How to get the number of the clicked element in js?

Question

css

https://jsfiddle.net/crmyc4d1/2/
I want to make tabs on pure js, with an unknown number of tabs and content data, in case a few more are added
to jq, there is a useful index function...
I'm thinking how to do the same on native js?
I'm thinking of doing something like... add data-* to some clicked element, and then count from the first element until I encounter that data-*
How would you do it?

Answer 1

FullPage will probably do , it's the one used on the site above.

Answer 2

https://jsfiddle.net/yarkov_aleksei/crmyc4d1/3/