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JavaScript

Posted by Darrin Fagley
Darrin Fagley
12,432 Points

Getting strange error when trying to use appendChild()

When try to add an item as in the video I receiving the following error: app.js:27 Uncaught TypeError: Cannot read property 'appendChild' of undefined at HTMLButtonElement.<anonymous> (app.js:27)

Not sure where my mistake is, I have checked and double checked and do not see a syntax error, any help would be appreciated.

<!DOCTYPE html>
<html>
  <head>
    <title>JavaScript and the DOM</title>
    <link rel="stylesheet" href="css/style.css" />
  </head>
  <body>
    <h1 id="myHeading">JavaScript and the DOM</h1>
    <p>Making a web page interactive</p>
    <button id="toggleList">Hide list</button>
    <div class="list">
      <p title="label" class="description">Things that are purple:</p>
      <input type="text" class="description" />
      <button class="description">Change list description</button>
      <ul>
        <li>grapes</li>
        <li>amethyst</li>
        <li>lavender</li>
        <li>plums</li>
      </ul>
      <input type="text" class="addItemInput" />
      <button class="addItemButton">Add item</button>
    </div>
    <script src="app.js"></script>
  </body>
</html>

const toggleList = document.getElementById('toggleList');
const listDiv = document.querySelector('.list');
const descriptionInput = document.querySelector('input.description');
const descriptionP = document.querySelector('p.description');
const descriptionButton = document.querySelector('button.description');
const addItemInput = document.querySelector('input.addItemInput');
const addItemButton = document.querySelector('button.addItemButton');

toggleList.addEventListener('click', () => {
  if (listDiv.style.display === 'none') {
    toggleList.textContent = 'Hide list';
    listDiv.style.display = 'block';
  } else {
    toggleList.textContent = 'Show list';
    listDiv.style.display = 'none';
  }
});

descriptionButton.addEventListener('click', () => {
  descriptionP.innerHTML = descriptionInput.value + ':';
});

addItemButton.addEventListener('click', () => {
  let ul = document.getElementsByClassName('ul')[0];
  let li = document.createElement('li');
  li.textContent = addItemInput.value;
  ul.appendChild(li);
});

1 Answer

Jonathan Grieve
MOD
Jonathan Grieve
Treehouse Moderator 91,253 Points
Jonathan Grieve
Jonathan Grieve
Treehouse Moderator 91,253 Points

Try getElementsByTagName rather than className for your ul variable. It's looking for a collection of elements that have the class of ul, at the moment. :)

Darrin Fagley
Darrin Fagley
12,432 Points

Ah!!! I totally didn't see that thank you!