Finding The Highest Numbers in A Double Deep Array

Highest_Numbers_in_Double_Deep_Array.js

function largestOfFour(arr) {
   var largestNumber = [0,0,0,0];
   for(var arrayIndex = 0; arrayIndex < arr.length; arrayIndex++) {
    for(var subArrayIndex = 0; subArrayIndex < arr[arrayIndex].length; subArrayIndex++) {
       if(arr[arrayIndex][subArrayIndex] > largestNumber[arrayIndex]) {         
          largestNumber[arrayIndex] = arr[arrayIndex][subArrayIndex];
        }
    }
 }
 return largestNumber;
}
largestOfFour([[4, 5, 1, 3], [13, 27, 18, 26], [32, 35, 37, 39], [1000, 1001, 857, 1]]);