From 4078ce9c58830fecff095ab96dc41693377794dd Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=28=C2=B4=E3=83=BB=CF=89=E3=83=BB=EF=BD=80=29?=
 <HerringtonDarkholme@users.noreply.github.com>
Date: Fri, 4 Nov 2016 19:44:47 +0800
Subject: [PATCH] fix #4041, warn overriding Vue's internal methods (#4111)

* fix #4041, warn overriding Vue's internal methods

* prefer concise warning message
---
 src/core/instance/state.js                 | 10 ++++++++--
 test/unit/features/options/methods.spec.js | 10 ++++++++++
 2 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/src/core/instance/state.js b/src/core/instance/state.js
index 36a8d3fb11f..8469749349f 100644
--- a/src/core/instance/state.js
+++ b/src/core/instance/state.js
@@ -21,6 +21,8 @@ import {
   noop
 } from '../util/index'
 
+import BuiltinVue from '../index'
+
 export function initState (vm: Component) {
   vm._watchers = []
   initProps(vm)
@@ -143,12 +145,16 @@ function initMethods (vm: Component) {
   if (methods) {
     for (const key in methods) {
       vm[key] = methods[key] == null ? noop : bind(methods[key], vm)
-      if (process.env.NODE_ENV !== 'production' && methods[key] == null) {
-        warn(
+      if (process.env.NODE_ENV !== 'production') {
+        methods[key] == null && warn(
           `method "${key}" has an undefined value in the component definition. ` +
           `Did you reference the function correctly?`,
           vm
         )
+        hasOwn(BuiltinVue.prototype, key) && warn(
+          `Avoid overriding Vue's internal method "${key}".`,
+          vm
+        )
       }
     }
   }
diff --git a/test/unit/features/options/methods.spec.js b/test/unit/features/options/methods.spec.js
index 3e6991144be..d9c54a8590e 100644
--- a/test/unit/features/options/methods.spec.js
+++ b/test/unit/features/options/methods.spec.js
@@ -24,4 +24,14 @@ describe('Options methods', () => {
     })
     expect(`method "hello" has an undefined value in the component definition`).toHaveBeenWarned()
   })
+
+  it('should warn overriding builtin methods', () => {
+    new Vue({
+      methods: {
+        $emit () {
+        }
+      }
+    })
+    expect(`Avoid overriding Vue's internal method "$emit".`).toHaveBeenWarned()
+  })
 })