Max_Avg_Sub_Array_KadaneMethod.js

var maxSequence = function(arr){

  var curr_max = 0, max_so_far = 0;

  for(var i = 0; i < arr.length; i++){  
    curr_max = Math.max(0, curr_max + arr[i]);
    max_so_far = Math.max(curr_max, max_so_far);
  }
  return max_so_far;
}

console.log(maxSequence([-2, 1, -3, 4, -1, 2, 1, -5, 4])); // returns 6 : [4, -1, 2, 1]

/* If the solution specifically requires, that if the list is made up of only negative numbers or an empty list is given, zero should be returned - then few more lines can be added to explicitly take care of that. */

let allPositives = arr => arr.every(n => n > 0)
let allNegatives = arr => arr.every(n => n < 0)
let sum = arr => arr.reduce((curr_max, max_so_far) => curr_max + max_so_far, 0)

var maxSequence = function(arr){
  if(arr.length === 0 || allNegatives(arr)) return 0;
  if(allPositives(arr)) return sum(arr);

  var curr_max = 0, max_so_far = 0;

  for(var i = 0; i < arr.length; i++){  
    curr_max = Math.max(0, curr_max + arr[i]);
    max_so_far = Math.max(curr_max, max_so_far);
  }
  return max_so_far;
}

console.log(maxSequence([-2, -1, -3, -4, -1, -2, -1, -5, -4])); // returns 0
console.log(maxSequence([])); // returns 0
console.log(maxSequence([2, 1, 3, 4, 1, 2, 1, 5, 4])); // returns 23