How do I compare two cards' classnames

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Javascript

I'm a JS beginner self-learner.

I want to make a simple app for matching words. There are four words and they form 2 pairs. I get the error message that activeCards are undefined , although they are defined as const activeCards.

<pre><div class="wrapper">
      <div class="main-message">
        <h1>Match the words to make correct greetings in Portuguese</h1>
      </div>

      <!-- ### main cards ### -->
      <div class="left-bottom">
        <div class="card set2 set2a">Boa</div>
        <div class="card set1 set1a">Bom</div>
      </div>
      <div class="right-bottom">
        <div class="card set1 set1b">dia</div>
        <div class="card set2 set2b">tarde</div>
      </div>
    </div>

*,
*::before,
*::after {
  padding: 0;
  margin: 0;
  box-sizing: border-box;
}

/* ### layout ### */

.wrapper {
  position: relative;
  width: 100%;
  height: 100vh;
}

.main-message {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 30vh;
  background-color: #999;
  display: flex;
  align-items: center;
  justify-content: center;
  font-family:'Franklin Gothic Medium', 'Arial Narrow', Arial, sans-serif;
}

h1 {
  display: block;
  border: 1px solid black;
  padding: 0.2rem 0.4rem;
  border-radius: 10px;
}

.left-bottom {
  position: absolute;
  top: 30vh;
  left: 0;
  width: 50%;
  height: 70vh;
  background-color: yellow;
}

.right-bottom {
  position: absolute;
  top: 30vh;
  right: 0;
  width: 50%;
  height: 70vh;
  background-color: yellowgreen;
}

.left-bottom, .right-bottom {
  display: flex;
  align-items: center;
  justify-content: center;
  flex-direction: column;
}

.card {
  width: 100px;
  height: 100px;
  border: 1px solid black;
  background-color: transparent;
  font-size: 2rem;
  display: flex;
  align-items: center;
  justify-content: center;
  margin-top: 1rem;
  border-radius: 20px;
  -webkit-box-shadow: 3px 4px 24px 0px rgba(66, 68, 90, 0.54);
  -moz-box-shadow: 3px 4px 24px 0px rgba(66, 68, 90, 0.54);
  box-shadow: 3px 4px 24px 0px rgba(66, 68, 90, 0.54);
  transition: all 0.3s;
  cursor: pointer;
}

.selected {
  background-color: green;
}

  <pre>
const card1a = document.querySelector(".set1a");
const card1b = document.querySelector(".set1b");
const card2a = document.querySelector(".set2a");
const card2b = document.querySelector(".set2b");



let cards = document.querySelectorAll(".card");
cards = [...cards];
let activeCard = '';
const activeCards = [];

const clickCard = function() {
    activeCard = this;

    cards.forEach( card => card.addEventListener("click", function(){
        console.log("click");
        card.classList.add("selected");

        if( activeCards.length === 0) {
            activeCards[0] = activeCard;
            console.log("first card");
            return;
        } else {
            console.log("second card");
            cards.forEach(card => card.removeEventListener("click", clickCard));
            activeCards[1] = activeCard;
            if (activeCards[0].classList.contains("set1") && activeCards[1].classList.contains("set1") || activeCards[0].classList.contains("set2") && activeCards[1].classList.contains("set2")){
                console.log("You found a match.");
            }
        
        }
    }))
}

clickCard();

What I have tried:

I tried to google a memory game and followed the guide there but doesn't work here.