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JavaScript JavaScript and the DOM (Retiring) Making Changes to the DOM Creating New DOM Elements

Posted by tarascript
.a{fill-rule:evenodd;}techdegree
tarascript
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
6,650 Points
Stephan Olsen
Stephan Olsen
6,650 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.

tarascript
seal-mask
.a{fill-rule:evenodd;}techdegree
tarascript
Full Stack JavaScript Techdegree Student 10,613 Points
tarascript
.a{fill-rule:evenodd;}techdegree
tarascript
Full Stack JavaScript Techdegree Student 10,613 Points

Great, thank you! Got it working now.