From 724a59348fa2036d5184ce65bef211d24440ee11 Mon Sep 17 00:00:00 2001
From: Darius Tall <kingdaro@gmail.com>
Date: Sun, 11 Sep 2016 10:54:47 -0400
Subject: [PATCH] Add undefined check for instance methods (#3656)

* add undefined check for instance methods

* added a warning for undefined methods

* add production ENV check
---
 src/core/instance/state.js | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/core/instance/state.js b/src/core/instance/state.js
index b6a104f0..8a7545f9 100644
--- a/src/core/instance/state.js
+++ b/src/core/instance/state.js
@@ -142,7 +142,11 @@ function initMethods (vm: Component) {
   const methods = vm.$options.methods
   if (methods) {
     for (const key in methods) {
-      vm[key] = bind(methods[key], vm)
+      if (methods[key] != null) {
+        vm[key] = bind(methods[key], vm)
+      } else if (process.env.NODE_ENV !== 'production') {
+        warn(`The method ${key} on vue instance is undefined.`, vm)
+      }
     }
   }
 }