From 547e4f98a7cfc56eadc900d5266ee096a7a88703 Mon Sep 17 00:00:00 2001
From: ULIVZ <472590061@qq.com>
Date: Mon, 11 Mar 2019 01:40:53 +0800
Subject: [PATCH] feat($core): optional callback when socket connection is
 ready under dev.

---
 packages/@vuepress/core/lib/node/App.js       | 4 ++--
 packages/@vuepress/core/lib/node/dev/index.js | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/packages/@vuepress/core/lib/node/App.js b/packages/@vuepress/core/lib/node/App.js
index 4b1ab57f28..bae5b61557 100755
--- a/packages/@vuepress/core/lib/node/App.js
+++ b/packages/@vuepress/core/lib/node/App.js
@@ -451,7 +451,7 @@ module.exports = class App {
    * @api public
    */
 
-  async dev () {
+  async dev (callback) {
     this.isProd = false
     this.devProcess = new DevProcess(this)
     await this.devProcess.process()
@@ -462,7 +462,7 @@ module.exports = class App {
         this.process()
       })
       .createServer()
-      .listen()
+      .listen(callback)
   }
 
   /**
diff --git a/packages/@vuepress/core/lib/node/dev/index.js b/packages/@vuepress/core/lib/node/dev/index.js
index 4267b3bfc0..9f2cf2703c 100644
--- a/packages/@vuepress/core/lib/node/dev/index.js
+++ b/packages/@vuepress/core/lib/node/dev/index.js
@@ -250,7 +250,7 @@ module.exports = class DevProcess extends EventEmitter {
 
   listen (callback) {
     this.server.listen(this.port, this.host, (err) => {
-      if (callback) {
+      if (typeof callback === 'function') {
         callback(err)
       }
     })