When using using reduce with ternary inside a map, I seem to have troubles

this is to return an array of numbers that are the highest value of the arrays inside of the base array. I can get it to work when i use for statements. But I have tried to simplify it, and can’t work out why it doesn’t work. any help would be appriciated.

function largestOfFour(arr) {
  return arr.map((x) => x.reduce((a, c) =>  c > a ? c : a, 0));
}

let test = [[1, 2, 3][4, 5, 6][7, 8, 9]]
console.log(largestOfFour(test)) // expected output[3, 6, 9] the largest number from each array

>Solution :

If you have values smaller than zero, you need to remove the start value

x.reduce((a, c) =>  c > a ? c : a, 0)
                                   ^

or use a very small start value, like -Number.MAX_VALUE.