User clicks javascript ?

I'm trying to create something for a website i'm working on but i'm a bit unsure on how I go about doing it.

So I was going to create an events page. Next to each event there would be a button saying "I'm going to this event" when the user clicks on the button +1 will be added to the number of people who are going which will be displayed using text like this "209 people are going". Any suggestions on what languages I would need to use ? Thanks