feat($core): support async enhanceApp (close vuejs#2074)

Author: meteorlxy

packages/@vuepress/core/lib/client/app.js

@@ -59,7 +59,7 @@ Vue.prototype.$withBase = function (path) {
   }
 }
 
-export function createApp (isServer) {
+export async function createApp (isServer) {
   const routerBase = typeof window !== 'undefined' && window.__VUEPRESS_ROUTER_BASE__
     ? window.__VUEPRESS_ROUTER_BASE__
     : (siteData.routerBase || siteData.base)
@@ -90,11 +90,11 @@ export function createApp (isServer) {
   const options = {}
 
   try {
-    appEnhancers.forEach(enhancer => {
-      if (typeof enhancer === 'function') {
-        enhancer({ Vue, options, router, siteData, isServer })
-      }
-    })
+    await Promise.all(
+      appEnhancers
+        .filter(enhancer => typeof enhancer === 'function')
+        .map(enhancer => enhancer({ Vue, options, router, siteData, isServer }))
+    )
   } catch (e) {
     console.error(e)
   }

packages/@vuepress/core/lib/client/clientEntry.js

@@ -2,13 +2,13 @@
 
 import { createApp } from './app'
 
-const { app, router } = createApp(false /* isServer */)
-
 window.__VUEPRESS__ = {
   version: VUEPRESS_VERSION,
   hash: LAST_COMMIT_HASH
 }
 
-router.onReady(() => {
-  app.$mount('#app')
+createApp(false /* isServer */).then(({ app, router }) => {
+  router.onReady(() => {
+    app.$mount('#app')
+  })
 })

packages/@vuepress/core/lib/client/serverEntry.js

@@ -1,14 +1,15 @@
 import { createApp } from './app'
 
 export default context => new Promise((resolve, reject) => {
-  const { app, router } = createApp(true /* isServer */)
-  const { url } = context
-  const { fullPath } = router.resolve(url).route
+  createApp(true /* isServer */).then(({ app, router }) => {
+    const { url } = context
+    const { fullPath } = router.resolve(url).route
 
-  if (fullPath !== url) {
-    return reject({ url: fullPath })
-  }
+    if (fullPath !== url) {
+      return reject({ url: fullPath })
+    }
 
-  router.push(url)
-  router.onReady(() => resolve(app))
+    router.push(url)
+    router.onReady(() => resolve(app))
+  })
 })