Event Bubbling and Capturing

Understand event propagation phases

IntermediateTopic: Events Programs

JavaScript Event Bubbling and Capturing Program

This program helps you to learn the fundamental structure and syntax of JavaScript programming.

// Event Bubbling (default)
// Event flows from target to root

const parent = document.getElementById('parent');
const child = document.getElementById('child');

// Bubbling phase (default)
parent.addEventListener('click', function(e) {
    console.log('Parent clicked (bubbling)');
});

child.addEventListener('click', function(e) {
    console.log('Child clicked (bubbling)');
    // e.stopPropagation(); // Stop bubbling
});

// Clicking child will log:
// 1. Child clicked (bubbling)
// 2. Parent clicked (bubbling)

// Event Capturing (useCapture = true)
// Event flows from root to target

parent.addEventListener('click', function(e) {
    console.log('Parent clicked (capturing)');
}, true); // true = capturing phase

child.addEventListener('click', function(e) {
    console.log('Child clicked (capturing)');
}, true);

// Clicking child will log:
// 1. Parent clicked (capturing)
// 2. Child clicked (capturing)

// Method 3: Both phases
parent.addEventListener('click', function(e) {
    console.log('Parent - Capturing');
}, true);

parent.addEventListener('click', function(e) {
    console.log('Parent - Bubbling');
}, false);

child.addEventListener('click', function(e) {
    console.log('Child - Capturing');
}, true);

child.addEventListener('click', function(e) {
    console.log('Child - Bubbling');
}, false);

// Clicking child logs:
// 1. Parent - Capturing
// 2. Child - Capturing
// 3. Child - Bubbling
// 4. Parent - Bubbling

// Method 4: Stop propagation
child.addEventListener('click', function(e) {
    e.stopPropagation(); // Stop at this element
    console.log('Event stopped');
});

// Method 5: Stop immediate propagation
child.addEventListener('click', function(e) {
    e.stopImmediatePropagation(); // Stop all handlers
    console.log('All handlers stopped');
});

Output

// Output depends on which element is clicked

Understanding Event Bubbling and Capturing

Event propagation has two phases.

Bubbling Phase (default)

•Event flows from target to root

•Bottom-up propagation

•Most common use case

Capturing Phase

•Event flows from root to target

•Top-down propagation

•Use third parameter: true

Event Flow

1.Capturing: Root → Target

2.Target: At target element

3.Bubbling: Target → Root

stopPropagation()

•Stops event from propagating

•Prevents parent handlers

stopImmediatePropagation()

•Stops all handlers on element

•More aggressive than stopPropagation()

Use Cases

•Event delegation

•Performance optimization

•Complex interactions

Let us now understand every line and the components of the above program.

Note: To write and run JavaScript programs, you need to set up the local environment on your computer. Refer to the complete article Setting up JavaScript Development Environment. If you do not want to set up the local environment on your computer, you can also use online IDE to write and run your JavaScript programs.

Event Delegation

Custom Events