What is Event Bubbling? code example

Example 1: bubbling in javascript

<script>
	form.onclick = function(event) {
  event.target.style.backgroundColor = 'yellow';

  // chrome needs some time to paint yellow
  setTimeout(() => {
    alert("target = " + event.target.tagName + ", this=" + this.tagName);
    event.target.style.backgroundColor = ''
  }, 0);
};
</script>
<html>
<head>
  <meta charset="utf-8">
  <link rel="stylesheet" href="example.css">
</head>

<body>
  A click shows both <code>event.target</code> and <code>this</code> to compare:

  <form id="form">FORM
    <div>DIV
      <p>P</p>
    </div>
  </form>
</body>
</html>

<!-- A handler on a parent element can always get the details about where it actually happened.

The most deeply nested element that caused the event is called a target element, accessible as event.target.

Note the differences from this (=event.currentTarget):

event.target – is the “target” element that initiated the event, it doesn’t change through the bubbling process.
this – is the “current” element, the one that has a currently running handler on it.
For instance, if we have a single handler form.onclick, then it can “catch” all clicks inside the form. No matter where the click happened, it bubbles up to <form> and runs the handler.

In form.onclick handler:

this (=event.currentTarget) is the <form> element, because the handler runs on it.
event.target is the actual element inside the form that was clicked. -->

Example 2: what is event bubbling in javascript with example

<div>1
    <div>2
        <div>3
            <div>4
                <div>5</div>
            </div>
        </div>
    </div>
</div>
<button id="clear">clear output</button>
<section id="log"></section>

Example 3: what is event bubbling in javascript with example

p {
    line-height: 0;
}

div {
    display:inline-block;
    padding: 5px;

    background: #fff;
    border: 1px solid #aaa;
    cursor: pointer;
}

div:hover {
    border: 1px solid #faa;
    background: #fdd;
}

Example 4: what is event bubbling in javascript with example

var logElement = document.getElementById('log');

function log(msg) {
    logElement.innerHTML += ('<p>' + msg + '</p>');
}

function capture() {
    log('capture: ' + this.firstChild.nodeValue.trim());
}

function bubble() {
    log('bubble: ' + this.firstChild.nodeValue.trim());
}

function clearOutput() {
    logElement.innerHTML = "";
}

var divs = document.getElementsByTagName('div');
for (var i = 0; i < divs.length; i++) {
    divs[i].addEventListener('click', capture, true);
    divs[i].addEventListener('click', bubble, false);
}
var clearButton = document.getElementById('clear');
clearButton.addEventListener('click', clearOutput);

Example 5: event bubbling in javascript

“Inverse of event delegation. Also known as propagation, 
events on an element will “bubble up” and also fire on all parents.

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