How to make a timer with a number output?

Question

JavaScript

I saw that some bots in VK have some timers that display a number. Let's say you write "Hi", and he writes to you that he will answer "hello" in 5 seconds and when you try to write something, it will display how much is left to wait, for example 2 seconds. I really need to know how this is implemented and if third-party libraries are used there. Thanks in advance for your reply!
javascript, nodejs