JavaScript JavaScript and the DOM Making Changes to the DOM Creating New DOM Elements

Nicolas Bastos
Nicolas Bastos
4,209 Points

Error: Uncaught TypeError: Cannot read property 'addEventListener' of null

I dont know why I get that error, everything seems correct. JS:

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 addItemButton = document.querySelector("input.addItemButton");
const addItemInput = document.querySelector("input.addItemInput");


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.getElementsByTagName("ul")[0];
  let li = document.createElement("li");
  li.textContent = addItemInput.value;
  ul.appendChild(li);

});
Timothy Schmidt
Timothy Schmidt
4,806 Points

There's no way to test it without the html to go along with it. Most likely, one of your document.querySelector or document.getElementById calls are failing. Make sure all of your variables have the values you're expecting.

Nicolas Bastos
Nicolas Bastos
4,209 Points

@TimothySchmidt here is the HTML:

<!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 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>

1 Answer

Timothy Schmidt
Timothy Schmidt
4,806 Points

The error is on this line:

const addItemButton = document.querySelector("input.addItemButton");

The element type isn't an input, it's a button. The following code works.

const addItemButton = document.querySelector("button.addItemButton");