JS | Vikings Object Oriented Programming

Introduction

We have learned Object Oriented Programming and Prototypal inheritance with JavaScript. Now we will work with our Viking friends applying all the concepts we just learned today. Let's start with the exercise.

Requirements

• Fork this repo
• Clone this repo into your ~/code/labs
• Make sure you use objects and prototypal inheritance during the exercise.
• We should follow good object oriented principals.

Submission

• Upon completion, run the following commands

git add .
git commit -m "done"
git push origin master

• Navigate to your repo and create a Pull Request

Tests, test, tests!

Yes! Best way to know how our code is doing is to work with tests. Go ahead and open the SpecRunner.html!

Run the tests

We've got a test suite for our constructor functions and their methods but there are no tests currently being executed. We have to uncomment each it() inside of tests/VikingSpec.js and implement the code in src/viking.js to make each test pass.

If you open tests/VikingSpec.js and take a look at lines 10-20. You should see some it() functions (tests) that are commented out. Let's start by uncommenting lines 10-12:

  describe("constructor function", function () {
    it("should receive 2 arguments (health & strength)", function () {
      expect(Soldier.length).toEqual(2);
    });

    // it("should receive the health property as its 1st argument", function () {
    //   expect(soldier.health).toEqual(health);
    // });

    // it("should receive the strength property as its 2nd argument", function () {
    //   expect(soldier.strength).toEqual(strength);
    // });
  });

Now that particular test (should receive 2 arguments (health & strength)) is failing!

Write the code

Now we have to write the correct code in the src/viking.js file to make the test pass. The starter code you will find in the file is the following:

// Soldier
class Soldier {}

// Viking
class Viking {}

// Saxon
class Saxon {}

// War
class War {}

In this case, the test says that Soldier constructor function should receive 2 arguments (health & strength), so we have to write the correct code that passes this test. Let's make the Soldier constructor function receive two arguments:

// Soldier
class Soldier {
  constructor(healthArg, strengthArg) {}
}

// Viking
class Viking {}

// Saxon
class Saxon {}

// War
class War {}

Execute all the tests

Now that we are passing the first test, the next step is to uncomment the next test. To do that, we have to remove the comments from lines 15-17 in the spec/VikingSpec.js file, and refresh the page to see what we have to implement next:

Once we have checked out that the test is failing, we can implement the code to make it pass.

Exercise

---

Soldier

Modify the Soldier constructor function and add 2 methods to its prototype: attack(), and receiveDamage().

constructor function

• should receive 2 arguments (health & strength)
• should receive the health property as its 1st argument
• should receive the strength property as its 2nd argument

attack() method

• should be a function
• should receive 0 arguments
• should return the strength property of the Soldier

receiveDamage() method

• should be a function
• should receive 1 argument (the damage)
• should remove the received damage from the health property
• shouldn't return anything

---

Viking

A Viking is a Soldier with an additional property, their name. They also have a different receiveDamage() method and new method, battleCry().

Modify the Viking constructor function, have it inherit from Soldier, reimplement the receiveDamage() method for Viking, and add a new battleCry() method.

inheritance

• Viking should inherit from Soldier

constructor function

• should receive 3 arguments (name, health & strength)
• should receive the name property as its 1st argument
• should receive the health property as its 2nd argument
• should receive the strength property as its 3rd argument

attack() method

(This method should be inherited from Soldier, no need to reimplement it.)

• should be a function
• should receive 0 arguments
• should return the strength property of the Viking

receiveDamage() method

(This method needs to be reimplemented for Viking because the Viking version needs to have different return values.)

• should be a function
• should receive 1 argument (the damage)
• should remove the received damage from the health property
• if the Viking is still alive, it should return "NAME has received DAMAGE points of damage"
• if the Viking dies, it should return "NAME has died in act of combat"

battleCry() method

Learn more about battle cries.

• should be a function
• should receive 0 arguments
• should return "Odin Owns You All!"

---

Saxon

A Saxon is a weaker kind of Soldier. Unlike a Viking, a Saxon has no name. Their receiveDamage() method will also be different than the original Soldier version.

Modify the Saxon, constructor function, have it inherit from Soldier and reimplement the receiveDamage() method for Saxon.

inheritance

• Saxon should inherit from Soldier

constructor function

• should receive 2 arguments (health & strength)
• should receive the health property as its 1st argument
• should receive the strength property as its 2nd argument

attack() method

(This method should be inherited from Soldier, no need to reimplement it.)

• should be a function
• should receive 0 arguments
• should return the strength property of the Saxon

receiveDamage() method

(This method needs to be reimplemented for Saxon because the Saxon version needs to have different return values.)

• should be a function
• should receive 1 argument (the damage)
• should remove the received damage from the health property
• if the Saxon is still alive, it should return "A Saxon has received DAMAGE points of damage"
• if the Saxon dies, it should return "A Saxon has died in combat"

---

(BONUS) War

Now we get to the good stuff: WAR! Our War constructor function will allow us to have a Viking army and a Saxon army that battle each other.

Modify the War constructor and add 5 methods to its prototype:

• addViking()
• addSaxon()
• vikingAttack()
• saxonAttack()
• showStatus()

constructor function

When we first create a War, the armies should be empty. We will add soldiers to the armies later.

• should receive 0 arguments
• should assign an empty array to the vikingArmy property
• should assign an empty array to the saxonArmy property

addViking() method

Adds 1 Viking to the vikingArmy. If you want a 10 Viking army, you need to call this 10 times.

• should be a function
• should receive 1 argument (a Viking object)
• should add the received Viking to the army
• shouldn't return anything

addSaxon() method

The Saxon version of addViking().

• should be a function
• should receive 1 argument (a Saxon object)
• should add the received Saxon to the army
• shouldn't return anything

vikingAttack() method

A Saxon (chosen at random) has their receiveDamage() method called with the damage equal to the strength of a Viking (also chosen at random). This should only perform a single attack and the Saxon doesn't get to attack back.

• should be a function
• should receive 0 arguments
• should make a Saxon receiveDamage() equal to the strength of a Viking
• should remove dead saxons from the army
• should return result of calling receiveDamage() of a Saxon with the strength of a Viking

saxonAttack() method

The Saxon version of vikingAttack(). A Viking receives the damage equal to the strength of a Saxon.

• should be a function
• should receive 0 arguments
• should make a Viking receiveDamage() equal to the strength of a Saxon
• should remove dead vikings from the army
• should return result of calling receiveDamage() of a Viking with the strength of a Saxon

showStatus() method

Returns the current status of the War based on the size of the armies.

• should be a function
• should receive 0 arguments
• if the Saxon array is empty, should return "Vikings have won the war of the century!"
• if the Viking array is empty, should return "Saxons have fought for their lives and survive another day..."
• if there are at least 1 Viking and 1 Saxon, should return "Vikings and Saxons are still in the thick of battle."

---

//Happy Coding!!