What is the difference between a function call and function reference?

Question

I have the following function

function hello() {
 alert(\"hi!\");
}

Take this piece of code:

var elem = document.getElem         


        

Answer 1

How can I know where I'm supposed to give a reference to the function, and when I'm supposed to actually call it?

Do you need the function to run now?

Than add the () to execute it

Do you need to function to be referenced so it is called later?

Do not add the ().