ArrayHelpers.js

// This kata is designed to test your ability to extend the functionality of built-in classes. In this case, we want you to extend the built-in Array class with the following methods: square(), cube(), average(), sum(), even() and odd().

// Explanation:

// square() must return a copy of the array, containing all values squared
// cube() must return a copy of the array, containing all values cubed
// average() must return the average of all array values; on an empty array must return NaN (note: the empty array is not tested in Ruby!)
// sum() must return the sum of all array values
// even() must return an array of all even numbers
// odd() must return an array of all odd numbers
// Note: the original array must not be changed in any case!

// Example
// var numbers = [1, 2, 3, 4, 5];

// numbers.square();  // must return [1, 4, 9, 16, 25]
// numbers.cube();    // must return [1, 8, 27, 64, 125]
// numbers.average(); // must return 3
// numbers.sum();     // must return 15
// numbers.even();    // must return [2, 4]
// numbers.odd();     // must return [1, 3, 5]


Array.prototype.square = function() {
  
  return this.map((el) => el**2)
   
}

Array.prototype.cube = function(){
  
  return this.map((el) => el * el * el)
}

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

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

Array.prototype.even = function(){
  
  return this.filter((el) => el % 2 === 0)
}

Array.prototype.odd = function(){
  
  return this.filter((el) => el % 2 === 1)
}

//different approach

Array.prototype.square  = function () { return this.map(function(n) { return n*n; }); }
Array.prototype.cube    = function () { return this.map(function(n) { return n*n*n; }); }
Array.prototype.average = function () { return this.sum() / this.length; }
Array.prototype.sum     = function () { return this.reduce(function(a, b) { return a + b; }, 0); }
Array.prototype.even    = function () { return this.filter(function(item) { return 0 == item % 2; }); }
Array.prototype.odd     = function () { return this.filter(function(item) { return 0 != item % 2; }); }

//different approach

Array.prototype.square = function() {
  var squared = [];
  for (var i = 0; i < this.length; i++) {
    squared[i] = Math.pow(this[i], 2);
  }
  return squared;
}

Array.prototype.cube = function() {
  var cubed = [];
  for (var i = 0; i < this.length; i++) {
    cubed[i] = Math.pow(this[i], 3);
  }
  return cubed;
}

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

Array.prototype.average = function() {
  if (this.length == 0) return NaN;
  return this.sum() / this.length;
}

Array.prototype.even = function() {
  var evens = [];
  for (var i = 0; i < this.length; i++) {
    if (this[i] % 2 == 0) evens.push(this[i]);
  }
  return evens;
}

Array.prototype.odd = function() {
  var odds = [];
  for (var i = 0; i < this.length; i++) {
    if (this[i] % 2 == 1) odds.push(this[i]);
  }
  return odds;
}