When to use () after a callback function name? [duplicate]

Answer 1

anotherFunction on its own is a reference to the function itself.

anotherFunction() calls the function and results in whatever the function returns.

This is an extremely massive difference.

It's like the difference between:

function test() {
    alert("Hello!");
}
setTimeout(test,1000); // called after one second
setTimeout(test(),1000); // called immediately, timeout fails.

Answer 2

You should use the first one. This is because the () execute the function defined before them. If you use the first one, the callback anotherFunction is only called when you want it to. JQuery would do something like anotherFunction (in a var named callback) callback()

Answer 3

The first one passes the actual function; the second passes the returned value of the function.

I'm unclear on the meaning of your final question.

Answer 4

anotherFunction is a reference to a function. anotherFunction() is that function evaluated with no arguments (and therefore has no reference to anotherFunction). The only reason you'd want to call a function to be passed where a function is expected is if that function returned another function.

Answer 5

The difference is between passing function reference and calling that function.

The first case (probably correct) means: call this function when event occurs.

The second will be interpreted as: call this function immediately and use whatever was returned as a callback. It'll better be a function that I can call later.

The latter case will only work if the function is defined as follows:

function anotherFunction() {
    return function() {
        //real handler
    }
}