Event handlers usage optimization in JavaScript

Too many handlers hung on elements eat up a lot of RAM and lead to page freezes.

Let's look at an example. Let's have some list:

html<ul></ul>

We get a reference to this list into a variable:

javascriptlet ul = document.querySelector('ul');

Now let's fill our list with li tags, attaching a click handler to them:

javascriptfor (let i = 1; i <= 1000; i++) {
  let li = document.createElement('li');
  li.textContent = i;
  ul.append(li);
  
  li.addEventListener('click', function() {
    console.log(this.textContent);
  });
}

As a result, it turns out that we have 1000 handlers. This is a lot. For optimization, we can attach only one handler to the ul tag using a delegation.

Let's do that. First, let's just create the list items:

javascriptfor (let i = 1; i <= 1000; i++) {
  let li = document.createElement('li');
  li.textContent = i;
  ul.append(li);
}

Now let's use delegation of the event handler:

javascriptul.addEventListener('click', function(event) {
  let li = event.target.closest('li');
  
  if (li) {
    console.log(li.textContent);
  }
});