How to do this calculation in modx?

Question

MODX

How to make it so that when you click on a city, all other cities disappear and the selected city is active (the city of the sender)
and how to make it so that when you select a city, a list of other cities is displayed where to send

Answer 1

Good afternoon!
The question is very similar to: "I know the color table and some html tags, how to make a social network for 3 million users with 99.9% uptime?" You first decide what you want to do. Next, determine if you can do it yourself (at least partially). If yes, then do what you can, and then ask, no - look for ready-made solutions or order from other developers.
This is me to the fact that you do not have a question, but rather a suggestion "do it for me" :)