Display always fixed number of images, but if there is more images in gallery, show the number of remaining on the last displayed item. Code Snippet included.
Unlike whole tutorial, here is rewritten source code available, using Vue.js webpack simple template.
The last direction, how Vue.js components can communicate is child->child, or non parent->child respectively. In simple cases, central event bus fits for this type of communication.
While there is nothing like two-way component communicaton in Vue.js, each data flow must be defined separately.