event bubbling vs capturing

To demonstrate the difference between event bubbling and capturing modes, let's take an example where we have two HTML elements, one is inside another.
Both elements handle the click event. To make it simple, we use an inline onclick attribute to handle the event:
<div id="parent" onclick="console.log('parent clicked')">   <!-- Parent node -->
    <div id="child" onclick="console.log('child clicked')"> <!-- Child node --> 
        Child
    </div>
</div>
Now we have two different handlers. Clicking the child node would perform these handlers in different orders based on which mode we want the event to be executed in.
  • In bubbling mode, which is the default mode, the event will be triggered at the deepest element. Then it will be bubbled up to the its parents.
Clicking the child node will print child clicked, and then parent clicked.
  • In capturing mode, the order is opposite. The handler will be invoked from the parent element first, then down to the its children.
We can force the event to be fired in the capturing mode by passing the third parameter of addEventListener(event, handler, useCapture) to true.
Let's revisit the example by using addEventListener():
document.getElementById('parent').addEventListener('click', () => {
    console.log('parent clicked');
}, true);

document.getElementById('child').addEventListener('click', () => {
    console.log('child clicked');
});
If we click the child node, the listener of parent node is fired first, and then the child node's listener. The Console window will output as follow:
parent clicked
children clicked

Good practice

It is not recommended to registry the event handler via the element attributes such as onclick. For more details, check out the addEventListener() function vs onproperty.

Good to know

The capturing mode does not happen for some special events (focus, for example) and on IE < 9.

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