Nodejs Utililty Methods Array Sum

Array.prototype.sum = function() {
  if (this.length === 0) {
    return 0;
  } else if (this.length === 1) {
    return parseInt(this[0], 10);
  } else {
    return this.reduce(function(x, y) {
      return x + y;
    });
...

Array.prototype.sum = function(){
  for(var i=0,sum=0;i<this.length;i++) {
    var val = Number(this[i]);
    if (!isNaN(val)) {
      sum += val;
  return sum;
};
...

Array.prototype.sum = function() {
  var result = 0;
  for (var i = 0; i < this.length; i++) result += this[i];
  return result;

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

Array.prototype.sum = function() {
  var sum = 0;
  for (var i = 0; i < this.length; i++) {
    if (!isNaN(Number(this[i]))) {
      sum += Number(this[i]);
  return sum;
};
...

Array.prototype.sum = function(){
  return this.reduce((acc,x) => acc + x);

Array.prototype.sum = function() {
  return this.isEmpty() ? 0 : this.reduce( (a, b) => { return a + b} );
};

Array.prototype.sum = function() {
  for ( var a = 0, c = this.length, b = 0; a < c; b += this[a++]) {
  return b
};

Array.prototype.sum = function(array) { 
    return this.reduce(function(a,b) { 
        return a + b 
    }) 

Array.prototype.sum = function(begin, end) {
  var total = 0;
  for (var i = begin >> 0 || 0, len = end + 1 >> 0 || this.length >> 0; i < len; i++) {
    total += +this[i] || 0;
  return total;
};