Adding interactions to d3.js chart

Hello :slight_smile:

For my first Ionic project, I am working on an application which involves a data set. I am trying to visualize the data using d3.js, and have succeeded in generating a static chart by following an awesome example presented on GitHub:

Now, I am trying to add some interaction to this chart which would involve a marker that determines the current position in the chart, as show here:
In my case, I do not need the data to change dynamically; I have static data that I want to visualise.

Could someone please guide me towards doing this, and at least give me a starting point? Iā€™m struggling with knowing where to place the event handlers in my code.

I am fairly new to front-end development. Any help would be greatly appreciated .