I am making an event listener where I need to put a function but I am having problems in doing so

Question

I have made a function outside the event listener:

function nextSequence(){
  Some something here
}

Then I had an event listener:

$(document).keydown( 

after this I used to make a nameless function earlier but now I want to input a function that has been earlier made. So how do I do it

I tried

$(document).keydown(nextSequence ())

But nothing happened