Need a little help understanding reduce !☻

Hello there !
I have trouble understanding the different parameters of the reduce callback function, look at this :

var array = [4,5,6,7,8];
var singleVal = 0;

// Only change code below this line.
singleVal = array.reduce(function(previousVal,currentVal){
  return previousVal + currentVal;
}, 0);

I’m talking about “previousVal” and “currentVal”, can we just add whatever number of parameters, like I can put (previousVal,currentVal,afterVal,afterVal2,afterVal3) ?

And what they refer to ?
I mean when we are at the first iteration, it’s previousVal (= 0) + currentVal (= 4) right?

Thank’s if someone respond :slight_smile:
(sorry for the grammar mistakes if there is).

No.
The callback function will only know how to handle the 4 parameters described here.

Thank’s guys it helped ! I’ll sleep less idiot tonight