Return Largest Numbers in Arrays (freeCodeCamp challenge)

largest_numbers.txt

//Return an array consisting of the largest number from each provided sub-array. 

function largestOfFour(arr) {
  
  var largest = arr.map(function(val){
    return Math.max(...val);              // ES6 syntax, equivalent to "return Math.max.apply(null, val);"
  });
  
  return largest;
}

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