (): string {
-  return Time.now().toFixed(3)
-}
-
-export function getStateKey () {
-  return _key
-}
-
-export function setStateKey (key: string) {
-  _key = key
-}
+    return window.history && 'pushState' in window.history
+  })()
 
 export function pushState (url?: string, replace?: boolean) {
   saveScrollPosition()
@@ -44,10 +28,9 @@ export function pushState (url?: string, replace?: boolean) {
   const history = window.history
   try {
     if (replace) {
-      history.replaceState({ key: _key }, '', url)
+      history.replaceState({ key: getStateKey() }, '', url)
     } else {
-      _key = genKey()
-      history.pushState({ key: _key }, '', url)
+      history.pushState({ key: setStateKey(genStateKey()) }, '', url)
     }
   } catch (e) {
     window.location[replace ? 'replace' : 'assign'](url)

src/util/scroll.js

@@ -2,7 +2,7 @@
 
 import type Router from '../index'
 import { assert } from './warn'
-import { getStateKey, setStateKey } from './push-state'
+import { getStateKey, setStateKey } from './state-key'
 
 const positionStore = Object.create(null)
 

src/util/state-key.js

@@ -0,0 +1,22 @@
+/* @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 genStateKey (): string {
+  return Time.now().toFixed(3)
+}
+
+let _key: string = genStateKey()
+
+export function getStateKey () {
+  return _key
+}
+
+export function setStateKey (key: string) {
+  return (_key = key)
+}