An empty parameter list is a set of empty parenthesis
The body can either be a single expression or curly braces with statements in it. Which one of those you use doesn’t affect how you write the parameter list. It makes no difference which you use so for the purpose of asking this you should pick the same one for “both cases”, except there aren’t two such cases
The things you’re changing are independent of each other. They’re all arrow functions, you’re not converting between two kinds
You might wanna have a look at msdn’s page for arrow functions, reading a relatively complete and correct description may be better than playing whack-a-mole with your understanding
(and you may generally want to refer to msdn for finding out how things are written or behave or otherwise, in javascript)