Next.js clear: () => void;

Question

I there, I am learning web development. I found on GitHub code for ecommerce with this piece of code. Can you please explain me how is working keyword void in Next.js?

I think I saw key word "void" in C++ class, what is doing "void" in next.js? Thank you.

type StoreType = {
  ..
  addOnCart: (item: Product) => void;
  increaseQuantity: (id: Product['id']) => void;
  decreaseQuantity: (id: Product['id']) => void;
  clear: () => void;
}