How can I avoid to add same data as an existing in the certain container

Question

I want to add particular course only once in the following container and I tried to use this condition course.value !== added.textContent to avoid duplicates but it does nothing as I still see the duplicated courses.

For example, if you add html and add it again the condition acts like it is not available and I want to solve this.
the following are my code:

course.focus();
add.onclick = () => {
  let added = document.createElement('div');
  added.className = 'added';
  if ((course.value).trim()) {
    /*statement to avoid duplicate*/
    if (course.value !== added.textContent) {
      added.textContent = (course.value).replace(' ', '-');
      added.title = course.value + ' course';
      paste.appendChild(added);
      course.value = '';
    }
  }
}

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

body {
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
  background: #ff5;
}

.container {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  width: 50%;
  height: 50%;
}

#paste {
  width: 100%;
  height: 100%;
  border: 1px solid darkred;
  display: flex;
  flex-flow: row wrap;
  flex-basis: 1;
}

#copy {
  text-align: center;
}

input {
  width: 95%;
  font-weight: 900;
  height: 30px;
  outline: none;
  border: none;
  background: none;
  border-bottom: 2px solid green;
  border-radius: 5px;
  font-size: 18px;
  text-align: center;
}

button {
  width: 140px;
  height: 25px;
  border-radius: 10px;
  outline: none;
  border: none;
  font-size: 16px;
  margin-top: 15px;
  background: green;
  color: #fff;
  font-weight: 900;
}

.added {
  position: relative;
  margin: 3px;
  width: auto;
  padding: 5px;
  background: grey;
  border-radius: 5px;
  text-align: center;
  align-self: baseline;
}

<div class="container">
  <div id="copy">
    <input type="text" name="course" id="course" placeholder="Enter course">
    <button id="add">add</button>
  </div>
  <div id="paste"></div>
</div>

css html javascript

Unmitigated · Answer

Store all the added courses in a Set and check if the entered course already exists before appending it to the container. course.focus(); const courses = new Set; add.onclick = () => { let added = document.createElement('div'); added.className = 'added'; const val = course.value.trim(); if (val && !courses.has(val)){ courses.add(val); added.textContent = (course.value).replace(' ', '-'); added.title = course.value + ' course'; paste.appendChild(added); course.value = ''; } } * { box-sizing: border-box; padding: 0; margin: 0; } body { display: flex; justify-content: center; align-items: center; height: 100vh; background: #ff5; } .container { display: grid; grid-template-columns: repeat(2, 1fr); width: 50%; height: 50%; } #paste { width: 100%; height: 100%; border: 1px solid darkred; display: flex; flex-flow: row wrap; flex-basis: 1; } #copy { text-align: center; } input { width: 95%; font-weight: 900; height: 30px; outline: none; border: none; background: none; border-bottom: 2px solid green; border-radius: 5px; font-size: 18px; text-align: center; } button { width: 140px; height: 25px; border-radius: 10px; outline: none; border: none; font-size: 16px; margin-top: 15px; background: green; color: #fff; font-weight: 900; } .added { position: relative; margin: 3px; width: auto; padding: 5px; background: grey; border-radius: 5px; text-align: center; align-self: baseline; }

How can I avoid to add same data as an existing in the certain container

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