Piano Keys Project HELP!

Hi, I’m starting the Piano Keys project which is focused on DOM events, and I’m already confused at steps 4-6. I don’t understand why we do this:

// Write a named function with event handler properties
const eventAssignment = (note) => { 
  note.onmousedown = function() {
    keyPlay(event);
  };
  note.onmouseup = function() {
    keyReturn(event);
  };
}

// Write a loop that runs the array elements through the function
notes.forEach(eventAssignment);

My original idea was to do this:

const eventAssignment = (note) => {
  note.onmousedown = keyPlay;
  note.onmouseup = keyReturn;
}

notes.forEach(function(key) {
  eventAssignment(key);
});

Need help!!!

Here’s the full HTML and Javascript files:
Javascript:

// The keys and notes variables store the piano keys
const keys = ['c-key', 'd-key', 'e-key', 'f-key', 'g-key', 'a-key', 'b-key', 'high-c-key', 'c-sharp-key', 'd-sharp-key', 'f-sharp-key', 'g-sharp-key', 'a-sharp-key'];
const notes = [];
keys.forEach(function(key){
  notes.push(document.getElementById(key));
})

// Write named functions that change the color of the keys below
const keyPlay = (event) => {
  event.target.style.backgroundColor = 'pink';
}

const keyReturn = (event) => {
  event.target.style.backgroundColor = '';
} 

// Write a named function with event handler properties
const eventAssignment = (note) => { 
  note.onmousedown = function() {
    keyPlay(event);
  };
  note.onmouseup = function() {
    keyReturn(event);
  };
}

// Write a loop that runs the array elements through the function
notes.forEach(eventAssignment);

// These variables store the buttons that progress the user through the lyrics
let nextOne = document.getElementById('first-next-line');
let nextTwo = document.getElementById('second-next-line');
let nextThree = document.getElementById('third-next-line');
let startOver = document.getElementById('fourth-next-line');

// This variable stores the '-END' lyric element
let lastLyric = document.getElementById('column-optional');

// These statements are "hiding" all the progress buttons, but the first one
nextTwo.hidden = true;
nextThree.hidden = true;
startOver.hidden= true;

// Write anonymous event handler property and function for the first progress button


// Write anonymous event handler property and function for the second progress button


// Write anonymous event handler property and function for the third progress button


// This is the event handler property and function for the startOver button
startOver.onclick = function() {
  nextOne.hidden = false;
  startOver.hidden = true;
   document.getElementById('word-one').innerHTML = 'HAP-';
  document.getElementById('letter-note-one').innerHTML = 'G';
  document.getElementById('word-two').innerHTML = 'PY';
  document.getElementById('letter-note-two').innerHTML = 'G';
  document.getElementById('word-three').innerHTML = 'BIRTH-';
  document.getElementById('letter-note-three').innerHTML = 'A';
  document.getElementById('word-four').innerHTML = 'DAY';
  document.getElementById('letter-note-four').innerHTML = 'G';
  document.getElementById('word-five').innerHTML = 'TO';
  document.getElementById('letter-note-five').innerHTML = 'C';
  document.getElementById('word-six').innerHTML = 'YOU!';
  document.getElementById('letter-note-six').innerHTML = 'B';
}

HTML:

<!DOCTYPE html>
<html lang="en" >

<head>
  <meta charset="UTF-8">
  <link rel="stylesheet" href="style.css">
</head>

<body>
  <p class='title'>Piano Player</p>
  <p id='demo'>Follow the song below to play  the piano.</p>
  <section class="piano">
    <section id='c-key' class="key">
      <section class='keynote'>C</section>
    </section>
    <section id='c-sharp-key' class="black-key">
      <section class='black-keynote'>C#</section>
    </section>
    <section id='d-key' class="key">
      <section class='keynote'>D</section>
    </section>
    <section id='d-sharp-key' class="black-key">
      <section class='black-keynote'>D#</section>
    </section>
    <section id='e-key' class="key">
      <section class='keynote'>E</section>
    </section>
    <section id='f-key' class="key">
      <section class='keynote'>F</section>
    </section>
    <section id='f-sharp-key' class="black-key">
      <section class='black-keynote'>F#</section>
    </section>
    <section id='g-key' class="key">
      <section class='keynote'>G</section>
    </section>
    <section id='g-sharp-key' class="black-key">
      <section class='black-keynote'>G#</section>
    </section>
    <section id='a-key' class="key">
      <section class='keynote'>A</section>
    </section>
    <section id='a-sharp-key' class="black-key">
      <section class='black-keynote'>A#</section>
    </section>
    <section id='b-key' class="key">
      <section class='keynote'>B</section>
    </section>
    <section id='high-c-key' class="key">
      <div class='keynote'>C</div>
    </section>
  </section>

  <section id='lyrics'>
    <section id='column-one'>
      <section id="word-one">HAP-</section>
      <section id="letter-note-one">G</section>
    </section>
    <section id='column-two'>
      <section id="word-two">PY</section>
      <section id="letter-note-two">G</section>
    </section>
    <section id='column-three'>
      <section id="word-three">BIRTH-</section>
      <section id="letter-note-three">A</section>
    </section>
    <section id='column-four'>
      <section id="word-four">DAY</section>
      <section id="letter-note-four">G</section>
    </section>
    <section id='column-five'>
      <section id="word-five">TO</section>
      <section id="letter-note-five">C</section>
    </section>
    <section id='column-six'>
      <section id="word-six">YOU</section>
      <section id="letter-note-six">B</section>
    </section>
    <section id='column-optional' class='column-optional'>
      <section id="word-optional">END</section>
      <section id="letter-note-optional">A</section>
    </section>

    <button id="first-next-line">Line 2</button>
    <button id="second-next-line">Line 3</button>
    <button id="third-next-line">Line 4</button>
    <button id="fourth-next-line">Reset</button>
  </section>

  <script  src="main.js"></script>

</body>
</html>