jQuery vs DOM return false

What does return false do inside a JavaScript event handler? What does it do in a jQuery event handler? Are they the same thing?

The short answer is “no”. return false in a native JavaScript event handler prevents the default behaviour of the event. It’s the equivalent of event.preventDefault(). This is the same for DOM level 0 event handlers like this:

element.onclick = function () { };

and DOM level 2 event handlers like this:

element.addEventListener('click', function () {});

return false in jQuery, on the other hand, will stop the default behaviour and stop the event propagating. This can be seen in the jQuery source:

if ( ret === false ) {
  event.preventDefault();
  event.stopPropagation();
}

If the return value of the handler is false, jQuery will call preventDefault and stopPropagation on the event object.

I’ve made a fiddle to demonstrate this behaviour, showing what return false does with DOM level 0 and level 2 handlers, and with jQuery handlers.