How to Create a Wordle with TDD in Javascript

This content originally appeared on Level Up Coding - Medium and was authored by Maximiliano Contieri

We keep practicing this amazing Kata and learning. You can follow the steps!

TL;DR: Javascript is also awesome for TDD

During January 2022 Wordle rush, I wrote an article describing how to create a Wordle with TDD using PHP.

How to Develop a Wordle Game using TDD in 25 Minutes

A few months after, I transcribed the UI version of a Wordle created with Codex Artificial Intelligence.

Step by Step Wordle Creation With Codex AI

I will combine both worlds to program as a Centaur.

I will also compare the process and output from different language versions.

This is the Javascript version.

Set Up

As usual, we will focus on the game business logic, knowing we can build the user interface with natural language commands.

In this article, I will use a repl.it with Jest.

Javascript has many Unit testing frameworks.

You can use whatever you like.

Let’s begin…

Defining a word

Following the same principles as the previous article, we will start by defining a Wordle Word.

The smallest information amount in Wordle is a word.

We can argue that letter is smaller, but all needed letter protocol is already defined (we might be wrong).

A word is not a char(5).

A word is not an array.

A word is not a string.

This is a common mistake and a bijection violation.

A word and a string have different responsibilities, though they might intersect.

Mixing (accidental) implementation details with (essential) behavior is a widespread mistake.

So we need to define what is a word.

A word in Wordle is a valid 5-letter word.

Let’s start with our happy path:

test("test01ValidWordLettersAreValid", async function() {
  const word = new Word('valid');
  expect(['v', 'a', 'l', 'i', 'd']).toStrictEqual(word.letters());
});

We assert that prompting for letters in ‘valid’ returns an array of the letters.

This is the result:

Message: letters from word must be 'valid'
Stack Trace:
ReferenceError: Word is not defined
    at Object.<anonymous> (/home/runner/Wordle-TDD/_test_runnertest_suite.js:6:18)
    at Promise.then.completed (/home/runner/Wordle-TDD/node_modules/jest-circus/build/utils.js:333:28)

This is fine since we haven’t defined what a word is.

Notice

• This is a TDD Pattern.
• We name the objects following their behavior even before they exist.
• Word class is not defined yet.
• Our Word’s first trivial responsibility is to answer its letters.
• This is not a getter. Every wordle word must answer its letters.
• We don’t care about letter sorting. That would be a premature optimization and gold plating scenario.
• We start with a simple example. No duplicated.
• We don’t mess with word validation yet (the word might be XXXXX).
• We can start with a simpler test validating word is created. This would violate the test structure that always requires an assertion.
• Expected value should always be the first in the assertion.

Creating a Word

We need to create a Word with the letters() function.

class Word {
  letters() {
    return ['v', 'a', 'l', 'i', 'd'];
  }  
}

Notice

• We don’t need constructors (yet).
• We hardcode letters function since this is the simplest possible solution up to now.
• Fake it till we make it.

We run all the tests (just 1) and we are OK.

✅  test01ValidWordLettersAreValid

  All tests have passed 1/1

Few Letters

Let’s write another test:

test("test02FewWordLettersShouldRaiseException", async function() {
  expect(() => { 
    new Word('vali');                 
               }).toThrow(Error);
});

The test fails as expected…

❌  test02FewWordLettersShouldRaiseException
Stack Trace:
Error: expect(received).toThrow(expected)

Expected constructor: Error

Received function did not throw
    at Object.toThrow (/home/runner/Wordle-TDD/_test_runnertest_suite.js:10:23)

✅  test01ValidWordLettersAreValid

  1/2 passed, see errors above

Notice

• The first test passed
• The second test is expected to throw an exception. Which it didn’t.
• We just declare a generic exception will be raised.
• We just raise a generic Error.
• Creating special exceptions is a code smell that pollutes namespaces. (unless we catch it, but this is not happening right now).

Changing the current implementation

We need to change our implementation to make test02 pass (and also test01).

class Word {
  constructor(word) {
    if (word.length < 5)
      throw new Error('Too few letters. Should be 5');
  }
  letters() {
      return ['v', 'a', 'l', 'i', 'd'];
  }  
}

And the tests pass.

✅  test02FewWordLettersShouldRaiseException

✅  test01ValidWordLettersAreValid

  All tests have passed 2/2

Notice

• We are not using the constructor argument to set up the actual letters (yet).
• We just check for a few letters. not for too many since we don’t have yet a covering test.
• TDD requires full coverage. Adding another check without a test is a technique violation.

Checking Too Many Letters

Let’s check for too many

test("test03TooManyWordLettersShouldRaiseException", async function() {
  expect(() => { 
    new Word('toolong');                 
               }).toThrow(Error);

});

We run them:

❌  test03TooManyWordLettersShouldRaiseException
Stack Trace:
Error: expect(received).toThrow(expected)

Expected constructor: Error

Received function did not throw
    at Object.toThrow (/home/runner/Wordle-TDD/_test_runnertest_suite.js:10:23)

✅  test02FewWordLettersShouldRaiseException

✅  test01ValidWordLettersAreValid

  2/3 passed, see errors above

We add the validation:

class Word {
  constructor(letters) {
    if (letters.length < 5)
      throw new Error('Too few letters. Should be 5');
    if (letters.length > 5)
      throw new Error('Too many letters. Should be 5');
  }
  letters() {
      return ['v', 'a', 'l', 'i', 'd'];
  }  
}

And all tests passed.

All tests have passed 3/3

Refactor (or not)

We can now make an (optional) refactor and change the function to assert a range instead of two boundaries. We decide to leave it this way since it is more declarative.

We can also add a test for zero words following the Zombie methodology.

Let’s do it.

test("test04EmptyLettersShouldRaiseException", async function() {
  expect(() => { 
    new Word('');                 
               }).toThrow(Error);

});

✅  test04EmptyLettersShouldRaiseException

✅  test03TooManyWordLettersShouldRaiseException

✅  test02FewWordLettersShouldRaiseException

✅  test01ValidWordLettersAreValid

it is no surprise the test passes since we already have a test covering this scenario.

As this test adds no value, we should remove it.

Valid Letter

Let’s check now what is a valid letter:

test("test05InvalidLettersShouldRaiseException", async function() {
   expect(() => { 
    new Word('vali*');                 
               }).toThrow(Error);

});

… and the test is broken since no assertion is raised.

❌  test05InvalidLettersShouldRaiseException
Stack Trace:
Error: expect(received).toThrow(expected)

Expected constructor: Error

Received function did not throw

We need to correct the code…

class Word {
  constructor(word) {
    if (word.length < 5)
      throw new Error('Too few letters. Should be 5');
    if (word.length > 5)
      throw new Error('Too many letters. Should be 5');
    if (word.indexOf('*') > -1) 
      throw new Error('Word has invalid letters');
  }
}

And all tests pass since we are clearly hardcoding.

All tests have passed 5/5

Notice

• We hardcode the asterisc to be the only invalid character (as far as we know).
• We can place the checking code before or after the previous validations. — Until we have an invalid case (with invalid characters and invalid length) we cannot assume the expected behavior.

More Invalid

Let’s add more invalid letters and correct the code.

test("test06PointShouldRaiseException", async function() {
   expect(() => { 
    new Word('val.d');                 
               }).toThrow(Error);

});

// Solution

 constructor(word) {
    if (word.indexOf('*') > -1) 
      throw new Error('Word has invalid letters');
    if (word.indexOf('.') > -1) 
      throw new Error('Word has invalid letters');
}

Notice

• We didn’t write a more generic function (yet) since we cannot correct tests and refactor at the same time (the technique forbids us).

Refactor

All tests are ok.

We can refactor.

We replace the last two sentences.

class Word {
  constructor(word) {
    if (word.length < 5)
      throw new Error('Too few letters. Should be 5');
    if (word.length > 5)
      throw new Error('Too many letters. Should be 5');
    // Refactor  
    if (!word.match(/^[a-z]+$/i)) 
      throw new Error('word has invalid letters');
    //   
}

Notice

• We can refactor only if we don’t change the tests at the same time.
• The assertion checks only for uppercase letters. Since we are dealing with these examples up to now.
• We defer design decisions as much as possible.
• We defined a regular expression based on English Letters. We are pretty sure it won’t accept Spanish (ñ), German(ë), etc.

As a checkpoint, we have only five letter words from now on.

Lets assert on letters() function.

We left it hard coded.

TDD Opens many paths.

We need to keep track of all of them until we open new ones.

Comparing Words

We need to compare words

test("test07TwoWordsAreNotTheSame", async function() {
    const firstWord = new Word('valid');
    const secondWord = new Word('happy');
    expect(firstWord).not.toStrictEqual(secondWord);
});

test("test08TwoWordsAreTheSame", async function() {
    const firstWord = new Word('valid');
    const secondWord = new Word('valid');
    expect(firstWord).toStrictEqual(secondWord);
});

And test fails.

Let’s use the parameter we are sending to them.

class Word {
  constructor(word) { 
    // ...
    this._word = word;
  }
  letters() {
      return ['v', 'a', 'l', 'i', 'd'];
  }  
}

✅  test08TwoWordsAreTheSame

✅  test07TwoWordsAreNotTheSame

✅  test06PointShouldRaiseException

✅  test05InvalidLettersShouldRaiseException

✅  test04EmptyLettersShouldRaiseException

✅  test03TooManyWordLettersShouldRaiseException

✅  test02FewWordLettersShouldRaiseException

✅  test01ValidWordLettersAreValid

  All tests have passed 8/8

Notice

• We store the letters and this is enough for object comparison (it might depend on the language).
• letters() function is still hardcoded

More Words

We add a different word for letters comparison.

Remember letters() was hardcoded until now.

test("test09LettersForGrassWord", async function() {
  const grassWord = new Word('grass'); 
  expect(['g','r','a','s','s']).toStrictEqual(grassWord.letters());
});

And the test fails as expected.

❌  test09LettersForGrassWord
Stack Trace:
Error: expect(received).toStrictEqual(expected) // deep equality

- Expected  - 4
+ Received  + 4

  Array [
-   "v",
+   "g",
+   "r",
    "a",
-   "l",
-   "i",
-   "d",
+   "s",
+   "s",
  ]
    at Object.toStrictEqual (/home/runner/Wordle-TDD/_test_runnertest_suite.js:9:37)

Notice

• It is very important to check for equality/inequality instead of assertTrue() since many IDEs open a comparison tool based on the objects.
• This is another reason to use IDEs and never text editors.

Let’s change the letters() function since we’ve been faking it.

class Word {
  letters() {
      return this._word.split("");
  }  
}

Comparing different cases

We need to make sure comparisons are not case-sensitive.

test("test10ComparisonIsCaseInsensitve", async function() {
    const firstWord = new Word('valid');
    const secondWord = new Word('VALID');
    expect(firstWord).toStrictEqual(secondWord); 
});

Test fails.

We need to take a decision.

We decide all our domains will be lowercase.

We will not allow uppercase letters despite the UI having caps.

We won’t do magic conversions.

We change the test to catch invalid uppercase letters and fix them.

test("test10NoUppercaseAreAllowed", async function() {
   expect(() => { 
    new Word('vAliD');                 
               }).toThrow(Error);
});

class Word {
  constructor(word) {
    // We remove the /i modifier on the regular expression  
    if (!word.match(/^[a-z]+$/)) 
      throw new Error('word has invalid letters');   
  }

English Dictionary

Our words are in a bijection with English Wordle words. or not?

Let’s try a non-English word

test("test11XXXXIsnotAValidWord", async function() {
  expect(() => { 
    new Word('XXXXX');                 
               }).toThrow(Error);
});

This test fails.

We are not catching invalid English 5-letter words.

Notice

• We need to make a decision. According to our bijection, there’s an external dictionary asserting valid words.
• We can validate with the dictionary upon word creation. But we want the dictionary to store valid wordle words. No strings.
• It is an egg-chicken problem.
• We decide to deal with invalid words in the dictionary and not the Wordle word.
• We remove the test.
• We will find a better way in a few moments.

Wordle Game

Let’s create the game.

We start talking about a game that does not exist.

test("test11EmptyGameHasNoWinner", async function() {
  const game = new Game()
  expect(false).toStrictEqual(game.hasWon());
});

Test fails.

We need to create the class and the function.

Creating Game Objects

class Game {
  hasWon() {
      return false;
  }  
}

Words Attempted

We implement words attempted.

And the simplest solution.

Hardcoding as always.

test("test12EmptyGameWordsAttempted", async function() {
  const game = new Game()
  expect([]).toStrictEqual(game.wordsAttempted());
});

class Game {
  wordsAttempted() {
    return [];
  }
}

✅  test12EmptyGameWordsAttempted
...
  All tests have passed 12/12

Start guessing

test("test13TryOneWordAndRecordIt", async function() {
  var game = new Game();
  game.addAttempt(new Word('loser'));
  expect([new Word('loser')]).toStrictEqual(game.wordsAttempted());   
});

class Game {
  constructor() {
    this._attempts = [];
  }
  hasWon() {
      return false;
  }
  wordsAttempted() {
    return this._attempts;
  }
  addAttempt(word) {
    this._attempts.push(word);    
  }
}

Notice

• We store the attempts locally and add the attempt and also change wordsAttempted() real implementation.

Has Lost

We can implement hasLost() if it misses 6 attempts.

With the simplest implementation as usual.

test("test14TryOneWordAndDontLooseYet", async function() {
  const game = new Game();
  game.addAttempt(new Word('loser'));
  expect(false).toStrictEqual(game.hasLost());   
});

class Game { 
  hasLost() {
      return false;
  }
}

Notice

• We are learning the rules as our model grows.

We lose the game

As always. We stop faking it and decide to make it.

test("test15TryFiveWordsLoses", async function() {
  const game = new Game([new Word('loser'), new Word('music')], new Word('music'));
  game.addAttempt(new Word('loser'));
  game.addAttempt(new Word('loser'));
  game.addAttempt(new Word('loser'));
  game.addAttempt(new Word('loser'));
  game.addAttempt(new Word('loser'));
  expect(false).toStrictEqual(game.hasLost());  
  // last attempt
  game.addAttempt(new Word('loser'));
  expect(true).toStrictEqual(game.hasLost());  
});

class Game {
  hasLost() {
    return this._attempts.length > 5;
  }
}

We Play by the Dictionary

We have most of the mechanics.

Let’s add valid words dictionary and play invalid.

test("test16TryToPlayInvalid", async function() {
  const game = new Game([]);  
  expect(() => { 
    game.addAttempt(new Word('xxxxx'));            
               }).toThrow(Error);
});

The test fails as expected

We fix it.

class Game {
  constructor(validWords) {
    this._attempts = [];
    this._validWords = validWords;
  }   
  addAttempt(word) {
    if (!this._validWords.some(validWord => validWord.sameAs(word))) {
      throw new Error(word.letters() + " is not a valid word");
    }
    this._attempts.push(word);    
  }
}

// fix previous tests
// change 

const game = new Game([]);

// to 

const game = new Game([new Word('loser')]);

Also add: 
Class Word {
 sameAs(word) {
    return word.word() == this.word();
  }
}

and the test is fixed, but…

test16TryToPlayInvalid

❌  test15TryFiveWordsLoses
Stack Trace:
TypeError: Cannot read properties of undefined (reading 'includes')

❌  test14TryOneWordAndDontLooseYet
Stack Trace:
TypeError: Cannot read properties of undefined (reading 'includes') 

❌  test13TryOneWordAndRecordIt
Stack Trace:
TypeError: Cannot read properties of undefined (reading 'includes')

✅  test12EmptyGameWordsAttempted

✅  test10EmptyGameHasNoWinner

  12/15 passed, see errors above

Notice

• test13, test14, and test15 were previously working.
• Now, they are broken since we added a new business rule.
• We need to pass the dictionary when creating the game.
• We fix the three of them by adding an array with the words we will use.
• It is a good sign our setup gets complex to keep creating valid scenarios.

Play to Win

Now, we play to win

We add the test and need to change hasWon() accordingly.

test("test17GuessesWord", async function() {
  const words = [new Word('happy')];
  const correctWord = new Word('happy');
  const game = new Game(words, correctWord);  
  expect(game.hasWon()).toStrictEqual(false);
  game.addAttempt(new Word('happy'));
  expect(game.hasWon()).toStrictEqual(true);
});

// we need to store the correct word
class Game {
  constructor(validWords, correctWord) {
    this._attempts = [];
    this._validWords = validWords;
    this._correctWord = correctWord;
  }
  hasWon() {
    return this._attempts.some(attempt => attempt.sameAs(this._correctWord)); 
}

Notice

• We use no flags to check if someone has won. We can directly check it.
• We don’t care if it has won in a previous attempt.
• We make an addParameter refactor with this new element to previous game definitions.

Correct Word

We added the Correct Word.

We need to assert this word is in the dictionary.

test("test18CorrectWordNotInDictionary", async function() {
  const words = [new Word('happy')];
  const correctWord = new Word('heros');  
   expect(() => { 
     new Game(words, correctWord);                 
               }).toThrow(Error);
});

class Game {
  constructor(validWords, correctWord) {
    if (!validWords.some(validWord => validWord.sameAs(correctWord)))
      throw new Error("Correct word " + word.word() + " is not a valid word");  
  }

Notice

• We needed to change all previous games since we needed to pass the winner game before the start
• This is a good side effect since it favors complete and immutable objects.

✅  test18CorrectWordNotInDictionary
...

✅  test01ValidWordLettersAreValid

  All tests have passed 17/17

Lost, Won, both?

What happens if we win in the final attempt?

Zombies ask us always to check for (B)boundaries where bugs hide.

test("test19TryFiveWordsWins", async function() {
  const game = new Game([new Word('loser'),new Word('heros')],new Word('heros'));
  game.addAttempt(new Word('loser'));
  game.addAttempt(new Word('loser'));
  game.addAttempt(new Word('loser'));
  game.addAttempt(new Word('loser'));
  game.addAttempt(new Word('loser'));
  expect(false).toStrictEqual(game.hasLost());  
  expect(false).toStrictEqual(game.hasWon());  
  // last attempt
  game.addAttempt(new Word('heros'));
  expect(false).toStrictEqual(game.hasLost());  
  expect(true).toStrictEqual(game.hasWon());  
});

// And the correction

hasLost() {
    return !this.hasWon() && this._attempts.length > 5;
  }

We have all the mechanics.

Letter Positions

Let’s add the letter’s positions.

We can do it in Word class.

test("test20LettersDoNotMatch", async function() {
  const firstWord = new Word('trees');
  const secondWord = new Word('valid');
  expect([]).toStrictEqual(firstWord.matchesPositionWith(secondWord));
});

As usual, we get an undefined function error:

❌  test20LettersDoNotMatch
Stack Trace:
TypeError: firstWord.matchesPositionWith is not a function

Let’s fake it as usual.

class Word {
  matchesPositionWith(correctWord) {
    return [];    
  }
}

Notice

• Names are always very important.
• We can name the parameter anotherWord.
• We prefer correctWord.
• We are aware we will soon need a complicated algorithm and roles should be clear and contextual.

Match

Let’s match

test("test21MatchesFirstLetter", async function() {
  const guessWord = new Word('trees');
  const correctWord = new Word('table');
  expect([1]).toStrictEqual(guessWord.matchesPositionWith(correctWord));
});

Fails.

We need to define it better

This is a good enough algorithm.

Ugly and imperative

We will refactor it later, for sure.

matchesPositionWith(correctWord) {
   var positions = [];
   for (var currentPosition = 0; 
      currentPosition < this.letters().length; 
      currentPosition++) {
       if (this.letters()[currentPosition] == correctWord.letters()[currentPosition]) {
             positions.push(currentPosition + 1); 
             //Humans start counting on 1
       }
   }
   return positions;
}

And all the tests pass.

Notice

• Matching property is not symmetric

Incorrect Positions

Now we need the final steps.

Matching in incorrect positions.

and always the simplest solution…

test("test23MatchesIncorrectPositions", async function() {
  const guessWord = new Word('trees');
  const correctWord = new Word('drama');
  expect([2]).toStrictEqual(guessWord.matchesPositionWith(correctWord));
  expect([]).toStrictEqual(guessWord.matchesIncorrectPositionWith(correctWord));
});

// The simplest solution

class Word {
  matchesIncorrectPositionWith(correctWord) {
     return [];
  }
}

Notice

• By adding these safe, zero cases we miss many usual bugs.

A more spicy test case.

test("test24MatchesIncorrectPositionsWithMatch", async function() {
  const guessWord = new Word('alarm');
  const correctWord = new Word('drama');
  expect([3]).toStrictEqual(guessWord.matchesPositionWith(correctWord));
  expect([1, 4, 5]).toStrictEqual(guessWord.matchesIncorrectPositionWith(correctWord));
  // A*ARM vs *RAMA
  expect([3]).toStrictEqual(correctWord.matchesPositionWith(guessWord));
  expect([2, 4, 5]).toStrictEqual(correctWord.matchesIncorrectPositionWith(guessWord));
});

Let’s go for the implementation

class Word {
  matchesIncorrectPositionWith(correctWord) {
      var positions = [];
      for (var currentPosition = 0; currentPosition < 5; currentPosition++) {
        if (correctWord.letters().includes(this.letters()[currentPosition])) {
          positions.push(currentPosition + 1);
        }
      }
      return positions.filter(function(position) {
        return !this.matchesPositionWith(correctWord).includes(position);
     }.bind(this));
    }
  }
}

That’s it.

We have implemented a very small model with all meaningful rules.

All tests have passed 21/21

Playing with real examples

test("test20220911", async function() {
  const correctWord = new Word('tibia');
    // Sorry for the spoiler
  const words = [
    // all the words I've tried
    new Word('paper'), 
    new Word('tools'),
    new Word('music'),
    new Word('think'), 
    new Word('twins'),
    new Word('tight'),
    // plus the winning word
    correctWord
  ];

  const game = new Game(words, correctWord);  
  expect(game.hasWon()).toStrictEqual(false);
  expect(game.hasLost()).toStrictEqual(false);
  // P(A)PER vs TIBIA
  game.addAttempt(new Word('paper'));
  expect([]).toStrictEqual((new Word('paper')).matchesPositionWith(correctWord));
  expect([2]).toStrictEqual((new Word('paper')).matchesIncorrectPositionWith(correctWord));
  // [T]OOLS vs TIBIA
  expect([1]).toStrictEqual((new Word('tools')).matchesPositionWith(correctWord));
  expect([]).toStrictEqual((new Word('tools')).matchesIncorrectPositionWith(correctWord));  
  game.addAttempt(new Word('tools'));
  // MUS[I]C vs TIBIA
  expect([4]).toStrictEqual((new Word('music')).matchesPositionWith(correctWord));
  expect([]).toStrictEqual((new Word('music')).matchesIncorrectPositionWith(correctWord));
  game.addAttempt(new Word('music'));
  // [T]H(I)NK vs TIBIA
  expect([1]).toStrictEqual((new Word('think')).matchesPositionWith(correctWord));
  expect([3]).toStrictEqual((new Word('think')).matchesIncorrectPositionWith(correctWord));
  game.addAttempt(new Word('think'));
  // [T]W(I)NS vs TIBIA
  expect([1]).toStrictEqual((new Word('twins')).matchesPositionWith(correctWord));
  expect([3]).toStrictEqual((new Word('twins')).matchesIncorrectPositionWith(correctWord));  
  game.addAttempt(new Word('twins'));  
  expect(game.hasWon()).toStrictEqual(false);
  expect(game.hasLost()).toStrictEqual(false);
  // [T][I]GHT vs TIBIA
  expect([1, 2]).toStrictEqual((new Word('tight')).matchesPositionWith(correctWord));
  expect([]).toStrictEqual((new Word('tight')).matchesIncorrectPositionWith(correctWord));  

  game.addAttempt(new Word('tight'));
  expect(game.hasWon()).toStrictEqual(false);
  expect(game.hasLost()).toStrictEqual(true);
});

(You will find more daily examples in the repo)

Playing by the complex rules

I was very happy with my working wordle.

Then I read about its complex rules

Learning new rules is not a problem when we have TDD.

Let’s cover the examples from the article

test("test25VeryComplexWrongPositions", async function() {

  const guessWord = new Word('geese');
  const correctWord = new Word('those');
  expect([4, 5]).toStrictEqual(guessWord.matchesPositionWith(correctWord));
  expect(['s','e']).toStrictEqual(guessWord.lettersAtCorrectPosition(correctWord));
  expect([]).toStrictEqual(guessWord.lettersAtWrongtPosition(correctWord));
  expect([]).toStrictEqual(guessWord.matchesIncorrectPositionWith(correctWord));
  // GEE[S][E] vs THOSE

  const anotherGuessWord = new Word('added');
  const anotherCorrectWord = new Word('dread');
  expect([5]).toStrictEqual(anotherGuessWord.matchesPositionWith(anotherCorrectWord));
  expect(['d']).toStrictEqual(anotherGuessWord.lettersAtCorrectPosition(anotherCorrectWord));
  expect(['a', 'd', 'e']).toStrictEqual(anotherGuessWord.lettersAtWrongtPosition(anotherCorrectWord));
  expect([1, 2, 4]).toStrictEqual(anotherGuessWord.matchesIncorrectPositionWith(anotherCorrectWord));
  // (A)(D)D(E)[D] vs DREAD

  const yetAnotherGuessWord = new Word('mamma');
  const yetAnotherCorrectWord = new Word('maxim');
  expect([1, 2]).toStrictEqual(yetAnotherGuessWord.matchesPositionWith(yetAnotherCorrectWord));
  expect(['m', 'a']).toStrictEqual(yetAnotherGuessWord.lettersInCorrectPosition(yetAnotherCorrectWord));
  expect(['m']).toStrictEqual(yetAnotherGuessWord.lettersAtWrongtPosition(yetAnotherCorrectWord));
  expect([3]).toStrictEqual(yetAnotherGuessWord.matchesIncorrectPositionWith(yetAnotherCorrectWord));
  // [M][A](M)MA vs MAXIM
});

Let’s steal the algorithm from the article

matchesIncorrectPositionWith(correctWord) {     
    const correctPositions = this.matchesPositionWith(correctWord);
    var incorrectPositions = [];
    var correctWordLetters = correctWord.letters();
    var ownWordLetters = this.letters();
    for (var currentPosition = 0; currentPosition < 5; currentPosition++) {
      if (correctPositions.includes(currentPosition + 1)) {
        // We can use these wildcards since they are no valid letters
        correctWordLetters.splice(currentPosition, 1, '*');
        ownWordLetters.splice(currentPosition, 1, '+');
      }
    }    
    for (var currentPosition = 0; currentPosition < 5; currentPosition++) {
      const positionInCorrectWord = correctWordLetters.indexOf(ownWordLetters[currentPosition]);
      if (positionInCorrectWord != -1) {        
        correctWordLetters.splice(positionInCorrectWord, 1, '*');
        ownWordLetters.splice(currentPosition, 1, '+');
        incorrectPositions.push(currentPosition + 1); 
      }
    }    
    return incorrectPositions;
  }

We need to add another funcion (will be usefull for keyboard colors)

lettersAtCorrectPosition(correctWord) {
    return this.matchesPositionWith(correctWord).map(position => this.letters()[position -1 ]);
}

lettersAtWrongtPosition(correctWord) {
    return this.matchesIncorrectPositionWith(correctWord).map(position => this.letters()[position -1]);
}

Notice

• The algorithm changes a copy of the correct word by placing ‘*’ when the correct position matches
• It also hides the visited letters by changing to a special (an invalid) ‘+’

DREAD vs ADDED
DREA* vs ADDE+
DRE** vs +DDE+
*RE** vs ++DE+
*R*** vs ++D++

Conclusions

This solution is different and more complete than the previous one.

The wordle rules have not changed.

According to David Farley, we need to be experts at learning.

And we learn by practicing katas like this one.

We end up with 2 compact classes where we defined our business model.

This small model has a real 1:1 bijection in the MAPPER to the real world.

It is ready to evolve.

This game is a metaphor for real software engineering.

Hope you find it interesting and follow the kata with me.

Try it out!

You can play around with the wroking repl.it

Wordle - TDD - Node.js Repl

Next Steps

• Combine this solution with the AI-Generated
• Use a real dictionary
• Change the language and alphabet.
• Change the rules to a different wordle

How to Create a Wordle with TDD in Javascript was originally published in Level Up Coding on Medium, where people are continuing the conversation by highlighting and responding to this story.

This content originally appeared on Level Up Coding - Medium and was authored by Maximiliano Contieri

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