How to make a function only fire when 3 buttons are clicked in Vanilla Javascript?

I couldn’t figure this out or find anything on this on the web.
Basically how would you write code for this:
I have 3 buttons, and I need to click all of them before the function fires.
I know how to have each button do the same thing, but I want it so I have to click all 3 for it to do anything.

If you could give me any example code of this I can find a way to implement it into my project.

If you need me to elaborate let me know.
Thanks!