Nodejs Utililty Methods Array Find

Array.prototype.findFirst = function (test) {
    var i, item;
    for (i = 0; i < this.length; i++) {
  item = this[i];
  if (test(item)) {
      return item;
};
...

Array.prototype.findHighestNumber = function(inField)
  var tmp = [];
  for (var i = 0; i < this.length; i++) {
    tmp[i] = Number(this[i][inField]);
  if(this.length < 1)
    return 0;
  return Math.max.apply(Math, tmp);
...

Array.prototype.findIdx = function(fn) {
    return this.indexOf(this.filter(val => fn(val))[0]);
};

Array.prototype.findIfNotError = function(filter) {
    var result = this.find(filter);
    if ( !result ) {
        throw new Error();
    return result;

Array.prototype.findInJson = function (attr, value){
  for(var i=0; i<this.length; i++){
    this[i][attr] = this[i][attr].toLowerCase();
    if(this[i][attr] == value){
      return true;
    };
  };
  return false;
};
...

var array = [47, 98, 0, -23, 4, 87.3, 0.0003, +9];
Array.prototype.findMaximum = function findIt() {
var arrayValue = 0;
for(var i = 0; i < array.length; i++) {
  if (array[i] > arrayValue) {
    arrayValue = array[i];
  return arrayValue;
...

Array.prototype.findRanges = function() {
  var buckets = {};
  for(var i = 0; i < this.length; i++) {
    if(!(this[i] in buckets)) {
      buckets[this[i]] = [{
        from: i,
        to: i
      }]
    } else {
...

Array.prototype.findThing = function(n){
  for(var i=0; i<this.length; i++){
    if(this[i] === n){
      return true;
    };
  };
  return false;
};

Array.prototype.findYoungestPerson = function findYoungestPerson() {
        var youngest = this[0];
    for (var person = 1; person < this.length; person += 1) {
        if (this[person].age < youngest.age) {
            youngest = this[person];
    return youngest;
};
...

Array.prototype.find_by = function(prop, val) {
  return this.filter(function(obj) {
    return obj[prop] === val
  }).first()