I'm just wondering if anyone could clarify why Square Brackets are being used during a Function call-back in JavaScript?

Question

So, I'm currently working my way through JavaScript and often find myself getting the 'information overload' block regarding information...

I was hoping someone could clarify for me that why, if I write the below Function, upon its call-back I require square brackets inside of the function call-back parenthesis?

function printReverse(arr){
    for(var i = arr.length - 1; i >= 0; i--){
        console.log(arr[i]);
    }
}

Function Call-back:

printReverse([3,4,5,6])

The way that I'm wanting to describe this is: The square brackets are used so that the numbers within are defined as the array variables parameters. As they are not defined due to not knowing how many we may need, it is defined based off of the users input.

But why the square brackets? And why do I get an error when using just the parenthesis? And is this to do with JavaScript recognising variable elements inside of square brackets as 'Array values'?

Please feel free to adjust any logic etc. I just like to break things down to literal basics for my notes! Any additional reading etc is also welcome.

Thank you.

Answer 1

A callback is when you pass a function as an argument (which then gets called by the function you pass it to). There is no callback here.

Square brackets, in this context, denote an array.

The array is the value that is passed to the arr argument.

Without the square brackets you don’t have an array and you pass 4 separate arguments instead. The code tries to treat the first one as an array, but it is a number so this errors.