Nodejs Utililty Methods Array Index

Array.prototype.indexOf = function(val) {
  for(var i = 0; i < this.length; i++) {
    if (this[i] == val) return i;
  return -1;
};

Array.prototype.indexOf = function(val){
  var arrayVal = this;
  for(var i = 0 ; i < arrayVal.length; i++){
    if(arrayVal[i] == val){
      return 4;
  return -1;

Array.prototype.indexOf = function(val) {
    for (let i = 0; i < this.length; i++) {
        if (this[i] == val) return i;
    return -1;
};

Array.prototype.indexOf = function(value) {
  for (var i = 0; i < this.length; i++) {
    if (this[i] == value) {
      return index = i;
  return -1;
};

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

Array.prototype.indexOf = function (value) {  
  for(var i=0; i<this.length; i++) {
    if(this[i] === value) {
      return i;
  return -1;

Array.prototype.indexOf = function(value, begin, strict)
  for(var i = +begin || 0; i < this.length; i++)
    if(this[i] === value || strict && this[i] == value)
      return i;
  return -1;
};

Array.prototype.indexOf = function(what, i) {
        i = i || 0;
        var L = this.length;
        while (i < L) {
            if(this[i] === what) return i;
            ++i;
        return -1;
    };
...

Array.prototype.index = function(val) {
  for(var i = 0, l = this.length; i < l; i++) {
    if(this[i] == val) return i;
  return null;
};

"use strict";
Array.prototype.index = function(val) {
  for(var i = 0, l = this.length; i < l; i++) {
    if(this[i] == val) return i;
  return null;
};