text: 
  function largestOfFour(arr) {
    var newArr = [];
    for(var elem in arr){
     // It will be better to use another variable to assign the result because RHS is no and LHS is an object i.e., array.
     //arr[elem] = arr[elem].reduce(function(a, b){ return a > b ? a:b;});
  
      newArr[elem] = arr[elem].reduce(function(a, b){ return a > b ? a:b;});
  
  
    }
    return newArr;
  }
  
  largestOfFour([[4, 5, 1, 3], [13, 27, 18, 26], [32, 35, 37, 39], [1000, 1001, 857, 1]]);
  