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

Tara Hackley
Tara Hackley
Full Stack JavaScript Techdegree Student 10,613 Points

Unable to find what's causing this: Uncaught TypeError: Cannot read property 'addEventListener' of null at app.js:24

Here is the JS file:

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 li = document.createElement("li");
 li.textContent = addItemInput.value;
});

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 id="addItemButton">Add Item</button>
    </div>
    <script src="app.js"></script>
  </body>
</html>

2 Answers

Stephan Olsen
Stephan Olsen
6,647 Points

In your html you're giving your button an ID, but in your selector you're referencing it by a class.

// Assigning an ID to the button
<button id="addItemButton">Add Item</button> 
// Referencing the button by a class
const addItemButton = document.querySelector("button.addItemButton");

So basically you just need to select the button by its ID.