Advent of JavaScript, Day 3

Challenge #3 is creating a keyboard game:

With the project files downloaded and codesandbox‘d into a live CodeSandbox, I’m ready to get going!

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Again, let’s start with the User Requirements and speculate how I can solve these:

Users should be able to:

• See the keyboard centered on the page

Done!

• Whenever a user hovers over a specific key it will change colors
  • White keys will change to yellow #ffd200

Done!

• Black keys will change to pink #f40082

Done!

• When a user clicks on a specific key, it will play an audio clip.

This seems straightforward – new Audio(url).

• The audio clips are numbered, but I did not specifically number the keys. You can pick which key should be associated with each audio file.

The files are named audio/key-{1-23}.mp3, so the initial implementation can just increment by key position.

• If a user clicks on one key, then immediately clicks on a second key. The 2 files should both play. Meaning, clicking on one key will not stop an existing audio file from playing.

What this tells me is that there won’t be a re-use of variable references.

Initial Approach

• Vanilla JS (no libraries), since there doesn’t seem to be much complexity here

• document.querySelectorAll('.piano a') to find all keys

• .addEventListener('click', ...) to listen for clicks

• new Audio(url) to create & .play the audio

  The URLs load asynchronously, so it may be best to initialize these immediately and .play once clicked.

Making it Work

This wasn’t much of a challenge. I was able to get this completed while an episode of Spongebob was playing…

Anyway, the only surprise was with the SVG keys being out of order: the <a> elements aren’t in left-to-write order, but seemingly random in the SVG.

To solve this, I used .sort to find the mid-point of each key and order those left-to-right:

const keyElements = Array.from(document.querySelectorAll('.piano a'))

keyElements.sort((a, b) => {
  const aRect = a.getBoundingClientRect()
  const aMiddle = aRect.left + aRect.width / 2

  const bRect = b.getBoundingClientRect()
  const bMiddle = bRect.left + bRect.width / 2

  return aMiddle - bMiddle
})

Then, I mapped those keys to the sound they would play:

const keyAudios = keyElements.map((keyElement, i) => {
  return new Audio(`audio/key-${i + 1}.mp3`)
})

(The browser automatically marks these as preload, so they should be ready to go once you click a key.)

One way to associate clicks-to-keys is to keyElements.forEach(keyElement, ...) and keyElement.addEventListener('click', ...).

An alternative is to use window.addEventListener('click', ...) so there’s one event listener rather than N (23).

This optimization isn’t necessary here, but can be a good idea when indescriminately adding events to an unknown number of elements:

• Points on a graph
• Rows in a table
• Links on a page
• etc.

window.addEventListener('click', (event) => {
  // click is on the `<path>`, so traverse up to the <a>
  const a = event.target.parentNode

  if (!keyElements.includes(a)) {
    return
  }

  event.preventDefault()

  const i = keyElements.indexOf(a)
  const audio = keyAudios[i]

  audio.currentTime = 0
  audio.play()
})

Since each keyAudios is separate, the sounds automatically overlap.

But, I wanted to make sure repeatedly clicking a key would repeat the sound from the beginning. The Audio API does not have a .stop or .restart method, so setting audio.currentTime = 0 effectively accomplishes the same thing.