Vue.js refs are undefined, even though this.$refs shows correctly

In case that this.$refs shows undefined in vuejs application, use v-show instead of v-if solves the problem:

use the following

<div v-show="!isLoading"> 
   <GMap ref="mapRef" />
 </div>

instead of

<div v-if="!isLoading"> 
   <GMap ref="mapRef" />
 </div>