JavaScript - addEventListener on all created li elements

Question

So I have a simple script that adds "li" elements to the "ul" and assigns them a class. Now I want to change the class of "li" item on click event.

Here is the HTML:

<form class="form">
<input id="newInput" type="text" placeholder="Dodaj pozycję">
<button id="createNew" type="button">Dodaj</button>
</form>
<h2>Moja lista:</h2>
<div class="listBg">
<ul id="list">
</ul>
</div>
<button id="deleteAll" type="button">Wyczyść</button>

And JS:

function addItem() {
    var myList = document.getElementById("list"); // get the main list ("ul")
    var newListItem = document.createElement("li"); //create a new "li" element
    var itemText = document.getElementById("newInput").value; //read the input value from #newInput
    var listText = document.createTextNode(itemText); //create text node with calue from input
    newListItem.appendChild(listText); //add text node to new "li" element
    if (itemText === "") { // if input calue is empty
        alert("Pole nie może być puste"); // show this alert
    } else { // if it's not empty
        var x = document.createElement("span"); // create a new "span" element
        x.innerText = "X"; // add inner text to "span" element
        x.className = "closer"; // add class to "span" element
        myList.appendChild(newListItem); // add created "li" element to "ul"
        newListItem.className = "item"; // add class to new "li" element
        newListItem.appendChild(x); // add a "span" to new "li" element
        var itemText = document.getElementById("newInput"); // read current input value
        itemText.value = ""; // set current input calue to null
    }
};

I was thinking something like this should do the trick, but it's not working:

function itemDone() {
    var listItems = document.querySelectorAll("li");
    var i;
    for (i = 0; i < listItems.length; i++) {
    listItem[i].className = "itemDone";
};
};

var item = document.getElementsByClassName("item");
item.addEventListener("click", itemDone);

I'm fairly new to javascript so I would appreciate some explanation with the answer.

Answer 1

Use event delegation for the dynamically created elements. With this, you only need one event listener on the ul#list and it will work for all elements you dynamically attach to it:

document.getElementById("list").addEventListener("click",function(e) {
  if (e.target && e.target.matches("li.item")) {
    e.target.className = "foo"; // new class name here
    }
});

Here's a simplified example so you can see what happens with the code:

function addItem(i) {
  var li = document.createElement('li');
  li.appendChild(document.createTextNode(i));
  li.className = 'item';
  document.getElementById('list').appendChild(li);
}

var counter = 2;
document.getElementById('btn').addEventListener('click', function() {
  addItem(counter++);
});

document.getElementById("list").addEventListener("click", function(e) {
  if (e.target && e.target.matches("li.item")) {
    e.target.className = "foo"; // new class name here
    alert("clicked " + e.target.innerText);
  }
});

<ul id="list">
  <li class="item">1</li>
</ul>

<button id="btn">
  add item
</button>

Answer 2

You'll have to set the eventListener on each single item, as document.getElementsByClassName() returns a collection of items and you can't simply add an event listener to all of them with one call of addEventListener().

So, just like the loop you used in itemDone(), you'll have to iterate over all items and add the listener to them:

var items = document.getElementsByClassName("item");
for (var i = 0; i < items.length; i++) {
  items[i].addEventListener("click", itemDone);
}

As pointed out in the comments, you can also do so directly when creating the elements, so in your addItem() function, add:

newListItem.addEventListener("click", itemDone);

Answer 3

try this :

var item = document.getElementsByClassName("item");
for (var i = 0; i < item.length; i++) {
  item[i].addEventListener("click", itemDone);
}

Answer 4

function addItem(i) {
  var li = document.createElement('li');
  li.appendChild(document.createTextNode(i));
  li.className = 'item';
  document.getElementById('list').appendChild(li);
}

var counter = 2;
document.getElementById('btn').addEventListener('click', function() {
  addItem(counter++);
});

document.getElementById("list").addEventListener("click", function(e) {
  if (e.target && e.target.matches("li.item")) {
    e.target.className = "foo"; // new class name here
    alert("clicked " + e.target.innerText);
  }
});

<ul id="list">
  <li class="item">1</li>
  <li class="item">1</li>
  <li class="item">1</li>
  <li class="item">1</li>
  <li class="item">1</li>
</ul>

<button id="btn">
  add item
</button>