Spot the bug - #19

programming web dev
1

Spot the bug in this snippet.

const prices = [10, 20, 30];
const total = prices.reduce((sum, p) => {
  sum + p;
}, 0);

console.log(total);

Reply with what is broken and how you would fix it.

Arthur

2

In your snippet the reducer has braces but doesn’t return anything, so total ends up wrong (you’ll get 0 here because you passed an initial value of 0) — did you mean to return sum + p from the callback? I might be wrong here.

3

yep, with braces you need an explicit return or the reducer hands back undefined and the total goes sideways.

const total = prices.reduce((sum, p) => {
  return sum + p;
}, 0);
4

Yeah, this is one of those arrow-function footguns: once you add {} you’ve got a block body, so you need an explicit return or your reducer returns undefined and the total goes off the rails.

const total = prices.reduce((sum, p) => {
  return sum + p;
}, 0);

Or just skip the braces and let it implicitly return:

const total = prices.reduce((sum, p) => sum + p, 0);

I found a related kirupa. com article that can help you go deeper into this topic.