Need help about reduce()

// My question
I have a code like this and I understand a bit about reducing () but I still don’t understand how to set the specific variable in this case ‘’ a ‘’ and ‘’ b ‘’, what role do they have? How do these two variables add up the total numbers in my array?

// My code
const mytest = arr => arr.reduce((a,b) => a + b, 0);
console.log(mytest([1,2,3,4]));

Reduce callback takes (in this case) two paramaters a and b, where a is the accumulator and b is the current value.

Naming could be anything you want.

You can think of it as an for loop with a variable outside (a) that you assign with += in each iteration (b)

In this case running the reducer,
a = 0
b = 1

a = 1
b = 2

a = 3
b = 3

a = 6
b = 4

Returns 10.
The 0 provided is the initial value set for the accumulator (a), which in this case is a starting value of 0.
If you write a 10 there instead it would return 20.

3 Likes

What a perfect answer, I understand, thanks