flag-guessing-game/index.html at main · sitepoint-editors/flag-guessing-game · GitHub

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<!DOCTYPE html>
<html lang="en" data-theme="light">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<meta name="color-scheme" content="light">
<title>Tutorial</title>

<link rel="icon" href="data:image/svg+xml,<svg xmlns=%22http://www.w3.org/2000/svg%22 viewBox=%220 0 100 100%22><text y=%22.9em%22 font-size=%2290%22> 🏳️</text></svg>">

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<link
  rel="stylesheet"
  href="https://cdn.jsdelivr.net/npm/@picocss/pico@2/css/pico.min.css"
>

<style>
    .container { max-width: 800px; }
    section { margin-bottom: 3rem; border-bottom: 1px solid rgba(0,0,0,0.2); padding-bottom: 2rem; }
    h1 { text-align: center; margin: 2rem 0 3rem 0; }
    h2 { font-weight: normal; }
    a { font-weight: bold; }
    a:hover { color: crimson; }
    code { font-size: 75%; }
    footer { text-align: center; margin: 2rem 0; font-size: 90%; }
    footer a { text-decoration: none; color: #777; }
</style>

</head>
<body>

<header class="container">
<h1>
The power of vanilla JS and CSS<br />
<small>- a reminder -</small>
</h1>

<p>
Developing for the web these days can seem overwhelming. There is an
almost infinitely rich choice of libraries and frameworks to pick from.
You'll probably also need to implement a build step, version control
and a deploy pipeline. All before you've written a single line of code.
</p>

<p>
How about a fun suggestion? Let's take a step back and remind ourselves
just how succinct and powerful modern JavaScript and CSS can be, without
the need for any shiny extras.
</p>

<p>
Interested? Come with me then, on a journey to make a browser based game
using only vanilla js and CSS.
</p>

</header>

<main class="container">
<section>
<h2>The Idea</h2>

<p>
We'll be building a flag guessing game. The player is presented with a
flag and a multiple choice style list of answers.
</p>
</section>

<section>
<h2>Step 1. Basic structure</h2>
<p>
First off, we're going to need a list of countries and their respective
flags. Thankfully, we can harness the power of emojis for displaying the
flags, meaning we don't have to source or, even worse, create them
ourselves. I've prepared this in <a href="./js/data.json">JSON</a> form.
</p>

<p>
At its simplest the interface is going to show a flag emoji and five buttons:
<img src="./i/screenshot1.png" width="400px" style="margin: 1rem auto; display: block; border: 1px solid rgba(0,0,0,0.2); border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.5) 10px 10px 10px -10px" />
</p>

<p>
A dash of CSS using grid to center everything and relative sizes so it
displays nicely from the smallest screen up to the biggest monitor.
</p>


<p>
Grab a copy of our starter shim (<a href="step1.html">step1.html</a>). We will be building on this through out
the tutorial.
</p>

<p>
The file structure for our project looks like this:
</p>
<pre><code class="language-javascript">
  step1.html
  step2.html // etc
  js/
    data.json
    // more js files
  helpers/
    // we'll get to this in step 3.
  css/
  i/
</code></pre>

<p>
At the end of each section there will be a link to the our
code in it's current state.
</p>

</section>

<section>
<h2>Step 2. A Simple Prototype</h2>
<p>Let's get cracking. First off, we need to grab our <a href="./js/data.json">data.json</a> file</p>

<pre><code class="language-javascript">
    async function loadCountries(file) {
      try {
        const response = await fetch(file);
        return await response.json();
      } catch (error) {
        throw new Error(error);
      }
    }

    // data.json contains an array of objects that looks like this:
    // { flag: <Flag emoji>, name: <Country name>}
    loadCountries('./js/data.json')
    .then((data) => {
        startGame(data.countries)
    });
</code></pre>

<p>
Now that we have the data, we can start the game. The following
code is generously commented. Take a couple of minutes to read
through and get a handle on what is happening.
</p>

<pre><code class="language-javascript">
    function startGame(countries) {
      // we want a randomized list of countries
      // first, get all the keys from our JSON object
      // now shuffle
      shuffle(countries);

      // pick answer
      let answer = countries.shift();

      // pick 4 more countries, merge our answer and shuffle
      let selected = shuffle([answer, ...countries.slice(0, 4)]);

      // update the DOM, starting with the flag
      document.querySelector('h2.flag').innerText = answer.flag;
      // update each button with a country name
      document.querySelectorAll('.suggestions button')
          .forEach((button, index) => {
        const countryName = selected[index].name;
        button.innerText = countryName;
        // this will allow us to check if the clicked button
        // corresponds to the answer
        button.dataset.correct = (countryName === answer.name);
        button.onclick = checkAnswer;
      })
    }
</code></pre>

<p>
And some logic to check the answer:
</p>

<pre><code class="language-javascript">
    function checkAnswer(e) {
      const button = e.target;
      if (button.dataset.correct === 'true') {
        button.classList.add('correct');
        alert('Correct! Well done!');
      } else {
        button.classList.add('wrong');
        alert('Wrong answer try again');
      }
    }
</code></pre>

<p>
You've probably noticed that our <code>startGame</code> function calls a shuffle function.
Here is a simple implementation of the Fisher-Yates algorithm:
</p>

<pre><code class="language-javascript">
    // Fisher-Yates shuffle
    // https://bost.ocks.org/mike/shuffle/
    function shuffle(array) {
      var m = array.length, t, i;

      // While there remain elements to shuffle…
      while (m) {

        // Pick a remaining element…
        i = Math.floor(Math.random() * m--);

        // And swap it with the current element.
        t = array[m];
        array[m] = array[i];
        array[i] = t;
      }

      return array;

    }
</code></pre>

</section>

<section>
<h2>Step 3. A bit of class</h2>
<p>
Time for a bit of housekeeping. Modern libraries and frameworks often force
certain conventions that help apply structure to apps. As things start to
grow this makes sense and having all code in one file soon gets messy. Let's
leverage the power of modules to keep our code, errm, modular. Update your
HTML file, replacing the inline script with this:
</p>

<script type="text/plain" class="language-markup">
  <script type="module" src="./js/step3.js"></script>
</script>

<p>
Now, in js/step3.js we can load our helpers:
</p>

<pre><code class="language-javascript">
  import loadCountries from "./helpers/loadCountries.js";
  import shuffle from "./helpers/shuffle.js";
</code></pre>

<p>
Be sure to move the shuffle and loadCountries functions to their respective files.
</p>

<p>
<b>Note:</b> Ideally we would also import our data.json as a module but,
unfortunately, Firefox does not support import assertions.
</p>

<p>
You'll also need to start each function with export default. For example:
</p>

<pre><code class="language-javascript">
  export default function shuffle(array) {
  ...
</code></pre>

<p>
We'll also encapsulate our game logic in a Game class. This helps maintain the integrity
of the data and makes the code more secure and maintainable. Take a minute to read
through the code comments
</p>

<pre><code class="language-javascript">
loadCountries('js/data.json')
  .then((data) => {
    const countries = data.countries;
    const game = new Game(countries);
    game.start();
  });

class Game {
  constructor(countries) {
    // because we shift & slice the array we'll need to keep
    // an intact copy
    this.masterCountries = countries;
    // easier access to elements
    this.DOM = {
      flag: document.querySelector('h2.flag'),
      answerButtons: document.querySelectorAll('.suggestions button')
    }

    // trigger the checkAnswer method when clicked
    this.DOM.answerButtons.forEach((button) => {
      button.onclick = (e) => {
        this.checkAnswer(e.target);
      }
    })

  }

  start() {

    // note: using the spread operator allows us to make
    // a copy of the array rather than a reference which
    // would mean changes to countries affects masterCountries
    // see 4.3 https://github.com/airbnb/javascript#arrays
    this.countries = shuffle([...this.masterCountries]);
    // get our answer & remove from the array so
    // it doesn't repeat.
    const answer = this.countries.shift();
    // pick 4 more countries, merge our answer and shuffle
    const selected = shuffle([answer, ...this.countries.slice(0, 4)]);


    // update the DOM, starting with the flag
    this.DOM.flag.innerText = answer.flag;
    // update each button with a country name
    selected.forEach((country, index) => {
      const button = this.DOM.answerButtons[index];
      // remove any classes from previous turn
      button.classList.remove('correct', 'wrong');
      button.innerText = country.name;
      button.dataset.correct = country.name === answer.name;
    });
  }

  checkAnswer(button) {
    const correct = button.dataset.correct === 'true';

    if (correct) {
      button.classList.add('correct');
      alert('Correct! Well done!');
      this.start();
    } else {
      button.classList.add('wrong');
      alert('Wrong answer try again');
    }
  }
}
</code></pre>

</section>

<section>
<h2>Step 4. Scoring And A Gameover Screen</h2>

<p>
Let's update the Game constructor to handle multiple rounds:
</p>
<pre><code class="language-css">
class Game {
  constructor(countries, numTurns = 3) {
    // number of turns in a game
    this.numTurns = numTurns;
    ...
</code></pre>

<p>
Our DOM will need to be updated so we can handle the game over
state, add a replay button and display the score.
</p>

<script type="text/plain" class="language-markup">
    <main>
      <div class="score">0</div>

      <section class="play">
      ...
      </section>

      <section class="gameover hide">
       <h2>Game Over</h2>
        <p>You scored:
          <span class="result">
          </span>
        </p>
        <button class="replay">Play again</button>
      </section>
    </main>
</script>

<p>We just hide the game over section until it is required.</p>

<p>Now, add references to these new DOM elements in our game
constructor:</p>

<pre><code class="language-javascript">
    this.DOM = {
      score: document.querySelector('.score'),
      play: document.querySelector('.play'),
      gameover: document.querySelector('.gameover'),
      result: document.querySelector('.result'),
      flag: document.querySelector('h2.flag'),
      answerButtons: document.querySelectorAll('.suggestions button'),
      replayButtons: document.querySelectorAll('button.replay'),
    }
</code></pre>

<p>We'll also tidy up our Game start method, moving the logic
for displaying the countries to a separate method. This
will help keep things clean and manageable</p>
<pre><code class="language-css">

  start() {
    this.countries = shuffle([...this.masterCountries]);
    this.score = 0;
    this.turn = 0;
    this.updateScore();
    this.showCountries();
  }

  showCountries() {
    // get our answer
    const answer = this.countries.shift();
    // pick 4 more countries, merge our answer and shuffle
    const selected = shuffle([answer, ...this.countries.slice(0, 4)]);

    // update the DOM, starting with the flag
    this.DOM.flag.innerText = answer.flag;
    // update each button with a country name
    selected.forEach((country, index) => {
      const button = this.DOM.answerButtons[index];
      // remove any classes from previous turn
      button.classList.remove('correct', 'wrong');
      button.innerText = country.name;
      button.dataset.correct = country.name === answer.name;
    });

  }

  nextTurn() {
    const wrongAnswers = document.querySelectorAll('button.wrong')
          .length;
    this.turn += 1;
    if (wrongAnswers === 0) {
      this.score += 1;
      this.updateScore();
    }

    if (this.turn === this.numTurns) {
      this.gameOver();
    } else {
      this.showCountries();
    }
  }

  updateScore() {
    this.DOM.score.innerText = this.score;
  }

  gameOver() {
    this.DOM.play.classList.add('hide');
    this.DOM.gameover.classList.remove('hide');
    this.DOM.result.innerText = `${this.score} out of ${this.numTurns}`;
  }
</code></pre>

<p>
At the bottom of the Game constructor method we will
listen for clicks to the replay button(s). In the
event of a click we restart by calling the start method.
</p>

<pre><code class="language-javascript">
    this.DOM.replayButtons.forEach((button) => {
      button.onclick = (e) => {
        this.start();
      }
    });
</code></pre>

<p>
Lastly, let's add a dash of style to the buttons, position the score and
add our .hide class to toggle game over as needed.
</p>
<pre><code class="language-css">
button.correct { background: darkgreen; color: #fff; }
button.wrong { background: darkred; color: #fff; }

.score { position: absolute; top: 1rem; left: 50%; font-size: 2rem; }
.hide { display: none; }
</code></pre>

<p>Progress! We now have a very simple game.
It is a little bland, though. Let's address that
in the next step.
</p>

<p><a href="step4.html">Code from this step</a></p>

</section>

<section>
<h2>Step 5. Bring The Bling!</h2>
<p>CSS animations are a very simple and succinct way to
bring static elements and interfaces to life.</p>

<p>
<a href="https://developer.mozilla.org/en-US/docs/Web/CSS/@keyframes">Keyframes</a>
allow us to define keyframes of an animation sequence with changing
CSS properties. Consider this for sliding our country list on and off screen:
</p>

<pre><code class="language-css">
.slide-off { animation: 0.75s slide-off ease-out forwards; animation-delay: 1s;}
.slide-on { animation: 0.75s slide-on ease-in; }

@keyframes slide-off {
  from { opacity: 1; transform: translateX(0); }
  to { opacity: 0; transform: translateX(50vw); }
}
@keyframes slide-on {
  from { opacity: 0; transform: translateX(-50vw); }
  to { opacity: 1; transform: translateX(0); }
}
</code></pre>

<p>We can apply the sliding effect when starting the game...</p>
<pre><code class="language-css">
  start() {
    // reset dom elements
    this.DOM.gameover.classList.add('hide');
    this.DOM.play.classList.remove('hide');
    this.DOM.play.classList.add('slide-on');
    ...
  }
</code></pre>

<p>...and in the nextTurn method</p>
<pre><code class="language-css">
  nextTurn() {
    ...
    if (this.turn === this.numTurns) {
      this.gameOver();
    } else {
      this.DOM.play.classList.remove('slide-on');
      this.DOM.play.classList.add('slide-off');
    }
  }
</code></pre>

<p>
We also need to call the nextTurn method once we've checked the
answer. Update the checkAnswer method to achieve this:
</p>
<pre><code class="language-css">
  checkAnswer(button) {
    const correct = button.dataset.correct === 'true';

    if (correct) {
      button.classList.add('correct');
      this.nextTurn();
    } else {
      button.classList.add('wrong');
    }
  }
</code></pre>

<p>
Once the slide-off animation has finished we need to
slide it back on and update the country list. We could
set a timeout, based on animation length, and the perform
this logic. Thankfully, there is an easier way using
the <a href="https://developer.mozilla.org/en-US/docs/Web/API/Element/animationend_event">animationend</a>
event:
</p>
<pre><code class="language-css">
    // listen to animation end events
    // in the case of .slide-on, we change the card,
    // then move it back on screen
    this.DOM.play.addEventListener('animationend', (e) => {
      const targetClass = e.target.classList;
      if (targetClass.contains('slide-off')) {
        this.showCountries();
        targetClass.remove('slide-off', 'no-delay');
        targetClass.add('slide-on');
      }
    });
</code></pre>

<p><a href="step5.html">Code from this step</a></p>


</section>

<section>
<h2>Step 6. Final Touches</h2>
<p>Wouldn't it be nice to add a title screen. This way the user
is given a bit of context and not thrown straight into the game</p>

<p>Our markup will look like this:</p>
<script type="text/plain" class="language-markup">
      <!-- hide score until game.start() is called -->
      <div class="score hide">0</div>

      <section class="intro fade-in">
       <h1>
          Guess the flag
      </h1>
       <p class="guess">🌍</p>
      <p>How many can you recognize?</p>
      <button class="replay">Start</button>
      </section>


      <!-- hide play until game.start() is called -->
      <section class="play hide">
      ...
</script>

<p>
Let's hook the intro screen into the game.<br />
We'll need to add a reference to it in the DOM elements:
</p>
<pre><code class="language-javascript">
    // in Game constructor
    this.DOM = {
      intro: document.querySelector('.intro'),
      ....
</code></pre>

<p>
Then simply hide it when starting the game:
</p>
<pre><code class="language-javascript">
  start() {
    // hide intro
    this.DOM.intro.classList.add('hide');
    // show score
    this.DOM.score.classList.remove('hide');
    ...
</code></pre>

<p>
Also, don't forget to add the new styling:
</p>
<pre><code class="language-css">
section.intro p { margin-bottom: 2rem; }
section.intro p.guess { font-size: 8rem; }
.fade-in { opacity: 0; animation: 1s fade-in ease-out forwards; }
@keyframes fade-in {
  from { opacity: 0; }
  to { opacity: 1; }
}
</code></pre>

<p>
Wouldn't it be nice to provide the player with a rating
based on their score? This is super easy to implement.
As can be seen, in the updated gameOver method:
</p>

<pre><code class="language-javascript">
    const ratings = ['💩','🤣','😴','🤪','👎','😓','😅','😃','🤓','🔥','⭐'];
    const percentage = (this.score / this.numTurns) * 100;
    // calculate rating based on score
    const rating = Math.ceil(percentage / ratings.length);

    this.DOM.play.classList.add('hide');
    this.DOM.gameover.classList.remove('hide');
    // reuse our fade-in class from the intro
    this.DOM.gameover.classList.add('fade-in');
    this.DOM.result.innerHTML = `
      ${this.score} out of ${this.numTurns}
      <br />
      Your rating: ${this.ratings[rating]}
      `;
  }
</code></pre>

<p>
One final finishing touch; a nice animation when the player guesses
correctly. We can turn once more to CSS animations to achieve this
effect.
</p>

<pre><code class="language-css">


button::before { content: ' '; background: url(../i/star.svg); height: 32px; width: 32px; position: absolute; bottom: -2rem; left: -1rem; opacity: 0; }
button::after {  content: ' '; background: url(../i/star.svg); height: 32px; width: 32px; position: absolute; bottom: -2rem; right: -2rem; opacity: 0; }
/* for the above to work the button must be positioned relatively */
button { position: relative; }

button.correct::before { animation: sparkle .5s ease-out forwards; }
button.correct::after { animation: sparkle2 .75s ease-out forwards; }

@keyframes sparkle {
  from { opacity: 0; bottom: -2rem; scale: 0.5 }
  to { opacity: 0.5; bottom: 1rem; scale: 0.8; left: -2rem; transform: rotate(90deg); }
}

@keyframes sparkle2 {
  from { opacity: 0; bottom: -2rem; scale: 0.2}
  to { opacity: 0.7; bottom: -1rem; scale: 1; right: -3rem; transform: rotate(-45deg); }
}
</code></pre>

<p>
We use the ::before and ::after <a href="https://developer.mozilla.org/en-US/docs/Web/CSS/::before">pseudo elements</a>
to attach background image (<a href="./i/star.svg">star.svg</a>) but keep it hidden via
setting opacity to 0. <br />
It is then activated by invoking the sparkle animation
when the button has the class name correct. <br />
Remember, we already apply this class to the button
when the correct answer is selected.
</p>

<p><a href="step6.html">Code from this step</a></p>


</section>


<section>
<h2>Wrap Up And Some Extra Ideas</h2>
<p>
In less than 200 lines of (liberally commented) javascript we have a fully
working, mobile friendly game. And not a single dependency or library in sight!
</p>

<p>
Of course, there are endless features and improvements we could add to our game.
If you fancy a challenge here are a few ideas:
<ul>
  <li>Add basic sound effects for correct and incorrect answers.</li>
  <li>Make the game available offline using webworkers</li>
  <li>Store stats such as number of plays, overall ratings in localstorage and display</li>
  <li>Add a way to share your score and challenge friends on social media. </li>
</ul>
</p>
</section>

</main>

<footer>
      <p><a href="https://eoinmcgrath.com">by Eoin McGrath</a></p>
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