DOM events: stopPropagation vs preventDefault() vs. return false
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Which one to use between `event.stopPropagation()`, `event.preventDefault()` and `return false` in events
I feel like I’m always confused by one thing when it comes to handling DOM events in JavaScript.
When should I call stopPropagation()
on the event object?
When should I call preventDefault()
on the event object?
Should I return false
?
Event.stopPropagation
Suppose I want to handle a click event on an element.
By default an event on a DOM element is fired on the specific element clicked (say, a button) and will be propagated to all its parent elements tree, unless it’s stopped.
I want to make sure the event is handled in my event handler, and it will “stop” there.
You can stop the propagation by calling stopPropagation()
method of an Event
object, usually at the end of the event handler:
const link = document.getElementById('my-link')
link.addEventListener('mousedown', event => {
// process the event
// ...
event.stopPropagation()
})
Event.preventDefault
Calling the preventDefault()
method of the event object will cancel the default handling that the browser is programmed to execute.
Opening a new page on an a
element click
event, for example.
Or submitting a form
on the submit
event.
Calling preventDefault()
is what you need to do to completely customize the action. Perhaps by creating a fetch
request to load some JSON instead of opening a new page on a link click.
Other event handlers defined on this same element will execute. Unless you call event.stopImmediatePropagation()
.
Returning false
This is especially confusing to former (or current) jQuery developers. In jQuery, returning false
from an event handler automatically called Event.preventDefault
and Event.stopPropagation
for us.
In vanilla JavaScript, return false
in an event handler does nothing.
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