[removed] Optional callback? [duplicate]

Answer 1

Ensure the callback is a function, and then invoke it.

function myFunction(arg1, arg2, callback){
    // do something

    typeof callback == "function" && callback();
}

If you want more control over invoking it, use call(), apply(), bind() (whatever achieves your goal).

Answer 2

Simple, just check if callback is defined before you call it.

function myFunction(arg1, arg2, callback){
    // do something

    if (callback) {
        callback();
    }
}