Nodejs Utililty Methods Array Average

Array.prototype.avarage = function()
    return this.sum() / this.length;
Array.prototype.sum = function()
    var sum = 0;
    for(var i = this.length; -- i >= 0 ;)
        sum += (this[i] === null || this[i] === undefined) ? 0 : this[i];
    return sum;

Array.prototype.average = function() {
  var avg = 0;
  this.forEach(function(val) {
    avg += val;
  });
  return avg / this.length;
};

Array.prototype.average = function () {
  return this.sum() / this.length

Array.prototype.average = function(){
  return this.reduce( (a,b) => a + b, 0) / this.length

Array.prototype.average = function () {
  return this.sum() / this.length;
};
console.log([1, 2, 3, 4].average());

Array.prototype.average = function () {
  return (!this.length) ? NaN : this.reduce((acc, value) => {
    return acc + value;
  }) / this.length;
};

Array.prototype.average = function()
  if (this.length < 1) {
      return Number.NaN;
  return this.sum() / this.length;

Array.prototype.average = function () {
    var sum = 0, j = 0;
    for (var i = 0; i < this.length, isFinite(this[i]); i++) {
        sum += parseFloat(this[i]); ++j;
    return j ? sum / j : 0;
};

Array.prototype.average = function() {
  var sum = this.sum();
  var count = this.length;
  return sum/count;

Array.prototype.average = function(){
  var sum = 0;
  for (var i of this){
    sum += i;
  return sum / this.length;