CODE EXAMPLE FOR JAVASCRIPT

find the second largest number in an array javascript

function largestOfFour(mainArray) {
  return mainArray.map(function (subArray){
    return subArray.reduce(function (previousLargestNumber, currentLargestNumber) {
      return (currentLargestNumber > previousLargestNumber) ? currentLargestNumber : previousLargestNumber;
    }, 0);
  });
}
largestOfFour([[4, 5, 1, 3], [13, 27, 18, 26], [32, 35, 37, 39], [1000, 1001, 857, 1]]);