Kata Array Helpers

array_helpers.js

/* jshint node: true */

var assert = require("chai").assert;

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


/*
 * square each item in array
 *
 * @return {Array}
 */

Array.prototype.square = function() {
  return this.map(function(n, i) {
    return n*n;
  });
};


/*
 * cube each item in array
 *
 * @return {Array}
 */

Array.prototype.cube = function() {
  return this.map(function(n, i) {
    return n*n*n;
  });
};


/*
 * add all items in array
 *
 * @return {Number}
 */

Array.prototype.sum = function() {
  return this.reduce(function(p, c) {
    return p + c;
  }, 0);
};


/*
 * averages all items in array
 *
 * @return {Number}
 */

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


/*
 * return only even numbers
 *
 * @return {Array}
 */

Array.prototype.even = function() {
  return this.filter(function(n, i) {
    return (n % 2) === 0;
  });
};


/*
 * return only odd numbers
 *
 * @return {Array}
 */

Array.prototype.odd = function() {
  return this.filter(function(n, i) {
    return (n % 2) !== 0;
  });
};


describe("array", function() {

  function assertDoesNotAffectOriginalArray() {
    it("does not affect the original array", function() {
      assert.deepEqual(numbers, origNumbers);
    });
  }

  describe("#square", function() {
    var squared;
    beforeEach(function() {
      squared = numbers.square();
    });

    it("squares each number in the array", function() {
      assert.deepEqual(squared, [1, 4, 9, 16, 25]);
    });

    assertDoesNotAffectOriginalArray();
  });

  describe("#cube", function() {
    var cubed;
    beforeEach(function() {
      cubed = numbers.cube();
    });

    it("cubes each number in the array", function() {
      assert.deepEqual(cubed, [1, 8, 27, 64, 125]);
    });

    assertDoesNotAffectOriginalArray();
  });

  describe("#sum", function() {
    it("adds all the items in the array", function() {
      assert.equal(numbers.sum(), 15);
    });
  });

  describe("#average", function() {
    it("averages all the items in the array", function() {
      assert.equal(numbers.average(), 3);
    });
  });

  describe("#even", function() {
    var evens;
    beforeEach(function() {
      evens = numbers.even();
    });

    it("returns only the even numbers", function() {
      assert.deepEqual(evens, [2, 4]);
    });

    assertDoesNotAffectOriginalArray();
  });

  describe("#odd", function() {
    var odds;
    beforeEach(function() {
      odds = numbers.odd();
    });

    it("returns only the odd numbers", function() {
      assert.deepEqual(odds, [1, 3, 5]);
    });

    assertDoesNotAffectOriginalArray();
  });
});