Use hasOwnProperty in getterFor

This avoids the case in which 'watch' is somewhere on the prototype
chain, as for instance in Firefox which includes a 'watch' method
on Object.prototype.

Author: foxbenjaminfox

CHANGELOG.md

@@ -2,6 +2,7 @@
 <!-- DON'T EDIT THIS SECTION, INSTEAD RE-RUN doctoc TO UPDATE -->
 # Changelog
 
+- [v3.1.3](#v313)
 - [v3.1.1](#v311)
 - [v3.1.0](#v310)
 - [v3.0.1](#v301)
@@ -16,6 +17,10 @@
 
 <!-- END doctoc generated TOC please keep comment here to allow auto update -->
 
+### v3.1.3
+  * Fix a bug where extra properties on `Object.prototype` would be
+    considered relevent to `vue-async-computed`.
+
 ### v3.1.1
   * Fix bug where `vue-async-computed` wouldn't find async computed
     properties that were further up the prototype chain.

src/index.js

@@ -74,7 +74,7 @@ function getterFor (fn) {
 
   let getter = fn.get
 
-  if (fn.watch) {
+  if (fn.hasOwnProperty('watch')) {
     getter = function getter () {
       fn.watch.call(this)
       return fn.get(this)