Question

    function abc(arg1,arg2, callback){
        console.log(arg1 + arg2) // I am doing something really interesting
        if(callback){
        callback(arg1+ arg2)
        }
    }
    function add(){
            console.log("from call back " + arguments[0])
    }

    var a =10;
    abc(1,2, add)

this works fine, but if we need to send some additional arguments to the call back, what should we do??

Here, Apart from (arg1+ arg2) I need some other arguments to be set from the caller of abc to the callback

And, what is the difference between abc(1,2,add) and abc(1,2,add()) ??

Thanks 🙂

Answer 1

• abc(1,2,add) => Giving the function argument as “function type”. This is like giving a pointer to the function for later invoking it.

• abc(1,2,add()) => Calling the add() function and giving its return value as argument.

Do you need that the callback support more than an argument? Since JavaScript is a dynamic language, just call the same callback function with more arguments:

• callback(1,2,3,4)
• callback(1,2,3,4,5)
• callback(1,2,3,4,5,6).

JavaScript isn’t strict with function signatures: functions have as many arguments as the caller gives to them.

For example, if you’ve a callback function like this:

function(a, b) {

}

And later you call it this way:

function("hello"); // Where's the second argument??

JavaScript won’t complain. Simply b will be undefined.