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Aakash Srivastav
Full Stack JavaScript Techdegree Student 11,625 PointsListening for Events with addEventListener()
I tried this , but it didn't work . Why? -
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.querySelectorAll();
const toUpperCase = event => {
event.target.textContent.toUpperCase();
}
const toLowerCase = event => {
event.target.textContent.toLowerCase();
}
listItems.addEventListener( 'mouseOver' , toUpperCase);
listItems.addEventListener( 'mouseOut' , toLowerCase);
//here
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);
});
2 Answers

Adam Beer
11,313 PointsPlease change your last "querySelectorAll()" to "getElementByTagName()". And correct your code. Please check again the video.

Steven Parker
216,175 PointsThe call to "querySelectorAll" requires a selector string argument to operate correctly.
Also, the "toUpperCase" and "toLowerCase" methods don't alter the strings they are applied to, they just return a new string with the changes. For this to be useful in a program, the returned value would need to be assigned to a variable or passed as an argument to a function.
For future questions, to facilitate a complete analysis of complex project issues, make a snapshot of your workspace and post the link to it here.
Steven Parker
216,175 PointsSteven Parker
216,175 PointsYou probably meant "getElementsByTagName" (with an "s"), and neither one will work correctly without an argument.
Adam Beer
11,313 PointsAdam Beer
11,313 PointsI did not write down the complete solution. After that I saw that the code was bad several places at the beginning