How do you trigger a JavaScript event from CSS pseudo event without using jQuery?

I want a JavaScript event to happen when a CSS pseudo-event takes place. Here's an example:

element:hover {background-color: red;} I want it to run this code block below when the element also turns red: console.log("Hello, world!")

I'm not sure if this is really possible without using jQuery, but if it is, tell me how to do this.