Javascript - execute multiple different [removed]

Question

I am facing a little problem here. I have basic knowledge about Javascript and i want to do the following:

Right now, when you scroll down, the menu will get smaller

Answer 1

You override onscroll function by doing window.onscroll = blabla

You can do :

window.onscroll = function() {
  effects();
  test();
}

or

window.addEventListener('scroll', effects);
window.addEventListener('scroll', test);