From 9aaf29e3a0c774bdaa142de8c31f8f5f54c9f687 Mon Sep 17 00:00:00 2001
From: Guilherme Eiras <guialbertoeiras@hotmail.com>
Date: Mon, 20 Nov 2017 20:26:17 -0200
Subject: [PATCH 1/2] chore: warn properties that starts with $ or _

close #7070
---
 src/core/instance/state.js                     | 9 ++++++++-
 test/unit/features/instance/properties.spec.js | 9 +++++++++
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/src/core/instance/state.js b/src/core/instance/state.js
index 4fa6f15bac8..508b304be3a 100644
--- a/src/core/instance/state.js
+++ b/src/core/instance/state.js
@@ -141,7 +141,14 @@ function initData (vm: Component) {
         `Use prop default value instead.`,
         vm
       )
-    } else if (!isReserved(key)) {
+    } else if (isReserved(key)) {
+      warn(
+        `Property "${key}" will not be proxied on the instance because it ` +
+        `may conflict with Vue's internal properties. You will have to access it as ` +
+        `"vm.$data.${key}". Avoid defining component properties that start with _ or $.`,
+        vm
+      )
+    } else {
       proxy(vm, `_data`, key)
     }
   }
diff --git a/test/unit/features/instance/properties.spec.js b/test/unit/features/instance/properties.spec.js
index 02aca12fcfa..5225b76c537 100644
--- a/test/unit/features/instance/properties.spec.js
+++ b/test/unit/features/instance/properties.spec.js
@@ -200,4 +200,13 @@ describe('Instance properties', () => {
     vm.$listeners = {}
     expect(`$listeners is readonly`).toHaveBeenWarned()
   })
+
+  it('warn data properties that start with _ or $', () => {
+    new Vue({
+      data: { $a: 'a', _b: 'b' },
+      template: '<div></div>'
+    }).$mount()
+    expect(`Property "$a" will not be proxied on the instance`).toHaveBeenWarned()
+    expect(`Property "_b" will not be proxied on the instance`).toHaveBeenWarned()
+  })
 })

From e5950a3eb126cd01475e216c1dd180c5165461d0 Mon Sep 17 00:00:00 2001
From: Guilherme Eiras <guialbertoeiras@hotmail.com>
Date: Mon, 20 Nov 2017 21:20:23 -0200
Subject: [PATCH 2/2] skip warning in production

---
 src/core/instance/state.js | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/src/core/instance/state.js b/src/core/instance/state.js
index 508b304be3a..fe09c733c49 100644
--- a/src/core/instance/state.js
+++ b/src/core/instance/state.js
@@ -142,12 +142,14 @@ function initData (vm: Component) {
         vm
       )
     } else if (isReserved(key)) {
-      warn(
-        `Property "${key}" will not be proxied on the instance because it ` +
-        `may conflict with Vue's internal properties. You will have to access it as ` +
-        `"vm.$data.${key}". Avoid defining component properties that start with _ or $.`,
-        vm
-      )
+      if (process.env.NODE_ENV !== 'production') {
+        warn(
+          `Property "${key}" will not be proxied on the instance because it ` +
+          `may conflict with Vue's internal properties. You will have to access it as ` +
+          `"vm.$data.${key}". Avoid defining component properties that start with _ or $.`,
+          vm
+        )
+      }
     } else {
       proxy(vm, `_data`, key)
     }