Gridsome - Docc add a zoom on embedded images in markdown file

Question

I use Gridsome and the Docc starter for build an online documentation.

I like to provide some zoomable screenshots. So I use the image tags in my md files

How I can add a zoom function on to the image tags?

This is my code:

<img click="zoomImage('/images/screenshots/screenshot1.png')" style="cursor: zoom-in" src="/images/screenshots/screenshot1.png" width="100px">

Can't execute my zoomImage() function. On which place I have do defined my zoom function in the vue source?