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

lionelsurmont
lionelsurmont
7,092 Points

Error in Visual Studio but no apparent error in the code

Hi!

I've got an error in Visual Studio 2017. The variable listItems, whatever it is refering to is not recognized (Uncaught ReferenceError: listItems is not defined).

I copied the code in the Workspace and it had absolutely no problem.

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');
const firstItem = listItems[0];


firstItem.addEventListener('mouseover', () => {
    firstItem.textContent = firstItem.textContent.toUpperCase();
    console.log('Mouse over');
});

firstItem.addEventListener('mouseout', () => {
    firstItem.textContent = firstItem.textContent.toLowerCase();
    console.log('Mouse out');
});

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);
});

1 Answer

Steven Parker
Steven Parker
185,909 Points

It's defined on line 9:

const listItems = document.getElementsByTagName('li');

I'd guess something happened while moving it, perhaps that line got lost or a typo changed the name.