In JavaScript, does it make a difference if I call a function with parentheses?

Question

I noticed a difference when calling a function with empty parentheses, or without any parentheses at all. However, I am not passing any arguments to the function so I wonder

Answer 1

I'm 6 years late but I feel this could have been explained a lot simpler than the above answers.

So here is the TLDR; or bird's eye view when calling functions using and not using ()'s

Lets take this function for example:

function foo(){
return 123;
}

---

if you log "foo" - without ()

console.log(foo); 

---outout------
function foo(){
return 123;
}

Using no () means to fetch the function itself. You would do this if you want it to be passed along as a callback.

---

if you log "foo()" - with ()

console.log(foo());
-----output-----
 123

Using () after a function means to execute the function and return it's value.