What's Event Bubbling?

When an event occurs on a DOM element, that event does not entirely occur on that just one element. In the Bubbling Phase, the event bubbles up or it goes to its parent, to its grandparents, to its grandparent's parent until it reaches all the way to the window.

If we have an example markup like this.

<div class="grandparent">
  <div class="parent">
    <div class="child">1</div>
  </div>
</div>

And our js code.

function addEvent(el, event, callback, isCapture = false) {
  if (!el || !event || !callback || typeof callback !== 'function') return;
  if (typeof el === 'string') {
    el = document.querySelector(el);
  }
  el.addEventListener(event, callback, isCapture);
}

addEvent(document, 'DOMContentLoaded', () => {
  const child = document.querySelector('.child');
  const parent = document.querySelector('.parent');
  const grandparent = document.querySelector('.grandparent');

  addEvent(child, 'click', function (e) {
    console.log('child');
  });

  addEvent(parent, 'click', function (e) {
    console.log('parent');
  });

  addEvent(grandparent, 'click', function (e) {
    console.log('grandparent');
  });

  addEvent(document, 'click', function (e) {
    console.log('document');
  });

  addEvent('html', 'click', function (e) {
    console.log('html');
  });

  addEvent(window, 'click', function (e) {
    console.log('window');
  });
});

The addEventListener method has a third optional parameter useCapture with a default value of false the event will occur in the Bubbling phase if true the event will occur in the Capturing Phase. If we click on the child element it logs child,parent,grandparent, html, document and window respectively on the console. This is Event Bubbling.

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