JavaScript JavaScript and the DOM Responding to User Interaction Listening for Events with addEventListener()

Posted by Lawrence Babay
Lawrence Babay
6,941 Points

"Add item and Remove last item" buttons not working

Hi all,

I'm not sure what happened but after adding the 'listItems.addEventListner' the "Add item and Remove last item" buttons are not working anymore.

Thanks, Lawrence

Steven Parker
Steven Parker
172,047 Points
Steven Parker
Steven Parker
172,047 Points

To facilitate analysis and an answer, you'll need to show your code. Or even better, make a snapshot of your workspace and post the link to it here.

3 Answers

Steven Parker
Steven Parker
172,047 Points
Steven Parker
Steven Parker
172,047 Points

Despite the chaotic code display, I managed to spot this:

for (let i = 0; i <= listItems.length; i++)

The length is always greater than the highest possible index value, so the loop condition should be less than ("<") the length (instead of "<=").

Lawrence Babay
Lawrence Babay
6,941 Points
Lawrence Babay
Lawrence Babay
6,941 Points

Hi Steven,

here's my code. Sorry about that.

<!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> <button class="removeItemButton">Remove last 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'); const removeItemButton = document.querySelector('button.removeItemButton'); const listItems = document.getElementsByTagName('li');

for (let i = 0; i <= listItems.length; i++) { listItems[i].addEventListener('mouseover', () => { listItems[i].textContent = listItems[i].textContent.toUpperCase();
}); listItems[i].addEventListener('mouseout', () => { listItems[i].textContent = listItems[i].textContent.toLowerCase();
}); }

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 + ':'
descriptionInput.value = ''; });

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

removeItemButton.addEventListener('click', () => { let ul = document.getElementsByTagName('ul')[0]; let li = document.querySelector('li:last-child'); ul.removeChild(li);

});

Thanks, Lawrence

Steven Parker
Steven Parker
172,047 Points
Steven Parker
Steven Parker
172,047 Points

When posting code directly in the forum, use the instructions for code formatting in the Markdown Cheatsheet pop-up below the "Add an Answer" area. :arrow_heading_down:   Or watch this video on code formatting

Lawrence Babay
Lawrence Babay
6,941 Points
Lawrence Babay
Lawrence Babay
6,941 Points

Hi Steven,

Sorry about that. I'm pretty new with this workspaces. Thanks for the link and for finding the issue.

Lawrence