找出二维数组各数组中最大数并组成新数组

function largestOfFour(arr) {
// You can do this!

var array = arr[0];
for (var i = 0; i < arr.length; i++){
var num = 0;
for (var j = 0; j < 4; j++){
if (num <= arr[i][j]){
num = arr[i][j];
array[i] = num;
}
}
}

return array;
}

largestOfFour([[13, 27, 18, 26], [4, 5, 1, 3], [32, 35, 37, 39], [1000, 1001, 857, 1]]);