Understanding the Differences: event.stopPropagation(), event.preventDefault(), and return false

When it comes to handling DOM events in JavaScript, it’s common to get confused about when to use event.stopPropagation(), event.preventDefault(), or simply return false. In this blog, we’ll clarify the purpose of each and guide you on their appropriate usage.

event.stopPropagation()

The stopPropagation() method of an Event object allows you to prevent event bubbling. Event bubbling is the natural propagation of an event from a specific element to its parent elements. By default, an event fired on a DOM element will propagate to its parents unless stopped.

If you want to handle a click event on an element and ensure that it stops at your event handler, you can call stopPropagation() at the end of the event handler. This will prevent the event from reaching any additional parent elements.

const link = document.getElementById('my-link');
link.addEventListener('mousedown', event => {
  // process the event
  // ...
  event.stopPropagation();
});

event.preventDefault()

The preventDefault() method of the event object allows you to cancel the default behavior associated with the event. For example, clicking on an a element triggers the default behavior of opening a new page. Similarly, submitting a form triggers the default behavior of submitting the form.

Calling preventDefault() will cancel this default behavior and give you the opportunity to customize the action. For instance, you can use it to make a fetch request and load JSON instead of opening a new page on a link click.

Other event handlers defined on the same element will still execute unless event.stopImmediatePropagation() is called.

Returning false

Returning false is commonly seen in jQuery, where it automatically invokes event.preventDefault() and event.stopPropagation() for you. However, in vanilla JavaScript, returning false in an event handler does nothing. It’s important to note that return false alone will not cancel the default behavior or stop event propagation.

To achieve the same effect as event.preventDefault() and event.stopPropagation(), you must explicitly call these methods in your event handler.

Understanding the differences and appropriate usage of event.stopPropagation(), event.preventDefault(), and return false is crucial for handling DOM events effectively in JavaScript.