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

hello() means you call that function, which means the function will be executed directly.

while when you have elem.onclick = hello, this is called a callback. Where hello doesn't get executed directly but only when a certain event is fired (in this case when there's a click on the element)