# Demonstrating the dangers of using prefixed and non prefixed event listeners.

Once the parent box slides in, an animationend event is fired which console.logs out 'Done'. The event is attached with jQuery's one method so the event should only fire once. If you click on the child box now, it will also animate but when it finishes, the parent div's animationend event fires again and consoles out 'Done'.

Two things to look out for here. The jQuery.one method will attach the events once and remove the event that is fired. So after the first animationend, it is removed but the webkitAnimationEnd remains. The second thing is that animationend events bubble just like click, mouseup etc so when the child box animationend fires the event is handled but propagation is not stopped and therefore it triggers the remaining webkitAnimationEnd event on the parent element.